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GIOVANNI FRANCESCHINI

Professore Ordinario presso: Dipartimento di Ingegneria "Enzo Ferrari"


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Pubblicazioni

- A DC/DC three-phase converter [Brevetto]
Violi, F.; Franceschini, G.; Bellini, Alberto; Lorenzani, Emilio; Cavatorta, M.
abstract

A DC/DC three-phase converter is obtained replacing the one-phase transformer of a traditional switching amplifier with a three-phase transformer (1). The DC/DC three-phase converter allows obtaining a reduction of the harmonic distortion of the continuous output signal of the feeder and a lower power loss on the transformer with the same power.


- Amplificatore Audio di Potenza “TANDEM Elettrico” [Brevetto]
Franceschini, G.; Bellini, Alberto; DE BENEDETTI, A.; Burlenghi, M.; Ugolotti, E.
abstract

Gli amplificatori audio di potenza sono largamente impiegati in diversi settori dell’elettronica di consumo. Recentemente gli amplificatori di tipo switching si sono affermati grazie all’elevato rendimento e alla economicità costruttiva che ne deriva. Gli amplificatori di tipo switching (conosciuti anche come amplificatori che operano in classe D, quindi abbreviati come “Classe D” ) ricevono come ingresso un segnale modulato a larghezza di impulso (PWM). Per ottenere l’amplificazione tale ingresso viene utilizzato per parzializzare un livello di tensione elevato, pari alla tensione di alimentazione disponibile. Questo determina nella corrente di uscita una elevata ondulazione, che si traduce in una elevata distorsione armonica del suono prodotto dall’altoparlante.Inoltre la banda dell’amplificatore è legata alla frequenza della modulazione PWM, che, a causa della velocità di commutazione limitata degli interruttori statici non può essere elevata.Quindi per un amplificatore switching ad un elevato rendimento si contrappone una significativa distorsione, e la difficoltà di ottenere una banda passante elevata.D’altra parte gli amplificatori lineari comunemente utilizzati, (in bibliografia noti come amplificatori operanti in classe A, AB, B) hanno una distorsione relativamente bassa, ma la loro efficienza è nettamente inferiore a quella di un Classe D.


- Amplificatore Audio di Potenza “TANDEM Magnetico” [Brevetto]
Franceschini, G.; Bellini, Alberto; DE BENEDETTI, A.; Burlenghi, M.; Ugolotti, E.
abstract

Gli amplificatori audio di potenza sono largamente impiegati in diversi settori dell’elettronica di consumo. Recentemente gli amplificatori di tipo switching si sono affermati grazie all’elevato rendimento e alla economicità costruttiva che ne deriva. Gli amplificatori di tipo switching (conosciuti anche come amplificatori che operano in classe D, quindi abbreviati come “Classe D” ) ricevono come ingresso un segnale modulato a larghezza di impulso (PWM). Per ottenere l’amplificazione tale ingresso viene utilizzato per parzializzare un livello di tensione elevato, pari alla tensione di alimentazione disponibile. Questo determina nella corrente di uscita una elevata ondulazione, che si traduce in una elevata distorsione armonica del suono prodotto dall’altoparlante.Inoltre la banda dell’amplificatore è legata alla frequenza della modulazione PWM, che, a causa della velocità di commutazione limitata degli interruttori statici non può essere elevata.Quindi per un amplificatore switching ad un elevato rendimento si contrappone una significativa distorsione, e la difficoltà di ottenere una banda passante elevata.D’altra parte gli amplificatori lineari comunemente utilizzati, (in bibliografia noti come amplificatori operanti in classe A, AB, B) hanno una distorsione relativamente bassa, ma la loro efficienza è nettamente inferiore a quella di un Classe D.


- Audio Power Amplifier [Brevetto]
Franceschini, G.; Bellini, Alberto; DE BENEDETTI, A.; Burlenghi, M.; Ugolotti, E.
abstract

SUMMARY An audiopower amplifier achieved with a hybridarchitecture constituted by the magnetic couplingof a linear amplifier with a switching amplifierplaced on two coaxial coils of a loudspeaker, or with a hybrid architecture constituted by the electrical coupling of a linear amplifier with a switchingamplifier.These solutions allow obtainingan amplifier characterized by the low distortion of a linear amplifier and by the high efficiency of the switching amplifier.


- Convertitore DC/DC trifase [Brevetto]
Violi, F.; Franceschini, G.; Bellini, Alberto; Lorenzani, Emilio; Cavatorta, M.
abstract

Un convertitore DC/DC trifase è ottenuto sostituendo il trasformatore monofase di un tradizionale amplificatore tipo switching, con un trasformatore trifase (1). Grazie alle intrinseche caratteristiche del sistema trifase, si ottiene una riduzione della distorsione armonica del segnale continuo in uscita dall’alimentatore.


- Convertitore dc-ac, in particolare per fornire energia elettrica da un pannello solare ad una rete elettrica [Brevetto]
Barater, D.; Crinto, A. S.; Franceschini, G.; Lorenzani, Emilio; Riboli, G.
abstract

Convertitore DC-AC, in particolare per fornire energia elettrica da un pannello solare ad una rete elettrica comprendente: una sezione di ingresso (10) per ricevere una tensione sostanzialmente continua; un ponte H (20), adatto a ricevere detta tensione sostanzialmente continua tramite detta sezione di ingresso (10), e predisposto a fornire in uscita una tensione sostanzialmente alternata, detto ponte H (20) essendo pilotabile almeno nelle seguenti condizioni: almeno una condizione operativa, in cui viene fornita energia elettrica a detta rete elettrica (2); una prima e seconda condizione di ricircolo, in cui una corrente fluisce attraverso almeno una parte di detto ponte H (20), e non viene fornita energia elettrica a detta rete elettrica (2). Il convertitore (1) comprende inoltre: una sezione di uscita (40), per fornire detta tensione sostanzialmente alternata a detta rete elettrica (2); modulo di disaccoppiamento (50),operativamente interposto tra detta sezione di ingresso (10) e detto ponte H (20), e configurato per disaccoppiare detta sezione di ingresso (10) da detto ponte H (20) in corrispondenza di dette prima e seconda condizione di ricircolo di detto ponte H (20).


- DC-AC converter, in particular for providing power supply from a solar panel to a mains power supply [Brevetto]
Andrea Stefano Crinto, ; Franceschini, Giovanni; Lorenzani, Emilio; Giuseppe, Riboli
abstract

A DC-AC converter, in particular for providing electric energy from a solar panel to an electric network, comprising: an input section (10) for receiving a substantially direct voltage; an H-bridge (20) adapted to receive said substantially direct current through said input section (10) and designed to output a substantially alternating voltage, said H-bridge (20) being drivable at least in the following conditions: at least one operating condition, at which electric energy is supplied to said electric network (2); a first and a second recirculation condition, at which a current flows through at least part of said H-bridge (20), and no electric energy is supplied to said electric network (2). The converter (1) further comprises: an output section (40) to supply said substantially alternating current to said electric network (2); an uncoupling module (50) operatively interposed between said input section (10) and said H-bridge (20) and configured for uncoupling said input section (10) from said H-bridge (20) at said first and second recirculation conditions of said H-bridge (20).


- Metodo e Dispositivo per controllare la tensionegenerata da un generatore elettrico asincrono [Brevetto]
Borghi, G.; Franceschini, G.; Lorenzani, Emilio
abstract

La soluzione proposta prevede di controllare la corrente di magnetizzazione del generatore e quindi la tensione erogata tramite un convertitore elettronico (inverter trifase). Questo è un dispositivo con un elevato rendimento e con una dinamica di intervento pressoché istantanea se riferita alla frequenza industriale.Il convertitore sarà inserito nel sistema di cogenerazione secondo la figura 3. Lo schema di controllo misurerà e ricostruirà il vettore rappresentativo del flusso al traferro del generatore e lo userà come riferimento di fase. A questo punto due anelli di controllo delle correnti saranno in grado di erogare od assorbire con continuità (entro i limiti fisici dell’inverter) correnti rispettivamente in fase o in quadratura con il flusso. Compito del controllo sarà mantenere la tensione del generatore al valore nominale manipolando opportunamente la corrente di magnetizzazione che risulta essere la corrente in fase col flusso. La figura 4 mostra su di un diagramma vettoriale il meccanismo con cui risulta possibile mantenere la tensione generata al valore voluto compensando l’effetto dei carichi sul flusso del generatore.


2021 - Considerations on the preliminary sizing of electrical machines with hairpin windings [Relazione in Atti di Convegno]
Soltani, M.; Nuzzo, S.; Barater, D.; Franceschini, G.
abstract

Although the standard preliminary sizing of electrical machines equipping random windings is well consolidated and is worldwide acknowledged to be a good starting point for the design, there is no proof of accuracy and confidence when it comes to hairpin windings. This winding technology is gaining extensive attention due to its inherently high slot fill factor, good heat dissipation, strong rigidity, and short end-windings. These features make hairpin windings a potential candidate for some traction application to enhance power and/or torque densities. In this paper, a comparative design is done using the classical sizing tools available in literature between two surface-mounted permanent magnet synchronous machines, one featuring a random winding and one with a hairpin layout. The study aims at highlighting the hairpin winding challenges at high frequency operations and at showing limits of applicability of these standard approaches when applied to this technology. For verification purposes, finite element evaluations are also performed.


2021 - Design and thermal assessment of a high performance electric motor for racing applications [Relazione in Atti di Convegno]
Rossi, N.; Matteazzi, N.; Petti, G. L.; Fazzini, L.; Nuzzo, S.; Barater, D.; Franceschini, G.
abstract

Recently, an increasing attention in electric and hybrid vehicles is taking place. In order to raise awareness and technical knowledge on vehicles with reduced carbon footprint, several electric car competitions have been launched. Formula SAE is one of these, where talented students from different universities around the globe compete to design a fully electric racing car. This requires the development of high power density drives, with accurate electromagnetic and thermal analyses.This paper presents the design process and the thermal assessment of a high-performance electric motor intended for a FSAE racing car. The starting requirements for the electromagnetic and thermal designs are based on realistic available data from previous competitions and championship regulations.


2021 - Design of the propulsion system for a formula sae racing car based on a brushless motor [Relazione in Atti di Convegno]
Devito, G.; Nuzzo, S.; Barater, D.; Franceschini, G.; Papini, L.; Bolognesi, P.
abstract

Today, an ever-increasing interest in electric propulsion is occurring due to the need of decarbonizing the society in order to avoid a catastrophic climate collapse. To raise awareness on this challenge, Formula SAE, an international university competition in engineering design, has also established an electric propulsion championship. This paper proposes a low budget motor propulsion system for Formula SAE racing cars. The design is based on realistic data available from previous race editions and suitably analyzed for the application at hand. Besides the budget limitation, which constitutes the main design guideline in this work, a set of constraints imposed by the race regulations are considered. Consequently, the performance requirements are defined, and the ensuing propulsion motor design is carried out through a preliminary analytical sizing followed by a finite-element validation and refinement. A good trade-off between cost and performance is achieved in terms of motor design and overall propulsion system architecture.


2021 - Improvement on Flux Weakening Control Strategy for Electric Vehicle Applications [Articolo su rivista]
Bianchini, Claudio; Franceschini, Giovanni; Torreggiani, Ambra
abstract

This paper proposes an optimized flux weakening (FW) control strategy for interior permanent-magnet synchronous electric motor to address the critical issues that could occur under torque setpoint transition in flux weakening region, due, for example, to an emergency braking. This situation is typical in electric vehicles where the electrical machines operate over a wide speed range to reach high power density and avoid gearboxes. Two modified traditional flux weakening strategies are proposed in this paper to improve torque control quality during high speed torque transition. The proposed modified control strategies were validated both by Matlab/Simulink simulations, modeling the power train of a light vehicle application, and extensive experimental tests on a dedicated test bench.


2021 - Multi three-phase hairpin windings for high-speed electrical machine: Possible implementations [Relazione in Atti di Convegno]
Pastura, M.; Barater, D.; Nuzzo, S.; Franceschini, G.
abstract

This work provides an in-depth critical analysis related to the feasibility of combining multi three-phase winding layouts with the ever-spreading hairpin technology. After an introduction on the advantages and challenges of both hairpin and multi-phase windings, more details on how these two technologies can be combined are provided. Then two similar stator geometries, with 72 and 96 slots, are analyzed in detail exploiting an 8 poles permanent magnet - assisted synchronous reluctance motor for traction applications. A relevant set of feasible winding configurations are modelled and analyzed through finite element simulations. For every machine, a breakdown of the power losses is provided and compared against that of the same machine topologies having random-wound windings with stranded round conductors. The main results and possible solutions to increase the machine performance are then provided.


2021 - Partial Discharges in Electrical Machines for the More Electric Aircraft. Part I: A Comprehensive Modelling Tool for the Characterization of Electric Drives based on fast switching semiconductors [Articolo su rivista]
Pastura, M.; Nuzzo, S.; Immovilli, F.; Toscani, A.; Rumi, A.; Cavallini, A.; Franceschini, G.; Barater, D.
abstract

The arrival on the market of new power devices based on wide bandgap semiconductors has raised a relevant interest due to their superior properties compared to conventional technologies. On the other hand, these devices are inherently characterized by high rates of voltage changes over time, which may result in reliability challenges in electric drives adopting them. In fact, dangerous voltage overshoots at the motor terminals and uneven voltage distributions within the machine windings may occur. These phenomena can trigger a high insulation stress and partial discharges and, as a consequence, they may concur to the premature failure of the dielectric materials. This paper proposes a flexible and comprehensive modelling approach for the accurate analysis and estimation of both voltage overshoots and voltage distributions in a typical converter-cable-motor system intended for more electric aircraft applications. The modelling results are validated against experimental measurements carried out on a physical prototype comprising a wide bandgap-based converter, a connecting cable and an electrical machine stator. The findings are then used in the companion papers (part II and part III) to investigate the dependence of partial discharge phenomena on these voltage waveforms, highlight reliability challenges in modern ±270 V DC bus voltage drives for the more electric aircraft and discuss solutions.


2020 - An analytical approach for the design of innovative hairpin winding layouts [Abstract in Atti di Convegno]
Arzillo, A.; Nuzzo, S.; Braglia, P.; Franceschini, G.; Barater, D.; Gerada, D.; Gerada, C.
abstract

This work deals with an analytical approach aimed at accurately predicting Joule losses in innovative hairpin winding layouts. While hairpin windings are seeing an everincreasing use in automotive and aerospace applications due to their inherently high slot fill factor, they also present drawbacks such as the non-uniform current distribution potentially occurring across their cross section. This phenomenon is emphasized at high frequencies, leading to a significant increase of the effective conductor resistance and, consequently, of copper losses. Hence, particular attention has to be given to the design of electrical machines employing hairpin conductors, aiming to reduce the high-frequency losses as much as possible. In this paper, an analytical model based on previous investigations is updated and modified in order to increase the degrees of freedom in the design and analysis of hairpin windings. With the developed analytical model, the copper losses associated to innovative hairpin configurations can be accurately predicted. The findings also confirm that such alternative layouts can effectively reduce the Joule losses when compared to traditional hairpin technologies.


2020 - Challenges and Future opportunities of Hairpin Technologies [Relazione in Atti di Convegno]
Arzillo, A.; Braglia, P.; Nuzzo, S.; Barater, D.; Franceschini, G.; Gerada, D.; Gerada, C.
abstract

Hairpin windings are seeing an ever-increasing application and development in electrical machines designed for high power and torque densities. In fact, due to their inherently high fill factor, they are very attractive in applications, such as transportation, where these characteristics are considered main design objectives. On the other hand, high operating frequencies also contribute to improve power density of electrical machines. However, at high fundamental frequencies, hairpin windings are characterised by increased Joule losses due to skin and proximity effects. Hence, while these technologies are introducing new opportunities, a number of challenges still need to be addressed. These include manufacturing aspects, contacting processes, thermal management, etc. This paper presents an overview of the current state-of-the-art of hairpin technologies and propose possible future opportunities. The authors' perspective is then finally provided, showing how innovative winding patterns can potentially overcome the above mentioned challenges.


2020 - Minimization of network induced jitter impact on FPGA-based control systems for power electronics through forward error correction [Articolo su rivista]
Bianchi, V.; Savi, F.; De Munari, I.; Barater, D.; Buticchi, G.; Franceschini, G.
abstract

In modular distributed architectures, the adoption of a communication method that is at the same time robust and has a low and predictable latency is of utmost importance in order to support the required system dynamics. The aim of this paper is to evaluate the consequences of the random jitter on machine drives distributed control, caused by the messages’ re-transmission in case of an error in the received data. To achieve this goal, two different Forward Error Correction (FEC) techniques are introduced in the chosen protocol, so that the recipient of the message can correct random errors without the need of any additional round trip delays needed to request and obtain a re-transmission. Experimentally validated simulations are used to evaluate the impact of random network derived jitter on a real world closed loop control system for distributed power electronic converters.


2020 - Sensitivity analysis on the voltage distribution within windings of electrical machines fed by wide band gap converters [Abstract in Atti di Convegno]
Pastura, M.; Nuzzo, S.; Franceschini, G.; Sala, G.; Barater, D.
abstract

In the last years, Wide Band Gap devices are seeing a significant widespread in electric drives, due to their higher performance compared to conventional semiconductors. However, they also produce higher electric stress due to over-voltages and uneven voltage distributions among winding turns of electrical machines fed by them, which can lead to premature failures and/or reduced lifetimes.This paper presents a sensitivity analysis on the voltage distribution across stator winding turns of an electric motor intended for aerospace applications. The effects of the surge voltage characteristic parameters, such as dv/dt, voltage magnitude and parasitic impedances, are investigated. An equivalent circuit approach, based on the multi-transmission line theory, is developed and implemented in MatLab-Simulink environment, while the relevant circuital parameters are estimated through finite element analysis performed with MagNet and ElecNet software.


2020 - Slot design optimization for copper losses reduction in electric machines for high speed applications [Articolo su rivista]
Bianchini, C.; Vogni, M.; Torreggiani, A.; Nuzzo, S.; Barater, D.; Franceschini, G.
abstract

The need of a wide operating range and a high power density in electric machines for fulland hybrid electric vehicles in traction applications has led to an increase in the operating frequency of the machine. When the electric frequency increases, the additional losses in stator windings become an issue and they have to be taken into account in the design of the electric machine. This issue is more critical when hairpin windings are employed, due to the the skin and proximity effects which produce increased copper losses. In this paper, the relationships between different stator slot parameters (tooth width, slot opening, etc.) and stator winding copper losses have been analysed in order to identify an optimal design of a single stator slot.


2019 - Assessment of efficiency and reliability of wide band-gap based H8 inverter in electric vehicle applications [Articolo su rivista]
Concari, L.; Barater, D.; Toscani, A.; Concari, C.; Franceschini, G.; Buticchi, G.; Liserre, M.; Zhang, H.
abstract

This paper analyzes the performance of a three-phase converter architecture with a reduced common mode voltage to be used in electric motor drives. Starting from the classical three-phase bridge architecture, two additional switches are inserted in the DC link, in order to decouple the source from the load during the freewheeling intervals. Ad-hoc modulation strategies are introduced and evaluated against the classical three-phase space vector modulation. Three main parameters are analyzed: common mode voltage, efficiency and reliability. Experimental measurements on a converter prototype are used to evaluate the common mode performance. The efficiency in the case of Si-IGBT and SiC-MOSFETs is experimentally evaluated. Reliability analysis performed with a Coffin-Mason model showed that the higher efficiency offered by the SiC devices allows for a marked extension of the lifetime.


2019 - Design and Control of High-Density High-Voltage Smart Converter for Food Ohmic Heating [Articolo su rivista]
Soldati, A.; Toscani, A.; Cova, P.; Franceschini, G.
abstract

The design of an innovative converter for ohmic heating of fluid foods is presented. Application-specific requirements are addressed with new solutions and verified on a commercial-size 60-kW prototype. A multioutput high-voltage (0.8 to 4 kV) transformer with automatic tap change enriches a basic H-bridge topology, enabling processing of a wide set of foods and allowing grounding one of the outputs. High power density is achieved by power switches Pareto optimization in the reliability-efficiency objectives and by pushing the switching frequency up to 30 kHz, solving the electrode corrosion problem, too. Reproducible and reliable operation is assured by three different control strategies: load variability is dealt with high-dynamics power control, repeatable output is guaranteed by input voltage compensation, and optimal working point is ensured by control of the transformer primary current dc component. This last control also allows removing the output capacitors, improving density metrics with respect to the state-of-the-art. Analytical models for all control strategies are given to support dynamic performance tuning while guaranteeing stability.


2019 - Enhanced Internal Permanent-Magnet Machines Flux Weakening Control Strategies for Traction Applications [Relazione in Atti di Convegno]
Fornari, Raffaele; Franceschini, Giovanni; David, Danilo; Torreggiani, Ambra; Bianchini, Claudio; Frigieri, Matteo
abstract


2019 - PWM impacts on the Reliability of DC/DC Converters with High-Frequency Transformer [Relazione in Atti di Convegno]
Barater, D.; Franceschini, G.; Lusuardi, L.; Cavallini, A.; Buticchi, G.
abstract

In the framework of the More Electric Aircraft, high efficiency and high reliability are the main concerns. Different standard exists regarding voltage and frequency of the electrical power distribution system, but DC systems are attracting an increased interest. In this context, the voltage conversion is normally implemented by means of a high-frequency isolated DC/DC power converters. However, the high-frequency waveforms generated by the power electronics may trigger partial discharge phenomena in the windings of the transformer, decreasing the reliability. This paper attempts to model the lifetime of a Dual Active Bridge (DAB) converter for aerospace applications.


2019 - Potential of Electrification Applied to Non-Road Diesel Engines [Relazione in Atti di Convegno]
Mattarelli, E.; Rinaldini, C. A.; Scrignoli, F.; Fregni, P.; Gaioli, S.; Franceschini, G.; Barater, D.
abstract

The new Stage 5 European regulation for Non Road Mobile Machinery has lowered the limits on pollutant emissions for all the categories of internal combustion engines. An interesting alternative to the implementation of sophisticated after-treatment systems is to downsize the engine, and provide the extra power for peak demands with an electric motor, installed in place of the flywheel. The paper explores the potential of this concept, applied to an industrial engine, manufactured by Kohler, and delivering a maximum power of 56 kW@2600 rpm. The study is supported by a comprehensive experimental characterization of the internal combustion engine and of the electric components. A representative duty cycle is also defined, on the basis of a set of measures, taken in real operating conditions. The analysis of this reference cycle is performed by using a GT-Suite model, comparing different power split strategies. It is found that the ICE total displacement can be reduced from 2.5 to 1.9 L (from 4 to 3 cylinders), without any penalization on powertrain performance and weight. A relevant reduction of soot (22%) and NOx (16%) emissions is observed, along with a slight reduction of fuel consumption.


2018 - Comprehensive Control System for Parallelable 60 Hz-2MVA Harbor AC/AC Converters [Articolo su rivista]
Cova, P.; Toscani, A.; Concari, C.; Franceschini, G.; Portesine, M.
abstract

A high-performance parallelable 2 MVA, 50/60 Hz ac/ac frequency converter for harbor applications was designed and built. A specific comprehensive digital control system was set up, in order to obtain optimal current sharing among two or more parallel power converters. The control, based on a master-slave strategy, also guarantees good system availability in case of faults, even when the master is affected, by switching off the faulty converter and assuring continuous system operation under power derating. The control system was designed using MATLAB/ Simulink/PLECS tools, and tested with reduced-scale prototypes. After fine tuning a good agreement between prototype measurements and simulations was obtained. The full-size system, composed of two 2 MVA converters, was then fabricated and tested, demonstrating performances compliant with the requirements and aligned with simulations and measurements performed on the prototypes.


2018 - Induction Machines with Rotor Faults: Analysis of the Physical Quantities for Different Operating Conditions and Machine Sizes for Improved Diagnostics [Relazione in Atti di Convegno]
Concari, C.; Pietrini, G.; Soldati, A.; Tassoni, C.; Toscani, A.; Franceschini, G.
abstract

This paper extends the authors' deep investigation of the electric rotor fault signatures of induction machines to machines of different size operating in various conditions. Authors researches have already shown the limits of the usual diagnostic procedures based on the sum of both left and right current sidebands. A proper faulty machine model leading to a more robust diagnosis has been proposed and the effect of machine size and load conditions on current space vector sidebands, flux, torque and speed spectral components is shown. These physical quantities, in case of small faults, can be described by their representative phasors in a synchronous reference frame. The analytical links among the phasors are validated by simulations and experiments. The prominent role of mechanical inertia in the diagnostic process is highlighted, assessing the range of validity of the usual diagnostic index versus machine size and load, eventually an alternative procedure is here proposed.


2017 - Investigation on H-8 VSI architecture for bearing currents mitigation in VFD [Relazione in Atti di Convegno]
Barater, D.; Franceschini, G.; Immovilli, F.; Lorenzani, E.
abstract

With the widespread adoption in the industry of variable frequency drives (VFD) for both small and large motor-inverter systems, rolling bearing showed a reduction of lifespan due to inverter-induced bearing currents [1]. Damages include generalized roughness due to pitting and fluting of the bearing races surfaces and rolling elements. These damages are directly related to current flowing between the bearing components and results in vibration, increased friction with associated heat generation and ultimately can lead to bearing seizure or catastrophic failure.


2017 - Multi-stress lifetime model of the winding insulation of electrical machines [Relazione in Atti di Convegno]
Pietrini, G.; Barater, D.; Immovilli, Fabio; Cavallini, A.; Franceschini, G.
abstract

In this paper, a novel multi-stress model which estimates the lifetime of the winding insulation relative to its duty cycle is proposed and investigated. With an adequate implementation of this model, then an electrical machine can be designed not only in terms of its performance requirements, but also considering the associated reliability and lifetime aspects. The determination of the model parameters is based on the results of accelerated thermo-mechanical ageing tests.


2017 - Multistress Characterization of Fault Mechanisms in Aerospace Electric Actuators [Articolo su rivista]
Barater, Davide; Immovilli, Fabio; Soldati, Alessandro; Buticchi, Giampaolo; Franceschini, Giovanni; Gerada, Christopher; Galea, Michael
abstract

The concept behind the more electric aircraft is the progressive electrification of on-board actuators and services. It is a way to reduce or eliminate the dependence on hydraulic, mechanical, and bleed air/pneumatic systems, and pursue efficiency, reliability, and maintainability. This paper presents a specialized test rig whose main objective is to assess insulation lifespan modeling under various stress conditions, especially investigating the interaction between ageing factors. The test setup is able to reproduce a multitude of environmental and operational conditions at which electric drives and motors, used in aerospace applications, are subjected. It is thus possible to tailor the test cycle in order to mimic the working cycle of an electrical motor during real operation in aircraft application. The developed test-rig is aimed at projecting the technology readiness to higher levels of maturity in the context of electrical motors and drives for aerospace applications. Its other objective is to validate and support the development of a comprehensive insulation degradation model.


2017 - OHMIC HEATER [Brevetto]
Roberto, Castelli; Stefano, Romei; Cova, Paolo; Toscani, Andrea; Soldati, Alessandro; Franceschini, Giovanni
abstract


2017 - Riscaldatore ohmico [Brevetto]
Catelli, Roberto; Cova, Paolo; Romei, Stefano; Soldati, Alessandro; Franceschini, Giovanni; Toscani, Andrea
abstract


2017 - Riscaldatore ohmico e metodo di funzionamento [Brevetto]
Catelli, Roberto; Franceschini, Giovanni; Cova, Paolo; Romei, Stefano; Soldati, Alessandro; Toscani, Andrea
abstract

Riscaldatore ohmico per il riscaldamento di un prodotto alimentare comprendente: - un inverter (3) comprendente interruttori (30) controllati; - una coppia (4) di elettrodi posizionabili a contatto con il prodotto alimentare da riscaldare, detto inverter (3) essendo operativamente interposto tra un raddrizzatore (2) della tensione di alimentazione e la coppia (4) di elettrodi; - un trasformatore (6) posto tra l'inverter (3) e la coppia (4) di elettrodi per regolare l'ampiezza della tensione; - mezzi (7) di determinazione della componente continua della corrente in una zona a valle dell'inverter (3) e a monte o in corrispondenza del trasformatore (6); - un sistema (800) di regolazione della durata di chiusura degli interruttori (30) di detto inverter (3) che opera in funzione dei mezzi (7) di determinazione della componente continua minimizzando/annullando detta componente continua.


2016 - An open problem for More Electrical Aircraft (MEA): How insulation systems of actuators can be qualified? [Relazione in Atti di Convegno]
Pietrini, Giorgio; Barater, Davide; Franceschini, Giovanni; Mancinelli, Paolo; Cavallini, Andrea
abstract

The concept of More Electric Aircraft (MEA) aims to address the demand for efficiency, reliability and maintainability of today aerospace industry by means of an in-depth electrification of the currently hydraulic, mechanical and pneumatic on-board actuators. The high power density of electric actuators shall decrease substantially the aircraft weight as well as its fuel consumption and environmental impact. However, safety and reliability are primary drivers of this sector. This paper will review the main stress factors affecting the lifespan of insulation materials used in aerospace actuators, concentrating in particular to the influence of the low atmospheric pressure at high attitude and to the effect of wide band-gap power devices' short rise times on voltage stress in windings.


2016 - Recent advances in single-phase transformerless photovoltaic inverters [Articolo su rivista]
Barater, Davide; Lorenzani, Emilio; Concari, Carlo; Franceschini, Giovanni; Buticchi, Giampaolo
abstract

Photovoltaic (PV) power systems have been in the spotlight of scientific research for years. However, this technology is still undergoing developments, and several new architectures are proposed each year. This study describes the main challenges facing grid-connected PV systems without galvanic isolation, then carries out a review of the state-of-the-art of single-phase systems. The converter topology review is focused on the match between the different types of converters and the different PV panel technologies, determined by the common-mode voltage between the PV string terminals and the ground. The ground leakage current, due to time variations of this voltage, is a source of electric safety and electromagnetic interference (EMI)-related problems, and its amplitude is constrained by international standards. The basic principles of operation of the different solutions are described, along with their strengths and drawbacks. Conversion efficiency is evaluated qualitatively comparing the semiconductor power losses. Finally, the future trends regarding semiconductor devices, PV panels and international regulations for single-phase grid-connected equipment are discussed, and indications on how these might steer future research efforts in PV converters are inferred.


2016 - Single-phase series active power filter with transformer-coupled matrix converter [Articolo su rivista]
Buticchi, Giampaolo; Barater, Davide; Concari, Carlo; Franceschini, Giovanni
abstract

This study presents a series active power filter based on a single-phase matrix converter. Back-to-back voltagesource converters with nested control loops and passive filters are normally used for this application. A matrix converter, as proposed in this study, allows a simpler implementation both in terms of hardware (no grid filter and no DC link) and of control. Moreover, a novel zero-voltage compensation technique is introduced in order to reduce the distortion around the input voltage zero crossing. Simulations and experiments are used to validate the considered control methods, confirming the feasibility of the proposed architecture.


2016 - Test Setup for multistress characterization of insulation degradation mechanisms in electric drives [Relazione in Atti di Convegno]
Barater, Davide; Soldati, Alessandro; Pietrini, Giorgio; Franceschini, Giovanni; Immovilli, Fabio; Galea, Michael; Gerada, Chris
abstract

In this paper a special test setup able to assess lifespan models of electrical motor insulation system under various stress conditions is proposed. The test bed will allow characterizing insulation degradation mechanisms under variable ambient and power supply parameters, from simple models, such as twisted pairs, up to coil form and complete machine operated at rated load.


2015 - A high-speed electric drive for the more electric engine [Relazione in Atti di Convegno]
Lusignani, Davide; Barater, Davide; Franceschini, Giovanni; Buticchi, Giampaolo; Galea, Michael; Gerada, Chris
abstract

This paper presents a high-speed drive to be used for electrically-assisted turbo charging in an internal combustion engine. The electrification of the turbo-charger system can enhance the performance and reduce the dynamic drawbacks that affect conventional solutions i.e. turbo-lag. However, the design of the electric drive presents some challenges, especially related to the thermally aggressive environment and the high rotational speed. Therefore, a system level design approach needs to be adopted, where all the different sub-systems of the drive are addressed simultaneously. Thus, this paper includes considerations for the thermal and electromagnetic machine design. Furthermore, a voltage source inverter featuring wide-bandgap SiC power devices is described, and a sensorless rotor position detection and digital control is used to drive the machine. Finally, the test setup and preliminary experimental results are presented.


2015 - Comparing control topologies for wide-bandgap power-device drivers: A simulation study [Relazione in Atti di Convegno]
Soldati, Alessandro; Barater, Davide; Concari, Carlo; Franceschini, Giovanni
abstract

Wide-bandgap power switches, based on SiC and GaN, are emerging on the semiconductor market. Standard resistor drivers are insufficient to exploit all the advantages of these new devices. Fine control over current and voltage waveforms during switching, equivalent on-state resistance and immunity to noisy environments, demand the development of dedicated drivers. This study aims at determining a suitable control topology for the gate (or base) terminal of the power device, in order to enact regulation of the switching waveforms and performances. Four different topologies, both open- and closed-loop are simulated, examined, and compared with the standard resistor driver.


2015 - Multistress characterization of insulation aging mechanisms in aerospace electric actuators [Relazione in Atti di Convegno]
Barater, D.; Buticchi, G.; Soldati, A.; Franceschini, G.; Immovilli, Fabio; Galea, Michael; Gerada, Chris
abstract

The concept behind the More Electric Aircraft (MEA) is the progressive electrification of on-board actuators and services. It is a way to reduce or eliminate the dependence on hydraulic, mechanical and the bleed air/pneumatic systems and pursue efficiency, reliability and maintainability. This paper presents a review of the main stress factors affecting the lifespan of insulation materials in aerospace applications. A special test bed is also proposed, to assess insulation lifespan modelling under various stress conditions, especially investigating the interaction between ageing factors. The test bed will allow to characterize insulation degradation under variable ambient and power supply parameters for simple models such as twisted pairs, up to coil form and complete machine operated at rated load. The proposed approach is based on the design of experiments (DOE). The results of the work that will be carried out will allow to identify the most influential factors affecting insulation lifetime and the interactions between them.


2014 - A Nine-Level Grid-Connected Converter Topology for Single-Phase Transformerless PV Systems [Articolo su rivista]
Buticchi, G.; Barater, D.; Lorenzani, Emilio; Concari, C.; Franceschini, G.
abstract

This paper presents a single-phase transformerless grid-connected photovoltaic converter based on two cascaded full bridges with different dc-link voltages. The converter can synthesize up to nine voltage levels with a single dc bus, since one of the full bridges is supplied by a flying capacitor. The multilevel output reduces harmonic distortion and electromagnetic interference. A suitable switching strategy is employed to regulate the flying-capacitor voltage, improve the efficiency (most devices switch at the grid frequency), and minimize the common-mode leakage current with the help of a novel dedicated circuit (transient circuit). Simulations and experiments confirm the feasibility and good performance of the proposed converter.


2014 - Fault tolerant PWM generation with doubleredundant logic [Relazione in Atti di Convegno]
Troni, F.; Concari, C.; Toscani, A.; Buticchi, G.; Franceschini, G.
abstract

To improve reliability some systems adopt double redundancy; however, some failure conditions may prevent the normal operation of the machine or the machine to reach a safe state. The method proposed in this paper allows the normal operation of the system even in a fault condition of the control unit. The signals resulting from the parallel execution of code are modulated to a higher frequency and decoupled from each control stage using two capacitors; the information is then demodulated to obtain the control signal, either in the case of one or two branches working in the control unit. © 2014 WIT Press.


2014 - Frequency-based control of a micro-grid with multiple renewable energy sources [Relazione in Atti di Convegno]
Buticchi, Giampaolo; Liserre, Marco; Barater, Davide; Concari, Carlo; Soldati, Alessandro; Franceschini, Giovanni
abstract

Stand-alone micro-grids need a proper management of the active power exchange. This work is focused on the parallel operation of multiple grid-connected converters in an island-grid system. The proposed solution features a master inverter which emulates the grid and multiple grid-connected converters operating in parallel. The current sharing and overload protection is achieved by small frequency variations of master inverter's output, that are detected by the grid-connected converters. This mechanism exploits the behavior of the derating characteristics embedded in grid-connected inverters, that must reduce the output power if the grid frequency increases. In this case, standard grid-connected equipment can be used to realize micro-grids without the need of digital communication between the power units. Two possible scenarios are analyzed: low-power microgrid with master/slave converters, and low voltage grid fed by a Smart Transformer (ST) which performs the frequency control.


2014 - Performance analysis of SiC MOSFET based 3-level ANPC grid-connected inverter with novel modulation scheme [Relazione in Atti di Convegno]
Gurpinar, Emre; De, Dipankar; Castellazzi, Alberto; Barater, Davide; Buticchi, Giampaolo; Franceschini, Giovanni
abstract

Performance analysis of three-level active neutral point clamped (ANPC) inverter with 650V SiC MOSFETs by ROHM is presented with a new switching pattern that utilises the active rectification capability of SiC devices. Performance analysis of the converter with 700V DC link and 230Vrms grid voltage are presented for different switching frequency, device case temperature and load conditions. The switching frequency is varied from 10kHz to 80kHz at four different output power and four different heat sink temperature conditions. The experimental results show that the converter can maintain high efficiency under wide load, frequency and heat sink temperature conditions. Robust performance of SiC devices can lead to reduction in passive component size, by utilizing high switching frequency and heat sink weight and volume by operating SiC at higher case temperature conditions. © 2014 IEEE.


2014 - Performance analysis of UniTL-H6 inverter with SiC MOSFETs [Relazione in Atti di Convegno]
Barater, Davide; Buticchi, Giampaolo; Concari, Carlo; Franceschini, Giovanni; Gurpinar, Emre; De, Dipankar; Castellazzi, Alberto
abstract

A transformerless single-phase PV inverter has been tested with latest generation 650V/ 20A SiC MOSFETs from ROHM. Test results show that the inverter can be operated with high efficiency at high switching frequencies due to high switching and conduction performance of the devices. Results also show that reduction in output filter size, reduced harmonic distortion and increase in power density are enabled by SiC MOSFETs for PV inverters without compromising on the efficiency of the system. © 2014 IEEE.


2013 - A Five-Level Single-Phase Grid-Connected Converter for Renewable Distributed Systems [Articolo su rivista]
Buticchi, G.; Lorenzani, Emilio; Franceschini, G.
abstract

In low-power renewable systems a single-phase grid-connected converter is usually adopted. This paper deals with a novel five-level converter topology that follows this trend. A review of the state of the art of the five-level topologies and a theoretical power loss comparison with the proposed solution is realized. The proposed converter architecture is based on a full-bridge topology with two additional power switches and two diodes connected to the midpoint of the DC Link. Since the two added levels are obtained by the discharge of the two capacitors of the DC Link, the balancing of the midpoint voltage is obtained with a specific PWM strategy. Simulation and experimental results show the effectiveness of the proposed solution.


2013 - Improved control strategy for modular 2MVA AC/AC power converter [Relazione in Atti di Convegno]
Concari, Carlo; Cova, Paolo; Franceschini, Giovanni; Toscani, Andrea; Bertoluzza, Fulvio
abstract

A 2 MVA 50→60 Hz high performance parallelable frequency converter for harbor application was designed, fabricated, and tested. To increase output power, a smart digital control scheme was implemented; it can parallel two or more power converters with optimum current sharing among them and a good robustness to malfunctioning. Moreover the control can identify a faulty converter and, switching it off, it assures system continuous operations in derating conditions. This attractive feature is worth from availability point of view since it allows restoring full operating conditions without plant shutdown. The control strategy was developed and simulated in MATLAB Simulink/PLECS environment and then tested on a scaled prototype. Once a satisfactory agreement between simulation and prototype was obtained a full size system composed by two 2 MVA converters was built. Measurements performed on full size system confirmed the achievement of the specifications. © 2013 IEEE.


2013 - Single-phase matrix converter for active power filter applications [Relazione in Atti di Convegno]
Barater, Davide; Buticchi, Giampaolo; Concari, Carlo; Concari, Luca; Franceschini, Giovanni
abstract

This paper presents an AC/AC active power filter based on a single-phase matrix converter (SPMC). The use of a matrix topology allows to eliminate the reactive components normally used for temporary energy storage, reducing the size of the power converter and improving its reliability. The filter operates in series with the load through a step-down transformer, also allowing for a limited regulation of the fundamental voltage (boost/reduction). Several control methods are evaluated; in particular, a novel zero voltage compensation technique is introduced in order to reduce distortion around the input voltage zero crossing. Simulations and experiments are used to validate the considered control methods, and confirm the feasibility of the proposed solution. © 2013 IEEE.


2013 - Validation of a faulted rotor induction machine model with an insightful geometrical interpretation of physical quantities [Articolo su rivista]
Concari, Carlo; Franceschini, Giovanni; Tassoni, Carla; Toscani, Andrea
abstract

Many proposals about induction-machine broken-bar detection can be found in the literature. Disturbances that affect phase currents, current space vector, power, fluxes, torque, and speed have been utilized to diagnose mains-supplied machines. Nevertheless, there is still disagreement about how the fault signatures of the different variables correlate with the actual fault and how they depend on the operating conditions. This paper presents a simple but effective analytical representation of induction machines with rotor faults, based on a synchronous reference frame and on Steinmetz's phasors. The developed relationships can be visualized through equivalent circuits, feedback loop block diagrams, or geometrical loci, allowing a deep understanding of the underlying physical phenomena, particularly as functions of inertia and of the machine parameters. The insight thus gained helps to enhance the quantification of fault severity with respect to the usual diagnostic technique based on the sum of the sidebands, clearly defining for the first time the field of validity of such technique. The analytical results are verified through simulations and experiments. © 1982-2012 IEEE.


2013 - Vibrationless alignment algorithm for incremental encoder based BLDC drives [Articolo su rivista]
Concari, C.; Franceschini, G.; Toscani, A.
abstract

Incremental encoder based BLDC drives are widely employed in industry whenever smooth and efficient operation is needed in the whole speed range. Their weak spot lies in the need for a phase of initial alignment, traditionally performed by forcing the motor through a series of fixed phase supply configurations in an open loop stepping mode. This strategy of alignment causes ample mechanical vibrations which can be intolerable for certain applications. This paper presents a novel algorithm for determining the initial rotor sector and aligning the encoder with the motor while minimizing vibrations and oscillations. © 2012 Elsevier B.V. All rights reserved.


2012 - Active Filter for DC Current Components in Three-Phase Distribution Grids [Relazione in Atti di Convegno]
Barater, D.; Buticchi, G.; Franceschini, G.; Lorenzani, E.
abstract

In three-phase distribution networks non-linear loadscan give rise to DC current components. A DC currentcomponent is particularly detrimental for the distribution powertransformers, because it can lead to asymmetric magnetic coresaturation. Apart from an increased THD in line currents,transformers operating under saturation conditions presentincreased VAR absorption, and, accordingly, possible damageconsequent to the overheating. This paper proposes anelectronic system able to compensate the undesired DC currentcomponents flowing in a three-phase distribution grid. Thissystem comprehends a precise magnetic sensor and a powerconverter stage (different for low or medium-high voltage grids).The magnetic sensor detects the effects of the DC currentcomponents that flow in the power conductors, whereas thepower converter compensates them. Simulation andexperimental results show the effectiveness of the proposedsystem.


2012 - Development of synchronized control for multiple 2 MVA AC/AC converters [Relazione in Atti di Convegno]
Cova, Paolo; Franceschini, Giovanni; Toscani, Andrea
abstract

In this paper a full digital control for high performances modular power converters is developed. As a matter of fact, to increase output power, control strategy can parallel two or more power converters assuring, at the same time, optimum current sharing among them. © 2012 IEEE.


2012 - Digital Control of Actual Grid-Connected Converters for Ground Leakage Current Reduction in PV Transformerless Systems [Articolo su rivista]
Buticchi, G.; Barater, D.; Lorenzani, Emilio; Franceschini, G.
abstract

The design of a PV grid-connected converter usuallycomprehends a galvanic isolation between the grid and thephotovoltaic panels. Recently, in low power systems, thegalvanic isolation has been removed with the aim to increaseefficiency and reduce the cost of the converter. Due to thepresence of a parasitic capacitance between the photovoltaiccells and the metal frame of the PV panel, usually connected toearth, a high value of common mode current (i.e. groundleakage current) can arise. In order to limit the ground leakagecurrent (which deteriorates the power quality and generatesEMI), new converter topologies have been proposed. Theireffectiveness is based on the symmetrical (ideal) commutationsof the power switches and some of them adopt a further voltagelevel derived from a capacitive divider of the DC bus voltage.Unfortunately, in actual implementations, asymmetrical powerswitches transients and variations of this added voltage lead tohigher ground leakage current with respect to the ideal case.After a review of the state of the art this paper investigates thesetwo issues and presents a particular solution (based on digitalcontrol and PWM strategy) that, in conjunction with acompensation strategy of power switches actual commutations,guarantees low ground leakage current regardless theparameters tolerance of the power circuit. Simulation andexperimental results confirm the effectiveness of the proposedsolution.


2012 - Fault tolerant digital control of 2 MVA parallelable frequency converters for harbor applications [Relazione in Atti di Convegno]
Toscani, Andrea; Cova, Paolo; Bertoluzza, Fulvio; Pini, Nicola; Franceschini, Giovanni
abstract

This paper deals with the design of a fault tolerant digital control of high power, parallelable frequency converters for harbor application. With the aim to yield a high degree of system availability the control algorithm must be able to automatically switch from parallel to single mode operation in case of fault. Scalability is a further key feature of the proposed control strategy: in order to increase the output power rating, the control strategy can parallel more than two converters increasing, in turn, the availability of the whole system as well. An inclusive set of MATLAB simulations shows that the proposed control algorithm makes the whole power system complying with the specifications in terms of THD, power efficiency and dynamic response. A full set of measurements, performed on a scaled converter prototype, confirmed the simulation results. © 2012 IEEE.


2012 - Induction machine current space vector features to effectively discern and quantify rotor faults and external torque ripple [Articolo su rivista]
Concari, C.; Franceschini, G.; Tassoni, C.
abstract

Intensive research efforts have been spent with the aim of separating the effects of load torque unbalance from those of rotor faults in induction machines. Recent literature reports that active and reactive components of the current space vector seem to show different features in correspondence of the two fault events. This study shows the angular displacement of the above components is fundamental in order to distinguish external torque ripple from rotor faults. The fault severity and the external torque ripple can also be effectively determined. Moreover, the proposed technique allows to assess the range of validity of the usual motor current signature analysis (MCSA), based on the sum of the amplitude of stator current sidebands, for quantifying rotor bar faults. © 2012 © The Institution of Engineering and Technology.


2012 - Saturation Compensation Strategy for Grid Connected Converters Based on Line Frequency Transformers [Articolo su rivista]
Franceschini, G.; Lorenzani, Emilio; Buticchi, G.
abstract

This paper deals with the compensation of magneticsaturation in line frequency transformer coupled, grid-connectedpower converters. The developed strategy originates from thechoice of controlling the actual current injected in the grid (outputof the line frequency transformer) instead of the input current ofthe transformer, as usually proposed. As a matter of fact, betterpower quality cannot neglect the direct control of the injected gridcurrent. An effective solution providing zero steady-state error atgrid frequency and superior disturbance rejection involves the useof a d–q current controller synchronous with the grid voltage. Forthis reason, the proposed saturation compensation strategy hasbeen implemented inside the d–q reference frame. The downsideis that closing the current feedback at the transformer output rendersimpossible to control the dc current at transformer input,leading to core saturation. A core saturation compensation strategy,based only on the monitoring of the output current distortionaround voltage zero crossings, is here presented. Moreover, sincethe proposed solution does not rely on dc measures, offset problemsare avoided. Experimental results confirm the effectiveness of theproposed control architecture and of the strategy adopted to avoidtransformer core saturation.


2012 - Unipolar PWM Strategy for Transformerless PV Grid-Connected Converters [Articolo su rivista]
Barater, D.; Buticchi, G.; Crinto, A. S.; Franceschini, G.; Lorenzani, Emilio
abstract

In domestic grid-connected PV applications, a singlephase converter is usually employed. In such low-power plants, it is possible to adopt converter topologies without galvanic isolation between the photovoltaic (PV) panels and the grid. The absence of a high- or line-frequency transformer permits us to reduce power losses, cost, and size of the converter. On the other side, in the presence of a galvanic connection, a large ground leakage current could arise due to parasitic PV panel capacitance. Leakage currents cause electric safety problems, electromagnetic interference increase and, consequently, a reduction of the converter power quality. This paper presents a converter topology able to minimize the ground leakage current also in the case of unipolar pulsewidth modulation without increasing inductive common mode filter size and preserving efficiency. Simulations and experimental results show the feasibility of the proposed solution.


2011 - A DC Offset Current Compensation Strategy in Transformerless Grid-Connected Power Converters [Articolo su rivista]
Buticchi, G.; Lorenzani, Emilio; Franceschini, G.
abstract

A line frequency transformer is usually employed in grid-connected power converters, from both renewable and traditional energy sources, in order to suppress the DC current component and the ground leakage current. Solutions employing a high frequency transformer or employing no transformer at all have recently been investigated in order to reduce size, weight and cost. As a consequence, unless a suitable remedy is adopted, a DC current component exceeding the limits enforced by international standards may be injected into the grid.This paper proposes a simple and cheap solution to reduce the DC current component injected into the grid in the case of a full-bridge, single-phase, transformerless converter. The proposed strategy is intrinsically insensitive to offset measurement errors and can be utilized as a robust and dynamic offset compensator for the current transducer.The simulation results have confirmed the theoretical behavior of the proposed solution, while the experimental ones, performed for different values of output power and for different current control architectures, have shown its effectiveness.


2011 - A geometrical interpretation of current space vector components due to induction machines rotor faults [Relazione in Atti di Convegno]
Concari, Carlo; Franceschini, Giovanni; Tassoni, Carla; Toscani, Andrea
abstract

This paper presents a deep investigation on the rotor fault signatures of induction machines. Phase current and current space vector sidebands, spectral components of flux, torque and speed are analyzed as functions of inertia, load and machine size. Analytical expressions among the physical quantities, validated by simulation and experimental results, are developed using a synchronous reference frame. These expressions, together with geometrical loci showing the vector relationships among the quantities involved, allow a thorough understanding of the underlying physical phenomena. A test-bed able to realize a variable virtual inertia allows the experimental validation as well. © 2011 IEEE.


2011 - An insightful geometrical interpretation of spectral components of the physical quantities involved in induction machines rotor faults [Relazione in Atti di Convegno]
Concari, C.; Franceschini, G.; Tassoni, C.
abstract

This paper deeply investigates features of both current space vector components in rotating reference frame and stator current sidebands in case of induction motor rotor fault. Geometrical loci described by the representative phasors at pulsation 2sω and their dependence on inertia are evidenced. The link among torque ripple, speed ripple and flux angular ripple is considered as well, obtaining a thorough understanding and geometrical visualization of related physical phenomena. © 2011 IEEE.


2011 - Induction drive health assessment in DSP-based self-commissioning procedures [Articolo su rivista]
Concari, Carlo; Franceschini, Giovanni; Tassoni, Carla
abstract

This paper investigates the effect of different asymmetries on the results of the usual self-commissioning procedures for induction drives, as well as the further possibilities given by a digitally controlled inverter. It is shown that, even at a standstill, it is possible to detect some fault conditions of the machine. In particular, a specific supply scheme is proposed that, through the machine response, allows outlining the rotor conditions. This technique implements the IEEE Standards single-phase rotor test on a DSP-controlled converter, allowing the detection and the quantification of the rotor fault conditions. © 2010 IEEE.


2011 - Toward practical quantification of induction drive mixed eccentricity [Articolo su rivista]
Concari, Carlo; Franceschini, Giovanni; Tassoni, Carla
abstract

As far as industrial applications of induction drives are concerned, one of the most critical issues is the statement of acceptable mixed eccentricity degree and of other mechanical abnormal conditions. These troubles cause characteristic spectral components in several drive quantities, but for the sake of economy, monitoring the electrical quantities involved in drive control is preferable. Among them, current signals (i.e., motor current signature analysis) are the signals of choice for assessing the machine conditions, although no analytical link between the current signature and the eccentricity degree through machine parameters has ever been presented. Each trouble produces spectral lines at typical frequencies in the stator current: monitoring them is a usual procedure, but the threshold to discern acceptable intrinsic defects from alarming situations is hardly defined. This paper presents the formulation of a mixed eccentricity index developed through the interaction between static and dynamic eccentricities on stator windings and rotor cage. The index can be computed by a no- or mild-load test without spectral resolution problems, and it does not require any preliminary knowledge of machine health conditions. © 2011 IEEE.


2010 - A MCSA procedure to diagnose low frequency mechanical unbalances in induction machines [Relazione in Atti di Convegno]
Concari, C.; Franceschini, G.; Tassoni, C.
abstract

Intensive research efforts have been focused on the Motor Current Signature Analysis (MCSA) in order to determine the actual health conditions of induction machines. However, particular mechanical load conditions such as low frequency load torque oscillation have effects similar to rotor faults in the current spectrum and the result of diagnostic procedure may be ambiguous. A procedure based on the specific features of the current space vector in correspondence of load torque oscillation is proposed. By this way the MCSA is able to discern this kind of trouble from rotor faults and to quantify the unbalance. ©2010 IEEE.


2010 - A novel compensation strategy of actual commutations for ground leakage current reduction in PV transformerless converters [Relazione in Atti di Convegno]
Buticchi, G.; Franceschini, G.; Lorenzani, Emilio; Barater, D.; Fratta, A.
abstract

The design of a PV grid-connected converter usually comprehends a galvanic isolation between the grid and the photovoltaic panels. Recently, for low power applications, the galvanic isolation has been removed with the aim to increase efficiency and reduce the cost of the converter. Due to the presence of a parasitic capacitance between the photovoltaic cells and the metal frame of the PV panel, usually connected to earth, a high value of common mode current (i.e. ground leakage current) can arise. In order to limit the ground leakage current (which deteriorates the power quality and generates EMI), new converter topologies have been proposed. This paper deals with a particular topology that, working in conjunction with a compensation strategy of power switches actual commutations, can guarantee low ground leakage current regardless the parameters tolerance of the power circuit. Simulation and experimental results confirm the effectiveness of the proposed solution.


2010 - A novel five-level single phase grid connected converter for renewable distributed systems [Relazione in Atti di Convegno]
Buticchi, G.; Franceschini, G.; Lorenzani, Emilio
abstract

In low-power grid connected systems (renewable or traditional energy sources) a single phase converter is usually adopted. In order to reduce losses, costs and size the keyword is removing any kind of transformer. This paper deals with a novel five level converter topology that follows this trend. The proposed converter architecture is based on a full bridge topology with two more power switches and two diodes connected to the midpoint of the DC link. Since the two added levels are obtained by the discharge of two capacitors, the balancing of the midpoint voltage is taken into account. Simulation and experimental results show the effectiveness of the proposed solution.


2010 - Compensation of magnetic core saturation for grid connected single-phase power converters [Relazione in Atti di Convegno]
Franceschini, G.; Lorenzani, E.; Bellini, A.; Fratta, A.
abstract

This paper proposes a saturation compensation strategy for single phase grid-connected power converters based on line frequency transformer. High power quality operations requires the direct control of injected grid current providing zero steady-state error at grid frequency. A zero steady-state error at grid frequency can be obtained by a control in a synchronous reference frame that ensures an infinite open loop gain at fundamental frequency and a superior disturbance rejection. However, the direct control of grid current is archived providing that transformer core saturation is avoided. Since the transformer blocks out the DC components the feedback loop closed on the transformer output current can lead to core saturation. This paper presents a compensation strategy based only on the monitoring of the output current distortion around voltage zero crossings. The proposed solution is free from offset problems, since no DC measurement is required. Experimental results confirm the effectiveness of the proposed control architecture and of the strategy adopted to avoid transformer core saturation. ©2010 IEEE.


2010 - Compensation strategy of actual commutations for PV transformerless grid-connected converters [Relazione in Atti di Convegno]
Buticchi, G.; Franceschini, G.; Lorenzani, E.
abstract

Photovoltaic grid-connected converters usually embed a high-frequency or a line transformer, which guarantees galvanic isolation between the photovoltaic field and the mains. In order to increase efficiency and reduce the total cost of the system, the transformer has been removed, and special topologies of converter have been studied in order to limit the ground leakage current that arises with the galvanic connection. In fact, the parasitic capacitance between the photovoltaic cells and the metallic frame of the panel allows high ground leakage current (i.e. common mode current) to be injected into the grid. Actual solutions rely heavily on the symmetry of the system to address the problem. This paper presents a novel strategy to compensate for non-ideal switching behavior of power devices, which is immune to layout asymmetries and tolerance of parameters. Simulation results show the feasibility of the proposed solution. ©2010 IEEE.


2010 - Discerning mechanical load unbalances from rotor faults in induction machines through current space vector components [Relazione in Atti di Convegno]
Concari, C.; Franceschini, G.; Tassoni, C.
abstract

Low frequency load torque oscillations and rotor faults have similar effects on stator current spectral contents of induction machines. Intensive researches efforts have been spent with the aim of separating them through Motor Current Signature Analysis (MCSA). So far, however, the proposed techniques are impractical because they need an accurate estimation of the machine parameters. In this paper a procedure to discern the two kinds of events, based on the unique features of the current space vector, is proposed. By this procedure, MCSA can be safely used to diagnose rotor faults. © 2010 IEEE.


2010 - Discussion of "A new criterion for the quantification of broken rotor bars in induction motors" [Articolo su rivista]
Tassoni, C.; Filippetti, F.; Franceschini, G.
abstract

The paper proposes an improvement on the motor current signature analysis diagnostic procedure for induction machines broken rotor bars detection. The procedure, referred to as the “Filippetti criterion” in the paper, is based on the sum of the sidebands amplitude [1].


2009 - A new proposal for ground leakage current reduction in transformerless grid-connected converters for photovoltaic plants [Relazione in Atti di Convegno]
Barater, D.; Buticchi, G.; Crinto, A.; Franceschini, G.; Lorenzani, Emilio
abstract

In domestic grid connected PV applications a single phase converter is usually used. In such a low power plants it is possible to adopt converter topologies without galvanic isolation between the photovoltaic panels and the grid. The absence of a high or low frequency transformer permits to reduce power losses, cost and size of the converter. On the other side in presence of a galvanic connection a large ground leakage current could arise due to parasitic PV panel capacitance. Leakage currents cause electric safety problems, EMI increase and, consequently, a reduction of the converter power quality. This paper presents a converter topology able to minimize the ground leakage current also in case of unipolar PWM modulation without increasing inductive common mode filter size and preserving efficiency. Simulations and experimental results show the feasibility of the proposed solution.


2009 - A novel current sensing DC offset compensation strategy in transformerless grid connected power converters [Relazione in Atti di Convegno]
Buticchi, G.; Franceschini, G.; Lorenzani, Emilio; Tassoni, C.; Bellini, A.
abstract

In grid connected power converters both from renewable or traditional energy sources a line frequency transformer is usually employed in order to suppress the DC component. Recently, solutions based on a high frequency transformer or without transformer, usually referred as transformerless, are being investigated in order to reduce size, weight and costs. As a consequence, unless a suitable remedy is adopted, a DC component, that might overcome limits forced by international standards, may appear. This paper proposes a simple and cheap solution to reduce the DC current component injected into the grid in case of a full-bridge, single phase, transformerless converter. The proposed strategy is intrinsically insensitive to offset measurement errors and can be utilized as a robust and dynamic offset compensator for the Hall effect sensor mostly used as current transducer. Experimental results, performed for different current values and for different current control architectures, show the effectiveness of the proposed solution.


2009 - Distributed cogeneration plants [Articolo su rivista]
Bellini, Alberto; Franceschini, G.; Lorenzani, Emilio; Tassoni, C.
abstract

This article proposes a new control scheme for a distributed cogeneration (microcogeneration) plant using a three-phase induction machine as an electric generator. This control scheme assures a better energy-conversion quality. The plant can be operated as a grid-connected generator with load tracking or as an isolated generator. In isolated operation, the induction generator is excited with a current-controlled voltage source inverter (CCVSI) having a suitable capacitive bank in the dc side. During grid-connected operations, the same converter can be used for power factor correction. Energy generation and its optimal use are the key issues in actual social conditions. In this framework, the European Union (EU) anticipates that the amount of energy produced by cogeneration plants will double within five years, and this might be an underestimated growth, as its potential is still unexploited. Cogeneration or combined heat and power (CHP) means the combined production ofthermal, electrical, and mechanical energy.Recently, distributed cogeneration or micro-CHP was constantly in the spotlight of the industrial and scientific community.


2009 - Hybrid architectures for EMC mitigation of switching audio amplifier [Relazione in Atti di Convegno]
Bellini, A.; Boccedi, V.; Franceschini, G.; Lorenzani, Emilio; Montanari, I.; Tacchini, A.
abstract

In this article are discussed some meaningful issues concerning the measurement of radiated emissions generated by standard and hybrid architectures amplifiers. These measurements aimed to compare different levels of radiated emission for architectures also related to different environments.


2009 - Monitoring of rotor cage conditions in induction machines by instantaneous reactive power and current space vector's reactive component [Relazione in Atti di Convegno]
Concari, C.; Franceschini, G.; Tassoni, C.
abstract

Intensive research efforts have been focused on the Motor Current Signature Analysis (MCSA) in order to detect rotor condition of induction machines. The interpretation of the single-phase current spectrum provides direct information on the presence of abnormal conditions, while their quantification is an open problem as signature spectral lines depend also on motor load and inertia. Recently the attention has been focused on the reactive part of the instantaneous power: its spectrum shows a 2sw component related to the fault severity that might improve the diagnosis. The aim of this paper is the performance evaluation of this diagnostic index to state the rotor breakage severity in induction machines. It is shown that instantaneous current components bear the same features as instantaneous power components. Moreover, it is possible to switch from amplitudes and angular displacements of reactive and active current components to the (1±2s)w sidebands and therefore to verify the link among torque ripple, speed ripple, flux and current components. © 2009 IEEE.


2009 - Self-commissioning procedures to detect parameters in healthy and faulty induction drives [Relazione in Atti di Convegno]
Concari, C.; Franceschini, G.; Tassoni, C.
abstract

Different automatic procedures to estimate induction machines parameters, known as self-commissioning, can be found in literature. They usually involve supplying a single phase or two series-connected phases. An ideal machine should present the same behavior at all terminals, while in an actual machine non-idealities alter the response to the signals. Some techniques to state machine condition during self-commission procedures based on the parameter values discrepancies or on the response to particular signals injected have been proposed. This paper investigates the effect of the different asymmetries on the usual self-commissioning procedures and the further possibilities given by the machine supply through the digitally controlled inverter. It is shown that, even at standstill, it is possible to detect and state the severity of some fault conditions of the machine. In particular a specific supply voltage signal is proposed that, through the machine response, outlines the machine rotor conditions. © 2009 IEEE.


2009 - Towards practical quantification of induction drives mixed eccentricity [Relazione in Atti di Convegno]
Concari, Carlo; Franceschini, Giovanni; Tassoni, Carla
abstract

As far as industrial applications of induction drives are concerned, one of the most critical issues is the statement of acceptable mixed eccentricity degree and of other mechanical abnormal conditions. These troubles cause characteristic spectral components in many drive quantities, but for economic reasons the electrical quantities, already sensed for drive control purposes, are preferable; among them current signals (i.e. MCSA) are the electric signals of choice to detect the machine conditions. Each trouble produces spectral lines at typical frequencies in the stator current: monitoring them is a usual procedure but the threshold to discern acceptable intrinsic defects from alarming situations is hardly defined. This paper presents an attempt to formulate a mixed eccentricity index developed through the interaction between static and dynamic eccentricity on stator windings and rotor cage. The index can be detected by a no-load test without any spectral resolution problem and it does not require any preliminary knowledge of machine health condition. © 2009 IEEE.


2009 - Unipolar PWM for transformerless grid-connected converters in photovoltaic plants [Relazione in Atti di Convegno]
Barater, D.; Franceschini, G.; Lorenzani, Emilio
abstract

In domestic grid connected PV applications a single phase converter is usually used. In such a low power plants it is possible to adopt converter topology with no galvanic isolation between the photovoltaic panels and the grid. The absence of a high or low frequency transformer permits to reduce power losses, cost and size of the converter. On the other side in presence of a galvanic connection a large leakage ground current could arise due to parasitic PV panel capacitance. This leakage current causes electric safety problems, an increase of EMI and a reduction of the power quality. This paper presents a converter topology based on unipolar PWM modulation able to minimize the leakage ground current locking the common output voltage to VDC/2 as the converters topology based on bipolar modulation do. Simulation results show the effectiveness of the proposed topology. Eventually a comparison of the power losses of the proposed architecture with respect to some established topologies is presented.


2009 - Vibrationless alignment algorithm for incremental encoder based BLDC drives [Relazione in Atti di Convegno]
Concari, Carlo; Franceschini, Giovanni; Toscani, Andrea
abstract

Incremental encoder based BLDC drives are widely employed in industry whenever smooth and efficient operation is needed in the whole speed range. Their weak spot lies in the need for a phase of initial alignment. Such task is traditionally performed by forcing the motor through a series of fixed phase supply configurations, causing strong vibrations which can be intolerable for certain applications. In this paper a novel algorithm that allows determining the initial rotor position (sector) and aligning the encoder while minimizing vibrations and oscillations is presented. © 2009 IEEE.


2009 - “Single-Phase Grid Connected Converters for Photovoltaic Plants”, in Renewable energy [Capitolo/Saggio]
Lorenzani, Emilio; Franceschini, G.; Bellini, Alberto; Tassoni, C.
abstract

Among renewable energy sources photovoltaic systems are one of the most up to date solutions. However their diffusion is limited by relatively high cost in comparison with traditional energy sources. The downward tendency in the price of the PV (Photovoltaic) modules, together with their increasing efficiency, put solid-state inverters under the spot lights as the enabling technology for integrating PV systems into the grid.This chapter will analyze the single-phase grid connected converter usually used in PV domestic rooftop applications.There are two mandatory tasks in grid connected PV systems: the maximization of the energy extracted from the PV panels (1) and the use of a high efficiency topology for the power converter able to inject only active current into the grid (2), i.e. a pure sinusoidal current in phase with the grid voltage.


2008 - 3boost: A High-Power Three-Phase Step-Up Full-Bridge Converter for Automotive Applications [Articolo su rivista]
Franceschini, Giovanni; Lorenzani, Emilio; Cavatorta, Matteo; Bellini, Alberto
abstract

This paper describes a simple dc–dc step-up converter topology for switch-mode dc power supplies. The proposed configuration is well suited for high-power applications with battery supply. In the automotive framework, the push–pull architecture is the most widespread. However, as power increases, the use of a full-bridge architecture is mandatory. This paper presents a full-bridge architecture where the traditional single-phase transformer is replaced by a three-phase transformer. A prototype was realized and tested for the power supply of automotive devices. In this environment, one of the most important requirements is the ability to provide a burst of power during short-duration events, together with high-efficiency and high-quality output voltage. The latter constraints can be achieved by only using closed-loop switch-mode dc–dc converters at high switching frequency, thus reducing converter efficiency and creating electromagnetic- compatibility (EMC) problems. In this paper, the aforementioned issues were tackled relying on an open-loop topology. Open-loop converters are feasible if the output resistance of the converter is as low as possible, and a possible solution is the minimization of power losses. The solution is the use of a three-phase transformer with a delta-wye connection within a full-bridge converter topology. The configuration will be referred to as 3boost power supply. The three-phase transformer replaces the common single-phase transformer, and it is driven by a three-phase full-bridge inverter operating in six-step modulation. At secondary, a three-phase full wave diode rectifier is used to obtain the output dc voltage level. Therefore, a unitary transformer utilization factor is achieved. A simple theoretical comparison between the three types of converter: push–pull, conventional full bridge, and 3boost is shown. A low-power version of the converter was realized. Experiments confirm that this topology allows to achieve a high efficiency, a lower ripple factor, and a good EMC behavior.


2008 - Comparative analysis of CHCP systems based on solar energy [Relazione in Atti di Convegno]
Immovilli, Fabio; Bellini, Alberto; Bianchini, Claudio; Rossi, Andrea; Franceschini, G.
abstract

The combined production of heating, cooling and electricity (CHCP) or trigeneration in a grid-connected energy market may become profitable with respect to traditional systems, where electricity, heat, and cooling are produced or purchased separately. Namely, the use ofsolar energy as a primary energy source can lead to a substantial improvement, overcoming many of the traditional drawback associated with micro-cogeneration and trigeneration.So doing a CHCP system with renewable energy sources is realized, that is an attractivesolution for domestic needs, provided that a cost-effective technical solution is available.This paper reviews and compares CHCP system and technologies based on solar energy.


2008 - Differential diagnosis based on multivariable monitoring to assess induction machine rotor conditions [Articolo su rivista]
Concari, Carlo; Franceschini, Giovanni; Tassoni, Carla
abstract

Multivariable supervision systems for online monitoring of induction motors allow large versatility and diagnosis robustness. As regards rotor faults, the diagnostic procedure based on sideband current components may fail due to the presence of interbar currents that reduce the degree of rotor asymmetry and, thus, the amplitude of these spectral components. On the other hand, the interbar currents produce core vibrations in the axial direction; these vibrations can be detected using a suitable vibration sensor. In this paper, a differential fault analysis based on traditional motor current signature analysis (MCSA) and on radial and axial vibration monitoring is proposed to discern cases in which the presence of interbar currents decreases the sensitivity of MCSA. The features of stator currents and of radial and axial core vibration signals are investigated in order to increase the reliability of the diagnostic system. Moreover, to explore the possibility of obtaining further information, stray flux signals are taken into account. © 2008 IEEE.


2008 - Hybrid-Electric Vehicles for advanced urban mobility: A new proposal [Relazione in Atti di Convegno]
Concari, C.; Franceschini, G.; Toscani, A.
abstract

Hybrid-Electric Vehicles (HEVs) are currently a hot research topic in the field of clean and sustainable mobility. HEVs can make a difference especially in urban areas where, due to the typical driving patterns with frequent stops and standing starts, traditional internal combustion engines (ICEs) operate at very low levels of efficiency. The authors believe that personal urban mobility is the automotive segment that, more than others, can reap on the benefits of hybrid traction. This paper presents the design and optimization of a small HEV for personal urban mobility, with a particular focus on the optimization of the electric powertrain. © 2008 IEEE.


2008 - Quantitative design of Active Control for Self Excited Induction Generators in Grid Isolated Operation [Relazione in Atti di Convegno]
Bellini, Alberto; Franceschini, G.; Lorenzani, Emilio; Tassoni, C.
abstract

The use of induction machines as electric generator with renewable energy sources is fostered by its simple connection to the power grid, and by its intrinsic safety. In grid isolated operation the induction generator requires a proper excitation. A suitable machine excitation can be achieved relying on a Current Controlled Voltage Source Inverter (CC-VSI) with a proper capacitors bank in the DC side. In this way, higher efficiency, higher control dynamic and a very robust behavior in case of transient variation of the prime mover speed is accomplished. A suitable capacitors bank is still used on the AC side, in order to reduce the ratings of the CC-VSI and to avoid pre-charging. This paper presents the quantitative design of the CC-VSI and of capacitors bank used for the power management in grid isolated operation. The aim is to achieve the minimum ratings doing to operate the CC-VSI in two quadrants. The quantitative procedure starts from the load requirements that lead to the choice of induction generator. Laboratory experimental results, obtained by an air-gap flux field oriented control, show good behaviors both in transient and in steady state conditions.


2008 - Solar trigeneration for residential applications, a feasible alternative to traditional micro-cogeneration and trigeneration plant [Relazione in Atti di Convegno]
Immovilli, Fabio; Bellini, Alberto; Bianchini, Claudio; Franceschini, G.
abstract

Trigeneration stands for the combined production of electricity, heat, and cooling (CHCP).This paper reviews and compares CHCP system based on solar energy with respect to traditional CHCP ones.A further comparison is made among the possible technologies for solar CHCP to assess the technical solutions more suited to residential applications. Beyond photovoltaic based systems, two other solutions are proposed: a concentrated sunlight all-thermoacoustic system and an hybrid thermo-photovoltaic system.In a grid-connected energy market, the adoption of CHCP plants may become profitable with respect to traditional systems, where the single energies are produced or purchased separately. Specifically, the onset of solar trigeneration can lead to a substantial improvement, overcoming many of the traditional drawback associated with micro-cogeneration and trigeneration.The result is a trigeneration system based totally on renewable energy. This is especially attractive for the residential demand, provided that a cost-effective technical solution is available.


2008 - Synchronous reference frame grid current control for single-phase photovoltaic converters [Relazione in Atti di Convegno]
Bellini, Alberto; Franceschini, G.; Lorenzani, Emilio; Tassoni, C.
abstract

This paper proposes a high performance control in a synchronous reference frame for a single-phase grid connected converter. The proposed control allows to obtain easily an infinite control loop gain at fundamental frequency and a superior disturbance rejection. So doing only active current is injected in the grid thus achieving maximum conversion efficiency and decreasing current distortion.The control has been implemented in a single-stage converter for single-phase PV systems. The converter is a standard full-bridge three-level voltage source inverter that delivers a sinusoidal current to the grid through an inductive filter and a line frequency isolation transformer. The presence of the transformer block out the DC components injected in the grid but the current feedback, closed around the output of the transformer, can lead to core saturation. To avoid saturation a compensation strategy has been developed relying on output current distortion in correspondence of voltage zero crossings. Simulation and experimental results confirm the effectiveness of the proposed control architecture and of the strategy adopted to avoid transformer core saturation.


2007 - Different Procedures for the Diagnosis of Rotor Fault in Closed Loop Induction Motors Drives [Relazione in Atti di Convegno]
Bellini, Alberto; Concari, C; Franceschini, G; Tassoni, C.
abstract

This paper deals with different procedures that can be applied to diagnose the severity degree of rotor faults in closed loop controlled induction machines. A solution based on field oriented control (FOC) was investigated in order to validate the robustness of the diagnostic procedures towards the regulator parameters. Different diagnostic procedures were investigated, that rely on different diagnostic indexes. Specifically a few electric quantities are considered as possible fault alert signals: the spectral analysis of manipulated and controlled variables, the voltage homopolar components (voltage zero sequence), and the spectral analysis of motor input current due to a high frequency voltage injection. It turns out that the last quantity is a simple and effective index able to detect and quantify the fault severity degree. The procedures based on the above mentioned quantities are validated by experiments made with a DSP based current controlled voltage source inverter (CCVSI) supplying an induction machine with three rotors in different health conditions.


2007 - High dynamic control of a stepper motor for textile applications [Relazione in Atti di Convegno]
Bellanova, R; Bellini, Alberto; Lorenzani, Emilio; Franceschini, G; Tassoni, C; Toscani, A.
abstract

Textile applications require peculiar specifications in terms of accuracy and speed from drives. In this paper a high dynamic control for a linear drive was realized. A vector control for a magnetic disc stepper motor was realized that allows huge linear acceleration and accurate speed control.


2007 - Mixed-Mode PWM for High-Performance Stepping Motors [Articolo su rivista]
Alberto, Bellini; Concari, C.; Franceschini, G.; Toscani, A.
abstract

This paper describes the realization of a high performance drive based on stepping motors, with specific reference to the optimal choice of pulse width modulation (PWM). An original modulation technique is proposed that allows, in conjunction with current feedback, to achieve high performances together with a reduced current ripple. A prototype DSP based drive was realized for a small size stepping motor.


2007 - Severity assessment of rotor faults in closed loop induction drives by different approaches [Relazione in Atti di Convegno]
Concari, C.; Franceschini, G.; Lorenzani, E.; Tassoni, C.; Toscani, A.
abstract

In this paper different procedures are validated to diagnose and assess the severity degree of rotor faults in closed loop controlled induction machines. The possible diagnostic indexes are investigated through spectral analysis of manipulated and controlled variables. Common control schemes have been considered to evaluate the diagnostic robustness towards operating condition and regulator parameters. Voltage injection was considered as well as a possible tool for diagnostics by analyzing the amplitude of spectral lines arising in motor input current spectrum. Experimental results guide the selection of suitable analytical models for the faulty machine. The experiments are obtained with a DSP based Current Controlled Voltage Source Inverter (CCVSI) supplying a 1.5 kW induction machine in which three different rotors differing in asymmetry degree were used. ©2007 IEEE.


2007 - Torque and Field Currents Peculiarities Under Different Induction Machine Troubles [Relazione in Atti di Convegno]
Concari, C; Franceschini, G; Tassoni, C; Bellini, Alberto
abstract

Motor current signature analysis (MCSA) is a method usually adopted to detect troubles in induction machines. However misunderstandings can be found about the mechanisms linking the anomalies to the current spectrum components. To improve the comprehension of these mechanisms a rotor flux observer to compute field current and torque current is proposed. Input currents and voltages and mechanical speed are the signals taken into account for the computation. The effects of mechanical unbalance and of mixed eccentricity and then the effect of a rotor asymmetry are considered. For the experiments a machine presenting an intrinsic rotor asymmetry and an intrinsic mixed eccentricity is utilized. A mechanical unbalance and an artificial increment of mixed eccentricity are introduced. The peculiarities of the considered variables due to the different troubles and their dependence on machine load are evidenced.


2006 - Current-controlled shape memory alloy actuators for automotive tumble flap [Relazione in Atti di Convegno]
Colli, M.; Bellini, A.; Concari, C.; Toscani, A.; Franceschini, G.
abstract

Mechatronics devices are becoming a mandatory option in the automotive framework, as high integration and low weight are common requirements for most applications. To this aim non-electric drives are being investigated. An attractive option is the use of Shape Memory Alloy (SMA) actuation technology that allows achieving a very high power/weight ratio for light and small actuators. Feasibility studies were made to show the potential of SMA as actuators. This paper proposes the application of a SMA actuator for automotive tumble flaps. A critical comparison between traditional and SMA actuators is presented, and the attention is focused on the power converter used to "drive" the SMA. Experiments were made on a prototype realized for angular control of tumble flaps of an air intake manifold for internal combustion engines that allows achieving better gas combustion and higher performances. The proposed control scheme includes a current feedback that allows a sensorless control position for the tumble shaft. ©2006 IEEE.


2006 - Field Oriented Control of Self-Excited Induction Generator for Distributed Cogeneration Plants [Relazione in Atti di Convegno]
Bellini, Alberto; Franceschini, G.; Lorenzani, Emilio; Tassoni, C.; Tomaiuolo, M.
abstract

This paper deals with the control of a distributedcogeneration (micro-cogeneration) plant using a three-phaseinduction machine as electric generator. The plant can beoperated as a grid connected generator with load tracking or asisolated generator. In isolated operation the induction generatoris excited with a Current Controlled Voltage Source Inverter(CCVSI) with a suitable capacitive bank in the DC side. Duringgrid connected operation the same converter can be used forpower factor correction.The control scheme relies on air-gap flux field oriented controlbased on ADMC401 DSP. A better energy conversion quality isachieved thanks to the control of the exciting current component.This allows to obtain higher efficiency, higher control dynamicand a very robust behaviour in case of transient variation of theprime mover speed.


2006 - Modelling of a Parallel Hybrid Power Audio Amplifier [Relazione in Atti di Convegno]
Bellini, A.; Chiesi, L.; Lorenzani, Emilio; Franceschini, G.
abstract

Parallel audio amplifier are hybrid amplifiers thatcouple a linear and a switching stage with a parallel connection. Aproper control must be designed so that the voltage is controlledby the linear stage, while most of the current is driven by theswitching stage. So doing the overall architecture achieves thetypical efficiency of the switching stage and the distortion of thelinear stage. In summary a nice trade-off between efficiency anddistortion can be achieved, allowing to reduce heat dissipationkeeping a pleasant sound reproduction.The above purposes can be achieved only with a proper controlthat must set accurately the balance between the two stages, andits implementation is very critical. The paper deals with the modelof the hybrid audio amplifier architecture aiming at retriving themost critical items, and at defining simple relationships for theoptimal design of the amplifier.A prototype hybrid amplifier was realized, that confirms theeffectiveness of the proposed method.


2006 - Monitoring of induction machines by maximum covariance method for frequency tracking [Articolo su rivista]
Alberto, Bellini; Franceschini, G.; Tassoni, C.
abstract

Several techniques were presented in the literature in order to perform accurate tracking of frequencies for different purposes. Most of them are modified versions of the traditional discrete Fourier transform (DFT) or other spectrum-estimation techniques. This paper presents a procedure based on the statistical analysis of the current signal in the time domain, referred to as maximum covariance method for frequency tracking (MCMFT), which allows to obtain high-frequency resolution independent of the sampling frequency and of the time acquisition period. Owing to the proposed procedure, the spectrum lines related to supply frequency or to rotor-slotting frequency for an induction machine can be detected with extreme accuracy within a wide range of sampled data conditions. Then, an accurate slip computation, or speed estimation, for sensorless control or distribution network diagnosis can be performed. Comparisons between previously existing methods and the proposed one are reported, in order to critically analyze its performances. Two different-sized induction machines were used for the experiments.


2006 - Thorough Understanding and Experimental Validation of Current Sideband Components in Induction Machines Rotor Monitoring [Relazione in Atti di Convegno]
Bellini, Alberto; Concari, C.; Franceschini, G.; Lorenzani, Emilio; Tassoni, C.; Toscani, A.
abstract

The MCSA diagnostic procedures for the rotordiagnosis of induction machines are mostly based on thesideband lines near the supply frequency line that appear inthe input current spectrum. The left component (1-2s)f is theeffect of rotor backward rotating field caused by the cagerotor asymmetry and it varies with the asymmetry degree andwith the rotor current, i.e. with the machine load.The right component (1+2s)f is caused by the speed ripplecreated by the left component, being the combined machineloadinertia the main parameter that spreads the asymmetryeffect into the two sideband components.Theoretically it can be shown that the sum of the twocomponents is not affected by the speed ripple effect andtherefore this sum may be used as an effective diagnosticindex to state rotor conditions.The above results can be experimentally validated only once asuitable test set-up is realized that allows changing the inertiavalue. To this aim a test bed was designed so that the virtualinertia of the mechanical system can be chosen by the user.This allows to prove the theoretical claims and to obtain athorough understanding about the effect of inertia onsideband components, improving the performance of rotorcondition monitoring techniques.


2006 - Vibrations, currents and stray flux signals to asses induction motors rotor conditions [Relazione in Atti di Convegno]
Alberto, Bellini; Concari, C.; Franceschini, G.; Tassoni, C.; Toscani, A.
abstract

Multi-variable monitoring systems for on-line monitoring of induction motors allow larger versatility and robustness. In case of rotor faults, the diagnostic procedure based on sideband current components may fail for the presence of inter-bar currents that reduce the amplitudes of these components. On the other hand the inter-bar currents modify the core vibration; therefore the analysis of both line currents and core vibration signals may increase the effectiveness of the diagnostic procedure. In this paper the features of stator currents and core vibration signals are investigated in order to achieve an accurate and reliable diagnostic system. Moreover stray flux signals are considered to explore the possibility of obtaining further information. ©2006 IEEE.


2005 - Battery choice and management for New Generation Electric Vehicles [Articolo su rivista]
Affanni, A.; Bellini, Alberto; Franceschini, G.; Guglielmi, P.; Tassoni, C.
abstract

Different types of electric vehicles (EVs) have been recently designed with the aim of solving pollution problems caused by the emission of gasoline-powered engines. Environmental problems promote the adoption of new-generation electric vehicles for urban transportation. As it is well known, one of the weakest points of electric vehicles is the battery system. Vehicle autonomy and, therefore, accurate detection of battery state of charge (SoC) together with battery expected life, i.e., battery state of health, are among the major drawbacks that prevent the introduction of electric vehicles in the consumer market. The electric scooter may provide the most feasible opportunity among EVs. They may be a replacement product for the primary-use vehicle, especially in Eu- rope and Asia, provided that drive performance, safety, and cost issues are similar to actual engine scooters. The battery system choice is a crucial item, and thanks to an increasing emphasis on vehicle range and performance, the Li-ion battery could become a viable candidate. This paper deals with the design of a battery pack based on Li-ion technology for a prototype electric scooter with high performance and autonomy. The adopted battery system is composed of a suitable number of cells series connected, featuring a high voltage level. Therefore, cell equalization and monitoring need to be provided. Due to manufacturing asymmetries, charge and discharge cycles lead to cell unbalancing, reducing battery capacity and, depending on cell type, causing safety troubles or strongly limiting the storage capacity of the full pack. No solution is available on the market at a cheap price, because of the required voltage level and performance, therefore, a dedicated battery management system was designed, that also includes a battery SoC monitoring. The proposed solution features a high capability of energy storing in braking conditions, charge equalization, overvoltage and undervoltage protection and, obviously, SoC information in order to optimize autonomy instead of performance or vice-versa.


2005 - Induction Drives Diagnosis by Signal Injection: Effectiveness and Severity Classification [Relazione in Atti di Convegno]
Bellini, A.; Concari, C.; Franceschini, G.; Lorenzani, Emilio; Tassoni, C.
abstract

The “signal injection technique” introduced torealize speed sensorless induction drive exploiting rotorasymmetry effects, is an attractive procedure for diagnosticpurposes as well. At first it was proposed as alternative techniqueto detect rotor damage, then its use has been extended to statorshort circuit detection. An important issue is the possibility tostate the fault severity, linking the amplitude of the novel spectralcomponents induced by the injected signal to the fault entity,avoiding the dumping action of the regulator.In this paper the signal injection technique for rotor barbreakage diagnosis and stator short circuit detection isinvestigated and compared with the classical MCSA procedures.Simple machine models are presented that allow to staterelationships between the fault entity and the amplitude ofspecific spectrum lines in stator current or current space vector.Experiments and theoretical analysis show that for brokenbars this technique has some advantages with respect to MCSA.On the contrary in case of stator short circuits the signalinjection techniques is not suitable for diagnostic purposes, beingthe specific line amplitude only partially affected by the fault.


2004 - 3boost a High Power Three Phase Step-up Full-bridge Converter for Automotive Applications [Relazione in Atti di Convegno]
Franceschini, G.; Lorenzani, Emilio; Bellini, A.; Cavatorta, Marco
abstract

This paper presents a simple and original DC-DCstep-up converter topology for switchmode DC powersupplies. The proposed architecture is well suited for highpower applications with battery supply.A prototype was realized and tested for the power supply ofautomotive devices. In this environment signals arecharacterized by high dynamic variations, thus ihey can beoperated only relying on power supplies with high dynamiccapabiliiies. The latter constraint can be SChieVed only usingdosed-loop switch-mode DUDC converters at high switchingfrequency. So doing converter efficiency is reduced, and EMCproblems arise. In summary power supply efficiency andsupply voltage quality are key Ceatures of the converler design.In lhis paper the above mentioned issued were tackledrelying on an open loop topology. The original solution is theadoption of a three-phase transformer with delta-wyeconnection within a full-bridge converter topology. Theproposed architecture will be referred to as 3boost powersupply. The three-phase transformer replaces the commonsingle-phase transformer and it is supplied at primary by threesquare waves, produced by a three-phase full bridge inverter.At secondary a three-phase full wave diode rectiller is used toobtain the output DC voltage level.The proposed architecture is patent pending.


2004 - Mixed mode PWM for high performance stepping motors [Relazione in Atti di Convegno]
Bellini, Alberto; Concari, C.; Franceschini, G.; Toscani, A.
abstract

This paper describes the realization of a high performance drive based on stepping motors, with specific reference to the optimal choice of PWM modulation. An original modulation technique is proposed that allows to achieve high performances together with a reduced current ripple. A prototype DSP based drive was realized for a small size stepping motor. © 2004 IEEE.


2003 - Design of a high speed induction motor sensorless drive based on admcf341 dsp controller [Relazione in Atti di Convegno]
Franceschini, G.; Lorenzani, Emilio; Tassoni, C.; De Mari, Y.
abstract

A low-cost, high reliability drive without mechanical sensor is described. The application concerns awash machine system that, in spite of the simple, but effective solution, implemented in a fixed pointDSP, presents a good dynamic performance and good steady-state speed accuracy in a very wideoperating speed range.Motor phase current reconstruction is performed suitably sampling the voltage across three shuntresistances put in series to the IGBT emitters while, as far as phases voltage measurement isconcerned, bus voltage is sampled and then motor phase voltages are reconstructed inside the DSPusing PWM duty cycle and dead-time correction strategy.Drive performances, as far as torque production is concerned, have been tested using a dynamometerin a speed range up to 12000 rpm and compared with the torque produced with the usual constant Voltper Hertz (V/f) method. The proposed sensorless control in spite of hardware simplicity that,obviously, translates in low cost, comparable with the open loop solution, presents superior dynamicalperformances, higher torque per ampere, and then efficiency.


2003 - EV Battery State of Charge: Neural Network Based Estimation [Relazione in Atti di Convegno]
Affanni, A.; Concari, C.; Franceschini, G.; Lorenzani, Emilio; Tassoni, C.; Bellini, Alberto
abstract

Different Electric Vehicles (EV) types have beenrecently developed with the aim of solving pollution problemscaused by the emission of gasolinepowered engines.Environmental Considerations promote the adoption 01 EV forurban transportation. As it is well known one of the weakestpoints ofelectric vehicle is the battery system. Vehicle autonomyand therefore accurate detection of battery state of charge areamong the main drawbacks that prevent he spread of electricvehicles in the consumer market.This paper deals with the analysis of battery state of charge:performances of B few sizes of batteries are analyzed and theirstate of charge is estimated with a Neural Network (NN) baredsystem. The obtained results have been used to design a ion.lithium battery pack suitable lor electric vehicles. The proposedSystem presents high capability of energy recovering in brakingconditions, together with charge equalization, over and undervoltage protection. Moreover a Neural Network basedestimation of battery state of charge has been implemented inorder to optimize autonomy instead of perfarmanas or viceversadepending on journey.


2003 - Feasibility, test and novel design of battery packs for EV Scooter [Relazione in Atti di Convegno]
Casasso, P.; Fratta, A.; Giraudo, G.; Guglielmi, P.; Villata, F.; Franceschini, G.
abstract

Electrical vehicles autonomy is usually affected by cells low energy density. In an EV scooter, due to the limited room and weight available, this becomes a design critical point. Li-Ion cells seem to be the best solution to set up a good autonomy vehicle with a reasonable weight and volume occupation. Two different kinds of batteries are then tested to point out the single cell actual behavior. Afterwards, charge and discharge voltage profiles are obtained for a small pack and the best performing battery type is chosen. According to the observed cell to cell voltage mismatch, a monitor and balancing circuit is designed to provide individual cell protection and maximize the final packs exploitation.


2003 - Induction motors Diagnosis using Deceleration Test, a possible Improvement [Relazione in Atti di Convegno]
Bellini, A.; Concari, C.; Franceschini, G.; Lorenzani, Emilio; Tassoni, C.; Toliyat, H. A.
abstract

Non-invasive diagnosis of incipient or actual faults ofgrid supplied induction machine is a well known technology.Motor Current Signature Analysis (MCSA) can be used forrotor and stator defects. These include stator current harmonicsat frequencies (1± 2s) f and also determining the negativesequence component of current space vector. Recently,deceleration tests which possibly can remove several drawbacksof MCSA have been proposed for rotor and stator faultdiagnosis.This paper attempts to compare the MCSA-based diagnosticprocedures with the results obtained using the deceleration tests.Experimental results show that although the deceleration testdoes not provide clear information on rotor defects, it provides adiagnostic index directly related to the percentage of shortedturns. This diagnostic index can be used to validate the MCSAbased diagnostic procedure.


2002 - On-field experience with online diagnosis of large induction motors cage failures using MCSA [Articolo su rivista]
Bellini, Alberto; Filippetti, F.; Franceschini, G.; Tassoni, C.; Passaglia, R.; Saottini, M.; Tontini, G.; Giovannini, M.; Rossi, A.
abstract

The experience gained by ENEL Produzione (previously the Italian Electric Board) on monitoring large induction motors cage condition is reported in this paper. The diagnostic procedure is based on the motor current signature analysis and, in particular, on the two sideband current components near the frequency fundamental line that appear in the current power spectrum when a rotor bar/ring breakage occurs. According to the developed procedure, a diagnostic index obtained from these components is stored and its trend as a function of time allows for the detection of the occurrence of a failure in most cases. This event is clearly shown by the overcoming of a prefixed and triggered threshold. Moreover, machines with particular rotor magnetic structure are considered. In this case, unexpectedly high sideband components appear, even in the presence of healthy cages, and the test procedure was adapted to account for these conditions.


2001 - Quantitative Evaluation of Induction Motor Broken Bars By Means of Electric Signals Signatures [Articolo su rivista]
Alberto, Bellini; Filippetti, F.; Franceschini, G.; Tassoni, C.; Kliman, G. B.
abstract

The paper reports the comparison and performance evaluation of different diagnostic procedures that use input electric signals to detect and quantify rotor breakage in induction machines supplied by the mains. Besides the traditional current signature analysis based on one-phase current spectrum lines at frequencies around the fundamental, the procedures based on analysis of the line at frequency sf in the spectrum respectively of electromagnetic torque, space vector current modulus, and instantaneous power are considered. These last procedures have similar features and the comparison is developed on the basis of instantaneous torque. It is addressed that the speed ripple introduces two further terms in the instantaneous torque, decreasing the accuracy of the diagnosis. It is shown that there is a link between the angular displacement of the current sideband components at frequencies around the fundamental. This allows a more correct quantitative evaluation of the fault and shows the superiority of the sideband current components diagnostic procedure over the other proposed methods.


2000 - Closed Loop Control Impact on the Diagnosis of Induction Motors Faults [Articolo su rivista]
Bellini, Alberto; Filippetti, F.; Franceschini, G.; Tassoni, C.
abstract

In this paper, the impact of control on faulted induction machine behavior is presented. The diagnostic indexes usually used for open-loop operation are no longer effective. Simulation and experimental results show that the spectrum of the field current component in a field-oriented controlled machine has suitable features that can lead to an effective diagnostic procedure. Specifically, in the case of stator and rotor faults the spectrum components at frequencies 2sf and -2sf, respectively, are quite independent of control parameters and dependent on the fault extent.


2000 - Impact of cross saturation in synchronous reluctance motors of the transverse-laminated type [Articolo su rivista]
Vagati, A.; Pastorelli, M.; Scapino, F.; Franceschini, Giovanni
abstract

The cross-saturation phenomenon in synchronous reluctance motors is extensively analyzed, with a main reference to motors of the transverse-laminated type. A mixed theoretical and experimental approach is adopted, aiming at definition of the motor's behavior when large overload currents are driven up to ten times the rated current. As a consequence, a special test and measuring procedure has been adopted. The obtained results are used to check the validity of the adopted model and to prove the unexpected overload performance of this motor.


2000 - Monitoring of induction motor load by neural network techniques [Articolo su rivista]
Salles, Gael; Filippetti, Fiorenzo; Tassoni, Carla; Grellet, Guy; Franceschini, Giovanni
abstract

This paper deals with the electric tracing of the load variation of an induction machine supplied by the mains. A load trouble, like a torque dip, affects the machine supply current and consequently it should be possible to use the current pattern to detect features of the torque pattern, using the machine itself as a torque sensor. But current signature depends on many phenomena and misunderstandings are possible. At first the effect of different load anomalies on current spectrum, in comparison with other machine troubles like rotor asymmetries, are investigated. Reference is made to low frequency torque disturbances, which cause a quasistationary machine behavior. Simplified relationships, validated by simulation results and by experimental results, are developed to address the current spectrum features. In order to detect on-lines anomalies, a current signature extraction is performed by the time-frequency spectrum approach. This method allows the detection of random fault as well. Finally it is shown that a Neural Network approach can help the torque pattern recognition, improving the interpretation of machine anomalies effects.


2000 - Recent developments of induction motor drives fault diagnosis using AI techniques [Articolo su rivista]
Filippetti, Fiorenzo; Franceschini, Giovanni; Tassoni, Caria; Vas, Peter
abstract

This paper presents a review of the most recent developments in the field of diagnosis of electrical machines and drives based on artificial intelligence (AI). It covers the application of expert systems, artificial neural networks (ANNs), and fuzzy logic systems that can be integrated into each other and also with more traditional techniques. The application of genetic algorithms is considered as well. In general, a diagnostic procedure starts from a fault tree developed on the basis of the physical behavior of the electrical system under consideration. In this phase, the knowledge of well-tested models able to simulate the electrical machine in different fault conditions is fundamental to obtain the patterns characterizing the faults. The fault tree navigation performed by an expert system inference engine leads to the choice of suitable diagnostic indexes, referred to a particular fault, and relevant to build an input data set for specific AI (NNs, fuzzy logic, or neuro-fuzzy) systems. The discussed methodologies, that play a general role in the diagnostic field, are applied to an induction machine, utilizing as input signals the instantaneous voltages and currents. In addition, the supply converter is also considered to incorporate in the diagnostic procedure the most typical failures of power electronic components. A brief description of the various AI techniques is also given; this highlights the advantages and the limitations of using AI techniques. Some applications examples are also discussed and areas for future research are also indicated.


1999 - Closed loop control impact on the diagnosis of induction motors faults [Relazione in Atti di Convegno]
Bellini, A.; Filippetti, F.; Franceschini, G.; Tassoni, C.
abstract

In this paper the impact of control on faulted induction machine behavior is presented. The diagnostic indexes usually used for open-loop operation are no more effective. Simulation and experimental results show that the spectrum of the field current component id in a field-oriented controlled machine has suitable features that can lead to an effective diagnostic procedure for closed loop induction machines. Specifically in case of stator and rotor faults the spectrum components at frequencies respectively -f and 2sf are quite independent of control parameters and dependent on the fault extent.


1999 - Flux-observer-based high-performance control of synchronous reluctance motors by including cross saturation [Articolo su rivista]
Vagati, Alfredo; Pastorelli, Michele; Franceschini, Giovanni; Drogoreanu, Valentin
abstract

A fully digital control scheme is presented, based on a particular type of flux observer. This includes a quite accurate magnetic model of the motor, taking into account cross saturation. This model is first described and, then, the practically obtained control performance is shown, giving evidence to the impact of such a model on the system behavior.


1998 - AI techniques in induction machines diagnosis including the speed ripple effect [Articolo su rivista]
Filippetti, Fiorenzo; Franceschini, Giovanni; Tassoni, Caria; Vas, Peter
abstract

Various applications of artificial intelligence (AI) techniques (expert systems, neural networks, and fuzzy logic) presented in the literature prove that such technologies are well suited to cope with on-line diagnostic tasks for induction machines. The features of these techniques and the improvements that they introduce in the diagnostic process are recalled, showing that, in order to obtain indication on the fault extent, faulty machine models are still essential. Moreover, by the models, that must trade off between simulation result effectiveness and simplicity, it is possible to overcome crucial points of the diagnosis. With reference to rotor electrical faults of induction machines, a new and simple procedure based on a model which includes the speed ripple effect is developed. This procedure leads to a new diagnostic index, independent of the machine operating condition and inertia value, that allows the implementation of the diagnostic system with a minimum configuration intelligence. -. © 1998 IEEE.


1998 - Cross-saturation in Synchronous Reluctance motors of the transverse-laminated type [Relazione in Atti di Convegno]
Vagati, A.; Pastorelli, M.; Scapino, F.; Franceschini, G.
abstract

The cross-saturation phenomenon in Synchronous Reluctance motor is extensively analyzed, with a main reference to motors of the transverse-laminated type. A mixed, theoretical and experimental approach is adopted, aiming at definition of motor's behavior when large overload currents are driven, up to ten times the rated current. As a consequence, a special test and measuring procedure has been adopted. The obtained results are used to check the validity of the adopted model and to prove the unexpected overload performance of this motor. Finally, the tendential behavior at infinite current is discussed.


1998 - Design of low-torque-ripple synchronous reluctance motors [Articolo su rivista]
Vagati, Alfredo; Pastorelli, Michele; Franceschini, Giovanni; Petrache, S. C.
abstract

A design approach oriented to minimization of torque ripple is presented for synchronous reluctance motors of the transverse-laminated type. First, the possible types of rotors are classified and the more suited rotor structure is evidenced, to be matched to a given stator. Then, the inner rotor design is described, pointing out the low-ripple measures. Last, experimental results are given from three different rotors; they confirm the validity of the proposed approach. © 1998 IEEE.


1998 - Monitoring of induction machines load torque disturbances: An alternative NN-based method [Relazione in Atti di Convegno]
Filippetti, F.; Grellet, G.; Salles, G.; Franceschini, G.; Tassoni, C.
abstract

This paper addresses the problem of the real time rebuilding of the load torque disturbances in asynchronous machines. Since the load pattern modifies the motor's supply current, it should be possible to use the current pattern to rebuild torque pattern, utilizing the machine itself as a torque sensor. In the paper the problem is studied utilizing both relationships developed under simplifying assumptions and a more complex model of the machine. The results obtained are compared with the experimental ones. Reference is made to low frequency torque disturbances, that cause a quasi-stationary machine behavior. It is shown that a Neural Network approach can be an alternative and efficient method for the torque pattern recognition.


1998 - Position sensorless control of a SRM drive using ANN-techniques [Relazione in Atti di Convegno]
Bellini, A.; Filippetti, F.; Franceschini, G.; Tassoni, C.; Vas, P.
abstract

Nowadays speed-sensorless electromechanical drives are feasible for many applications. The elimination of the mechanical transducer increases reliability, reducing costs. As far as synchronous machine drives are concerned this issue is critical since the rotor position is fundamental to derive the proper switching sequence. If a SRM is used as actuator, different sensorless techniques have been proposed, essentially based on the rotor position detection by reluctance variation. Being the SRM a highly non-linear machine, it is an ideal candidate for the application of Artificial Neural Networks (ANNs). In this paper, at first the results of a mixed closed loop scheme for the sensorless identification of a SRM drive are presented. A radial basis function ANN has been used, since it is well suited to simulate a non-linear system in a wide operating area. Then the proposed ANN is applied within a standard control scheme as a position sensor. Simulation results show the effectiveness of the proposed method, since a good agreement is reached with experimental results obtained from a SRM drive with a standard position sensor.


1998 - Recent developments of induction motor drives fault diagnosis using AI techniques [Relazione in Atti di Convegno]
Filippetti, Fiorenzo; Franceschini, Giovanni; Tassoni, Carla; Vas, P.
abstract

The paper presents a review of the recent developments in the field of diagnosis of electrical machines and drives based on artificial intelligence (AI). This review covers the application of expert systems, neural networks and fuzzy logic systems that can be integrated into each other and also with more traditional techniques to overcome specific problems. Usually a diagnostic procedure starts from a fault tree developed on the basis of the physical behaviour of the electrical system under consideration. In this phase the knowledge of well tested models able to simulate the electrical machine in different fault conditions is fundamental to obtain the patterns characterizing the faults. Then the fault tree navigation performed by an expert system inference engine leads to the choice of suitable diagnostic indexes, referred to a particular fault, and relevant to build an input dataset for specific AI (neural networks, fuzzy logic or neuro-fuzzy) systems. The discussed methodologies, that play a general role in the diagnostic field, are applied to an induction machine, utilizing as input signals the instantaneous voltages and currents. In addition, the supply converter is also considered to also incorporate in the diagnostic procedure the most typical failures of power electronic components. A brief description of the various techniques is provided, to highlight the advantages and the validity limits of using AI technologies. Some application examples are discussed and, areas for future research are also indicated.


1997 - Design of low-torque-ripple synchronous reluctance motors [Relazione in Atti di Convegno]
Vagati, A.; Pastorelli, M.; Franceschini, G.; Petrache, C.
abstract

A design approach oriented to minimization of torque-ripple is presented, for synchronous reluctance motors of the transverse-laminated type. First, the possible types of rotors are classified and the more suited rotor structure is evidenced, to be matched to a given stator. Then, the inner rotor design is described, pointing-out the low-ripple measures. Last, experimental results are given, from three different rotors: they confirm the validity of the proposed approach.


1997 - Digital observer-based control of synchronous reluctance motors [Relazione in Atti di Convegno]
Vagati, A.; Pastorelli, M.; Franceschini, G.; Drogoreanu, V.
abstract

A fully-digital control scheme is presented, based on a particular type of flux-observer. This includes a quite accurate magnetic model of the motor, taking into account cross-saturation. The model is firstly described. Then, the practically obtained control performance are shown, giving evidence to the impact of such a model.


1997 - High-performance control of synchronous reluctance motors [Articolo su rivista]
Vagati, Alfredo; Pastorelli, Michele; Franceschini, Giovanni
abstract

Based on a (d, q) synchronous frame, the control problems of synchronous reluctance motors are outlined. In particular, the effect of magnetic saturation, core loss, and angular measurement errors of various types are evidenced. A flux-observer-based control scheme, capable of overcoming most of the above problems, is proposed. The proposed control has been implemented on a prototype drive, adopting a 17-N-m 8000-r/min motor. The experimental results show quite a good performance, with particular emphasis on those applications which require a large constant-power speed range. © 1997 IEEE.


1997 - Thermal characterisation of IGBT power modules [Articolo su rivista]
Cova, P.; Ciappa, M.; Franceschini, G.; Malberti, P.; Fantini, Fausto
abstract

In this paper we report on experimental techniques for the thermal characterization of IGBT power modules.


1996 - AC motors for high-performance drives: A design-based comparison [Articolo su rivista]
Vagati, Alfredo; Fratta, Antonino; Franceschini, Giovanni; Rosso, Piermario
abstract

Three ac motors are compared for application in high-performance controlled drives: induction, brushless, and synchronous reluctance motors. Their design is optimized under common design assumptions. Then, the given stall-torques are compared to each other. In addition, the quadrature reactances are compared, as affecting overload and flux-weakening performances. Last, applicative considerations are given, thus defining the most suitable solution for each field. © 1996 IEEE.


1996 - AI techniques in induction machines diagnosis including the speed ripple effect [Relazione in Atti di Convegno]
Filippetti, F.; Franceschini, G.; Tassoni, C.; Vas, P.
abstract

Various applications of AI techniques (expert systems, neural networks and fuzzy logic) presented in the literature prove that such technologies are well suited to cope with on-line diagnostics tasks for induction machines. The features of these techniques and the improvements that they introduce in the diagnostic process are recalled, showing that, in order to obtain indication on the fault extent, faulty machine models are still essential. The models must trade off between simulation result effectiveness and simplicity. With reference to rotor electrical faults of induction machines, a new and simple model which includes the speed ripple effect is developed. This model leads to a new diagnostic index, independent of the machine operating condition and inertia value, that allows the implementation of the diagnostic system with a minimum configuration intelligence.


1996 - Fault operations of inverter-fed induction motor [Relazione in Atti di Convegno]
Gentile, G.; Rotondale, N.; Tursini, M.; Franceschini, G.; Tassoni, C.
abstract

This paper presents an investigation of the fault mode operations of a largely diffused class of electric drives, the inverter-fed induction motor drives. The attention is focused on some usual non catastrophic faults, i.e. those faults that don't cause the current and voltage exceed the safe limit. The investigation is carried out by monitoring only the input/output variables of each sub-system that composes the drive. The behaviour of typical faults such as the open phase at motor terminal, the base drive loosening of an inverter switch and the fault of the filter capacitance are presented and discussed. Simulations and spectrum analyses followed by experimental validations are shown.


1996 - High performance control of synchronous reluctance motor [Relazione in Atti di Convegno]
Vagati, A.; Pastorelli, M.; Franceschini, G.
abstract

Based on (d, q) synchronous frame, the control problems of synchronous reluctance motors are outlined. In particular, the effect of magnetic saturation, core loss and angular measurement errors of various type are evidenced. A flux-observer based control scheme is proposed, capable of overcoming most of the above problems. The proposed control has been implemented on a prototype drive, adopting a 17 Nm, 8,000 rpm motor. The experimental results show a quite good performance, with particular emphasis to those applications which require a large constant-power speed range.


1996 - Induction machine stator fault on-line diagnosis based on LabVIEW environment [Relazione in Atti di Convegno]
Collamati, L.; Filippetti, F.; Franceschini, G.; Pirani, S.; Tassoni, C.
abstract

The benefits of machine condition monitoring have been widely recognized as superior with respect to other alternative maintenance approaches. As matter of fact, condition monitoring is an operational strategy for machine integrity assessment, fault identification and life extension. The cost-benefit ratio will be reduced in progress owing to the commercial diagnostic environment availability. This paper presents the implementation of a diagnostic procedure to detect induction machine stator faults based on LabVIEW environment. The diagnosis is performed by using a suitable neural network, trained by faulted machine simulator, that has, as input variables, the negative sequence current component and the variation of the positive sequence current component between actual and healthy machine conditions. The statement of a trigger threshold that discerns between true faults and intrinsic disymmetry of the machine is discussed as well.


1996 - Neural network architectures for fault diagnosis and parameter recognition in induction machines [Relazione in Atti di Convegno]
Filippetti, F.; Uncini, A.; Piazza, C.; Campolucci, P.; Tassoni, C.; Franceschini, G.
abstract

This paper presents a neural network that is able to give, together with the rotor fault diagnosis, the combined rotor-load inertia momentum of an induction machine. The inputs of the network are the spectral components of machine input currents, speed and torque. A specific neural network architecture containing new fast spline-based neurons with improved generalization capabilities has been used. The training set is obtained by a faulted machine dynamical model as simulator.


1996 - Survey of neural network approach for induction machine on-line diagnosis [Relazione in Atti di Convegno]
Filippetti, F.; Franceschini, G.; Ometto, A.; Meo, S.
abstract

Fault detection and diagnosis is currently a very important problem in induction machine management. Both model-based method and expert systems have been suggested to solve the problem. Recently neural networks have been advocated as a possible technique to handle diagnostic tasks providing them with an effective improvement. Neural networks can be applied autonomously or can integrate with existing diagnostic tools. Several architectures for fault diagnosis are studied. In this paper the attention is focused to the multilayer perceptron and to the self organizing map networks which, with different features, seem best suited for induction machine diagnostic tasks. The application of the different neural architectures to specific problem by practical examples is discussed. In particular it will be shown that the synergy between the two mentioned neural architectures provides a global diagnosis approach: NNs specifically trained for dealing with certain tasks are the basic elements. A first level NN classifies the fault, then several second level fault specific NNs (FS-NNs) for stator short-circuits, bearing damages, rotor bar breakages etc. evaluate the fault severity.


1995 - A.C. motors for high-performance drives: a design-based comparison [Relazione in Atti di Convegno]
Vagati, A.; Fratta, A.; Franceschini, G.; Rosso, P. M.
abstract

Three a.c. motors are compared, for application in high-performance controlled drives: induction, brushless and synchronous reluctance motors. Their design is optimized, under common design assumptions. Then, the given stall-torques are compared to each other. In addition, the quadrature reactances are compared, as affecting overload and flux-weakening performances. Last, applicative considerations are given, thus defining the most suitable solution for each field.


1995 - LabVIEW based virtual instrument for on-line induction motor parameters identification [Relazione in Atti di Convegno]
Filippetti, F.; Pirani, S.; Tommasini, L.; Franceschini, G.
abstract

An automatic procedure to identify on-line the induction machine parameters of the steady-state equivalent circuit is presented. The procedure starts with the acquisition of input current and voltage instantaneous values and their process to obtain the following dataset of variables: current and voltage first harmonic values, their displacement and the slip value. The slip value is obtained through the current spectrum lines due to the rotor slotting. This first step is automatically iterated if the operating condition changes, to obtain more sets of variables. Different methods identify the parameters of the equivalent circuit, starting from the available sets of variables. All the process, configured as a virtual instrument, is implemented in LabVIEW environment and can be included in a diagnostic system to detect machine healthy conditions, in order to expand system capabilities.


1995 - Neural network aided on-line diagnostics of induction machine stator faults [Relazione in Atti di Convegno]
Filippetti, F.; Franceschini, G.; Tassoni, C.; Meo, S.; Ometto, A.
abstract

A Multy Layer Perceptron Neural Network able to recognize inter-turn short-circuits in the stator of induction machines is presented. The network is inserted in an on-line diagnostic system which utilizes the machine voltages and currents as input signals. The current computed by a faulted machine models are analyzed with the aim to evidence the variables more suitable to characterize the short circuit's effects. These variables, properly normalized, are the input data sets for the learning process of the network, which is therefore applicable to a class of induction machines.


1995 - Neural networks aided on-line diagnostics of induction motor rotor faults [Articolo su rivista]
Filippetti, Fiorenzo; Franceschini, Giovanni; Tassoni, Carla
abstract

An improvement of induction machine rotor fault diagnosis based on a neural network approach is presented. A neural network can substitute in a more effective way the faulted machine models used to formalize the knowledge base of the diagnostic system when inputs and outputs are suitably chosen. Training the neural network by data achieved through experimental tests on healthy machines and through simulation in case of faulted machines, the diagnostic system can discern between 'healthy' and 'faulty' machines. This procedure substitutes the statement of a trigger threshold, required by the diagnostic procedure based on the machine models.


1994 - A genetic algorithm approach to design flux observer for induction servo motors [Relazione in Atti di Convegno]
Franceschini, G.; Piazzi, A.; Tassoni, C.
abstract

In this paper we present a new approach to the design of robust flux observer for induction servo motors. The novelty lies in adopting a genetic algorithms to synthesise a flux observer which is robust against very large perturbations of machine model parameters and different operational conditions. By means of a suitable object function associated to any flux observer it is possible to compare the performances of a population of observers. The genetic algorithm, by means of the mechanism of natural selection and natural genetics drives the evolution of the observer population until an optimal robust flux observer is emerged.


1994 - A simple current regulator for flux-weakened operation of high performance synchronous reluctance drives [Relazione in Atti di Convegno]
Fratta, Antonino; Petrache, Cornel; Franceschini, Giovanni; Troglia, GianPiero
abstract

High anisotropy synchronous reluctance machines are becoming a practical and cheap choice for high performance drives, but simple control solutions are still investigated because of control sensitivity to anisotropy ratio. Torque sensitivity is discussed with respect to model errors due to iron loss and saturation. A control strategy is derived, based on simple three-phase current regulation with feed-forward emf compensation. The lack of control at voltage saturation, usually related to this choice, is reinvestigated by means of stability analysis, defining the inverter's model up to six-step operation. A novel voltage phase-leading method is then proposed and analysed. Analytical design relationships are derived and implemented in a prototype drive adopting a high anisotropy motor. Experimental results verify analytically predicted flux-weakened performances, up to quasi-six-step operation. Interesting drive behaviour is also shown in the constant-torque speed range.


1994 - Broken bar detection in induction machines: comparison between current spectrum approach and parameter estimation approach [Relazione in Atti di Convegno]
Filippetti, F.; Franceschini, G.; Tassoni, C.; Vas, P.
abstract

The diagnosis of induction machine rotor electrical faults is studied by comparing the (a) current spectrum analysis and the (b) apparent rotor resistance estimation. The first approach is used to develop several procedures based on fault models of the machine. The experience gained in the development of such procedures is used to approach the estimation method from a theoretical point of view. Using a simplified model of faulted machine, a relationship that correlates the apparent resistance variation with the number of broken bars is obtained. By this relationship it is possible to have indication on the sensitivity of the parameter estimation approach. The superiority of the current spectrum approach over the parameter estimation approach is shown.


1993 - Neural networks aided on-line diagnostics of induction motor rotor faults [Relazione in Atti di Convegno]
Filippetti, F.; Franceschini, G.; Tassoni Carla, Null
abstract

An improvement of induction machine rotor fault diagnosis based on neural network approach is presented. A neural network can substitute in a more effective way the faulted machine models used to formalize the knowledge base of the diagnostic system with suitably chosen inputs and outputs. Training the neural network by data achieved through experimental tests on healthy machines and through simulation in case of faulted machines, the diagnostic system can discern between `healthy' and `faulty' machines. This procedure substitutes the statement of a trigger threshold, needed in the diagnostic procedure based on the machine models.


1992 - Design criteria of high performance synchronous reluctance motors [Relazione in Atti di Convegno]
Vagati, A.; Franceschini, G.; Marongiu, I.; Troglia, G. P.
abstract

A general design approach is presented, for synchronous reluctance servomotors. The choice of the rotor's structure is extensively discussed and the most suitable solution is analyzed in detail. Optimization algorithms are given, regarding minimization of the q-axis flux and maximization of torque, at given outside diameter and power dissipation capability. Expected results are discussed and compared with the state-of-the-art.


1992 - Development of expert system knowledge base to on-line diagnosis of rotor electrical faults of induction motors [Relazione in Atti di Convegno]
Filippetti, F.; Martelli, M.; Franceschini, G.; Tassoni, C.
abstract

The paper concerns the development of the Knowledge Base branch related to rotor electrical faults in squirrel cage machines, to be implemented in an Expert System, utilizing current instantaneous values as input data. The Knowledge Base is organized in two levels: in the first level diagnostic indexes for the orientation of the E.S. inferential engine toward the appropriate branch of the fault tree are utilized. The second level includes the deep knowledge with a data set obtained on the basis of a complete faulty machine model. The diagnostic indexes of the first level concern how to distinguish 'faulty' events from the 'healthy' signals due to the unavoidable manufacturing asymmetries. They are pointed out through a simplified model of faulted rotor that needs few machine parameters. This diagnosis may substitute the second level diagnosis if the machine design data, necessary for the second level diagnosis, are not available or if the extensive work needed for the data base construction would be avoided. Some diagnosis examples are reported to describe the sequence of operations of the diagnostic system.


1991 - Current controller in synchronous reference frame for high performance AC drives [Relazione in Atti di Convegno]
Profumo, F.; Bilewski, M.; Pastorelli, M.; Boglietti, A.; Franceschini, G.
abstract

Current controlled high performance ac drives (for spindles application for example) require quick current response in transient state and low harmonic current content in steady state. In addition the transition between PWM and square wave operation has to be soft and not to cause undesirable currents and torque transients. Thus, the classical stationary reference frame P-I current regulator operates in speed and torque reduced range over which the current can be regulated instantaneously and, as a consequence, the inverter has to be derated. The authors propose a new current regulator in synchronous reference frame based on the space vector PWM modulation. The voltage reference is get through the regulation of the fundamental harmonic of the torque and flux current components in synchronous reference frame, up to when the machine back emf can be overcome. In square wave operation the drive outer control loops (speed and flux) are still active, but only the feedforward voltage control is applied. Complete simulation results are carried out in order to evaluate the validity of the proposed method in the whole speed range of operation.


1991 - Spice-Assisted Simulation of Controlled Electric Drives: An Application to Switched Reluctance Drives [Articolo su rivista]
Franceschini, Giovanni; Pirani, Stefano; Rinaldi, Mario; Tassoni, Carla
abstract

This paper describes an example of simulation of a closed-loop controled electric drive that shows the feasibility to simulate the equipment by means of a “general purpose” electronic circuit analysis program.The SPICE program is used because of its welLKnown facility to simulate electronic circuits. This paper reports a way to extend the SPICE facilities to simulate the electromechanical energy conversion and the drive control. The simulation of a switched reluctance (SR) drive with a closed-loop speed control is considered, and the results are validated by experimental tests executed on an industrial drive. © 1991 IEEE


1990 - About the gain choice of flux observer in induction servo-motors [Relazione in Atti di Convegno]
Franceschini, G.; Pastorelli, M.; Profumo, F.; Tassoni, C.; Vagati, A.
abstract

A reduced-order observer is considered for the estimation of the rotor flux in field oriented controlled servo motors. The influence of the observer gain choice on the system performance is analyzed in detail. Sensitivity to thermal variations is taken into account, as well as the influence of the error dynamics. Experimental results are given for a real drive, showing the effects of the different proposed gain choices on the drive behavior.


1989 - SPICE aided analysis of UPS vector control [Relazione in Atti di Convegno]
Delfiore, S.; Franceschini, G.; Tassoni, C.
abstract

The possibility is studied of UPS (uninterruptible power supply) control based on the voltage vector referred to a rotating reference frame with velocity corresponding to voltage pulsation and on voltage pulsation itself. To verify the feasibility of the control strategy, a SPICE-aided simulation is reported. The numerical results show that, with asymmetrical load, a pulsation ripple is present owing to the nonsinusoidal voltage waveforms. Nevertheless, the computer harmonic distortion values are acceptable.


1989 - SPICE assisted simulation of controlled electric drives: An application to switched reluctance drives [Relazione in Atti di Convegno]
Franceschini, G.; Pirani, S.; Rinaldi, M.; Tassoni, C.
abstract

An example of the simulation of a closed loop controlled electric drive that shows the feasibility of simulating this equipment by means of a general-purpose electronic circuit analysis program is described. A SPICE program is used owing to its well-known facility for simulating electronic circuits. Its application to the control of a switched reluctance drive is presented. A way to extend SPICE to the simulation of the electromechanical energy conversion and the drive control is also presented. A closed-loop speed control is considered, and the simulation results are validated by experimental tests executed on an industrial drive.