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EMILIO LORENZANI

Professore Ordinario
Dipartimento di Scienze e Metodi dell'Ingegneria


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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.


- 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.


2022 - Optimized Parallel Hybrid Amplifier for Print-Head Piezoelectric Actuators with Trapezoidal Waveforms [Articolo su rivista]
Migliazza, G.; Carfagna, E.; Bernardi, F.; Lorenzani, E.
abstract

Most of the drivers used to control high-frequency print-head piezoelectric actuators are based on linear technology (e.g., Class AB amplifiers) which dissipate a large amount of power for this specific application. This choice is given by the necessary of very precise tracking and large bandwidth for the closed-loop voltage control of the piezoelectric load. This work highlights the critical issues of pure Class D amplifiers and hybrid (switching and linear) solutions. Then a new hybrid power amplifier topology is proposed analyzing its advantages and drawbacks for these kind of piezoelectric loads reducing energy consumption. First of all, the performance of the proposed solution is verified by simulations in LTspice environment. Experimental results showed the effectiveness of the proposed solution potentially paving the way to a larger adoption of this topology for high-frequency piezoelectric actuators. The proposed solution is patent pending.


2022 - Output Voltage Overshoot Suppression Control for Multilevel Inverter Architectures [Relazione in Atti di Convegno]
Bernardi, Fabio; Lorenzani, Emilio; Savi, Filippo; Nuzzo, Stefano; Barater, Davide
abstract


2022 - Performance Analysis of Current Control Strategies for Hybrid Stepper Motors [Articolo su rivista]
Bernardi, F; Carfagna, E; Migliazza, G; Buticchi, G; Immovilli, F; Lorenzani, E
abstract

Hybrid stepper motors are widespread in industrial automation due to their robustness and high torque performance in low speed range, e.g. 3D printers, pick and place, and generally in many low power positioning applications. In order to increase the efficiency and dynamic performance, current/speed/position closed loop controls are implemented for high performance sensored stepper drives. The main challenge comes from the high number of magnetic poles which these motors feature, increasing the ratio between the fundamental and switching frequency. This paper critically evaluates four current control structures based field oriented control: classic PI regulators, sliding mode control, deadbeat predictive current control and model predictive current control. Simulations and experimental results aim to evaluate the dynamic performance, phase current amplitude and distortion in order to support the critical comparison.


2022 - Reconfigurable Multi-Three-Phase Drive for Naval Rim-Driven Propulsion System [Articolo su rivista]
Alosa, C.; Migliazza, G.; Immovilli, F.; Lorenzani, E.
abstract

Multiphase drives are the subject of great interest for the transportation electrification. Multi-three-phase machines are used with modular three-phase converters to obtain a redundant structure and their great advantage is the fault-tolerance capability. Starting from a symmetrical multi-three-phase machine, a reconfigurable architecture drive can be obtained. The main characteristic of a reconfigurable architecture is the ability to change the winding configuration to better match the operating point, specifically the machine speed. The main advantage of this architecture is the capability of reducing the number of active converters when the machine operates at low speed, thus reducing total converter power losses. However, system complexity increases, since reconfiguration cells are needed to interconnect the winding sets. The proposed reconfigurable multi-three-phase drive architecture exhibits two main benefits at low speed operation: increased efficiency and reduced phase current ripple for a given switching frequency. The reconfigurable architecture was assessed by means of analytical as well as numerical simulations, and the benefits obtainable at low speed operation were also demonstrated experimentally on a reduced scale prototype, capable of 'on the fly' reconfiguration without stopping the machine.


2021 - Assessment of a Multi-Functional Converter System for Traction Electric Drives [Relazione in Atti di Convegno]
Alosa, C.; Immovilli, F.; Lorenzani, E.
abstract

The introduction of strict regulations in terms of air pollution is pushing automotive industry and heavy equipments vehicles manufacturers to integrate electric drives into the powertrain. To overcome the limitations on maximum battery voltage, a DC-DC bidirectional boost converter stage between the battery and the inverter is widely adopted by manufacturers. However, these converters are bulky, expensive and impact on the system efficiency. For this reason, Multi-Functional Converter Systems (MFCS) have been introduced in order to avoid the voltage boost stage and take advantage of the electric motor and the inverter to integrate the boost converter within these two components. This paper carries out a comparison between a traditional architecture, with a DC-DC boost converter stage, and a MFCS, to determine the best solution in terms of efficiency, weight and encumbrance.


2021 - Assessment of master-slave and droop control strategies in multi-three-phase drives [Relazione in Atti di Convegno]
Benatti, D.; Alosa, C.; Carfagna, E.; Immovilli, F.; Lorenzani, E.
abstract

Multi-phase electric drives can be employed in a great variety of applications. Their advantage in terms of fault-tolerance capability is becoming the focus of the work of many research activities, especially in the field of transportation electrification. The main topic is to create redundant and modular multi-three-phase drives to increase the overall system reliability and fault-tolerance. To this aim, distributed control architectures have been assessed. In this paper, a centralized master-slave control is compared against a distributed droop control architecture, in order to identify advantages and drawbacks. Both of the control strategies are applied to a double three-phase drive. The aim of the work is to assess whether the droop control architecture can be a valid alternative to a centralized master-slave control in terms of performances, but with the additional benefit of having a proper full redundant fault-tolerant application.


2021 - DC Current Control for a Single-Stage Current Source Inverter in Motor Drive Application [Articolo su rivista]
Migliazza, G.; Buticchi, G.; Carfagna, E.; Lorenzani, E.; Madonna, V.; Giangrande, P.; Galea, M.
abstract

The current source inverter (CSI) is a power electronics topology that allows for the realization of variable speed drives (VSD). Compared to the most common voltage source inverter (VSI), which can be directly connected to a voltage source, the CSI needs a prestage to generate a constant current bus. This article therefore seeks to challenge this 'accepted' consideration that a CSI always needs this precircuit and seeks to remove this circuit by proposing an innovative $i_{dc}$ current control scheme. The proposed scheme is applied to a single stage motor drive driven by a CSI converter. It is shown how implementing this control scheme removes the need for the front-end stage, thus removing an unnecessary converter and optimizing the efficiency at the same time. The CSI state-space equations are presented and the developed models are verified using simulations. Stability analysis of small-signal model is considered through Nyquist criterion with the robustness in presence of variations of the most important system parameters. Experimental results driving a permanent magnet synchronous machine (PMSM) are shown confirming the validity of the proposed control, potentially paving the way to a larger adoption of the CSI topologies for motor drive applications.


2021 - Effect of semiconductor parasitic capacitances on ground leakage current in three-phase current source inverters [Articolo su rivista]
Migliazza, G.; Carfagna, E.; Buticchi, G.; Immovilli, F.; Lorenzani, E.
abstract

This paper investigates the influence of power semiconductor parasitic components on the ground leakage current in the three-phase Current Source Inverter topology, in the literature called H7 or CSI7. This topology allows reducing converter conduction losses with respect to the classic CSI, but at the same time makes the topology more susceptible to the parasitic capacitances of the semiconductors devices. In the present work, a grid-connected converter for photovoltaic power systems is considered as a case study, to investigate the equivalent circuit for ground leakage current. The same analysis can be extended to applications regarding electric drives, since the HF model of electric machines is characterized by stray capacitance between windings and the stator slots/motor frame. Simulation results proved the correctness of the proposed simplified common-mode circuit and highlighted the need of an additional common-mode inductor filter in case of resonance frequencies of the common-mode circuit close to harmonics of the power converter switching frequency. Experimental results are in agreement with the theoretical analysis.


2021 - Extended Speed Range Control for a Current Source Inverter Variable Speed Drive [Relazione in Atti di Convegno]
Migliazza, G.; Carfagna, E.; Buticchi, G.; Immovilli, F.; Lorenzani, E.
abstract

Voltage Source Inverters (VSIs) are usually adopted for high-speed motor drive applications due to the topology simplicity and the wide availability of control strategies for this topology. An alternative is the Current Source Inverter (CSI) which allows to achieve high speed range with limited DC voltage due to its intrinsic boost capability, and this is of interest in aerospace applications or electrical vehicles (EV), but a pre-stage is necessary to control the DC input current. In this work an hybrid solution is proposed to extend the speed range of a single stage CSI (i.e. CSI without pre-stage) driving a Permanent Magnet Synchronous Machine (PMSM). In fact using a single stage CSI with DC current control, the machine cannot work properly in low speed region, so the control is composed by two different strategies: one is proposed in this work for low speed operations and the other one is already known for high speed.


2021 - Iron Losses Impact on High-Speed Drives [Relazione in Atti di Convegno]
Carfagna, E.; Lorenzani, E.; Debbadi, K.; Pugliese, S.; Liserre, M.
abstract

Higher magnitudes of the stator currents, low efficiency, and degradation of the output torque in high speed machine are caused by iron losses, which are not sufficiently small to be neglected. A Finite Control Set Model Predictive Control (FCS-MPC) which takes iron losses into account in the prediction model on a high speed motor is proposed in this paper and compared to classical FCS-MPC that neglects iron losses influence. Performances of both models are analysed and compared under steady-state and transient conditions including acceleration condition using a 3-Level Hybrid Active Neutral Point Clamped (HANPC) inverter topology. Accurate simulations of a 3-Level HANPC inverter driving a high speed PMSM are presented comparing the proposed control respect to classical FCS-MPC and the classical Field Oriented Control (FOC) together with neutral point (NP) balance and loss minimization control (LMC).


2021 - PLL-Based Sensorless Control for Single-Stage Current Source Inverter in Motor Drive Application [Relazione in Atti di Convegno]
Carfagna, E.; Migliazza, G.; Buticchi, G.; Lorenzani, E.; Xu, Z.; Zou, Z.; Zhang, H.
abstract

The Current Source Inverters (CSIs) are an alternative to Voltage Source Inverters (VSIs) for electric motor applications. Despite the advantageous characteristics of intrinsic voltage boost capability, absence of electrolytic capacitors and reduced machine voltage stress, the increased component count and the need of a pre-stage for the inductor current control have limited the adoption. For some applications which have to operate always above a base speed (e.g. pumps, actuators, fans), single-stage CSI converter with improved efficiencies have been proposed. Owing to the advantage of the direct measurement of the terminal voltage, a simple and robust sensorless control is proposed for a single-stage CSI converter. Simulations on a SiC-based CSI7 converter driving a Permanent Magnet Synchronous Machine (PMSM) confirm the validity of the proposed control, potentially paving the way to a larger adoption of the CSI7 topology for motor drive application.


2020 - Fault-Tolerant Multi-Three-Phase PMSM Machine for Offroad Vehicle Hybridization [Relazione in Atti di Convegno]
Alosa, C.; Immovilli, F.; Lorenzani, E.
abstract


2020 - Ground Leakage Current in Three-Phase Current Source Inverters Depending on Power Semiconductors Parasitic Capacitances [Relazione in Atti di Convegno]
Migliazza, G.; Carfagna, E.; Bernardi, F.; Lorenzani, E.
abstract

This paper analyzes the relation between the ground leakage current and the power semiconductor parasitic components of a three-phase Current Source Inverter (CSI) topology named in literature H7 or CSI7. This topology is characterized by the presence of an additional switch which allows to reduce conduction power losses and decouple the DC side from the AC side during the application of the Zero current Vector to reduce ground leakage current. This work deals with the significant variation of this current depending on power converter parasitic capacitors. In this work the analysis is applied to grid-connected converters for a string photovoltaic applications, even if the behavior is the same also in case of electrical drives. The analysis is assessed by numerical simulations and experimental results with different parasitic capacitances that confirm also the validity of the proposed equivalent common-mode circuit.


2020 - Multi-three-phase propulsion system for fault-tolerant naval rim-driven propeller [Relazione in Atti di Convegno]
Alosa, C.; Immovilli, F.; Lorenzani, E.
abstract

Multi-phase machines are gaining popularity especially in the field of transportation electrification. Multi-three-phase machines used in conjunction with modular three-phase converters result in a redundant structure with the great advantage of fault-tolerance operation capability. The present work reports the study of a multi-three-phase machine for a rim-driven propeller pod, to be employed in yachting boat electrification. The design of the machine, i.e. annular construction with large hollow shaft, was chosen to satisfy the constraints for the integration into the existing propulsion pod and to meet the reference nominal torque and speed for the inner propeller design. Detailed simulation of losses, including the effect of PWM modulation, was performed to assess the machine losses and to define the optimal switching frequency suitable for the drive. The study then focused on the fault operation capability by calculating the radial force acting on the machine rotor under different fault scenarios.


2020 - PMSM-Model-Based Sensorless Control of Hybrid Stepper Motors: Performance and Robustness to Parameters Dispersion [Relazione in Atti di Convegno]
Carfagna, E.; Migliazza, G.; Immovilli, F.; Verrelli, C. M.; Lorenzani, E.
abstract

Extended Kalman Filters (EKFs), Phase Locked Loops (PLLs), and Stator Flux Observers (SFOs) are widely used for sensorless control of Permanent Magnet Synchronous Motors (PMSMs) drives. Their use (in their most advanced version) is here extended, on the basis of model analogies and suitably-guaranteed closed loop stability properties, to the sensorless speed regulation control of Hybrid Stepper Motors (HSMs), in which position and speed sensors are not employed to reduce costs and increase robustness with respect to high temperature and high-vibration environments. Both realistic simulations and experimental results demonstrate the feasibility of the proposed methods in terms of closed-loop performance and robustness to parameters mismatch.


2020 - Reconfigurable Multi-Three-Phase Propulsion System for Naval Rim-Driven Propeller [Relazione in Atti di Convegno]
Alosa, C.; Immovilli, F.; Lorenzani, E.
abstract


2020 - Single-phase current source inverter with reduced ground leakage current for photovoltaic applications [Articolo su rivista]
Migliazza, G.; Lorenzani, E.; Immovilli, F.; Buticchi, G.
abstract

Integrated power electronics for photovoltaic applications has attracted increasing interest, due to the possibility of having grid-connected photovoltaic modules with independent maximum power point tracking and high reliability. In this paper, a single-phase Current Source Inverter (CSI) is discussed for a photovoltaic application. The basic CSI topology will be explained for the sake of completeness, highlighting its main features and analyzing the ground leakage current problem, an important benchmark for photovoltaic application. A novel topology, called CSI5, is proposed in this work. The main feature is the presence of additional switches for ground leakage current reduction. The performance of the proposed topology is assessed by numerical simulation, and the experimental results confirm that this solution is able to strongly reduce the ground leakage current and conduction power losses.


2019 - Analytical Equivalent Circuit Model for Series-Compensated Wireless Power Transfer Systems [Relazione in Atti di Convegno]
Benatti, D.; Migliazza, G.; Fornari, R.; Lorenzani, E.; Buticchi, G.
abstract


2019 - CSI and CSI7 current source inverters for modular transformerless PV inverters [Articolo su rivista]
Lorenzani, E.; Migliazza, G.; Immovilli, F.; Buticchi, G.
abstract


2019 - Critical Aspects and Strategies for Sensorless Control of IPMSM based on Low-Frequency Voltage Injection [Relazione in Atti di Convegno]
Brugioni, R.; Carfagna, E.; Lorenzani, E.; Immovilli, F.
abstract

High-Frequency signal injection is widely adopted for zero and low-speed operating conditions in sensorless control of Interior Permanent Magnet Synchronous Motors (IPMSM) drives. However, the audible noise emissions caused by induced HF current has restricted in some cases its practical application. Low-frequency signal injection solve the noise problem, but it introduces new issues. In particular, the filtering for signal separation is not trivial and affects negatively the current control loop and the dynamic performance of the angle tracking estimator. To overcome these limitations, some new strategies and modifications respect to the traditonal sensorless control are proposed in this paper, using the esteem of specific signal components estimated from known information of the drive. The simulations were carried out considering a discrete-time controller and quantiziers on measured currents and pulsed voltages. The results demonstrated the feasibility of the proposed method.


2019 - Internal Current Return Path for Ground Leakage Current Mitigation in Current Source Inverters [Articolo su rivista]
Lorenzani, E.; Migliazza, G.; Immovilli, F.; Gerada, C.; Zhang, H.; Buticchi, G.
abstract

This paper analyzes in detail the effect of a simple solution for ground leakage current mitigation applicable to transformerless three-phase current source inverter (CSI). The circuit modification solution is assessed for both traditional CSI topology and for CSI with an additional seventh switch, in literature named CSI7 (or H7), in particular with the splitting of the dc input inductance. In the present work, the solution is applied to grid-connected converters for string photovoltaic applications: scope of the circuit modification is to provide an internal return path from the wye connected capacitors of the output CL filter. This additional return path is able to significantly reduce the ground leakage current without adversely affecting THD. The performance of the proposed solution is assessed by the numerical simulations in case of a string of photovoltaic (PV) modules and the different behavior of CSI and CSI7 topologies is thoroughly investigated. Furthermore, the definition of V-cmZC is assessed by applying it to the common mode equivalent circuits for CSI7 with additional return path and their validation by means of a two-step simulation. The simulation results and experimental validation shows good agreement and confirm that the proposed solution is able to strongly reduce the ground leakage current.


2019 - Modular Multi-Three-Phase Electric Drives for Enhanced Reliability and Current Ripple Minimization [Relazione in Atti di Convegno]
Alosa, C.; Immovilli, F.; Lorenzani, E.
abstract


2019 - The Rebirth of the Current Source Inverter: Advantages for Aerospace Motor Design [Articolo su rivista]
Madonna, V.; Migliazza, G.; Giangrande, P.; Lorenzani, E.; Buticchi, G.; Galea, M.
abstract

It is well known and widely accepted that the voltage source inverter (VSI) now dominates the world of electrical drives. Its success is probably due to its simplicity, high efficiency, and the widespread availability of VSs. This popularity has, in turn, influenced the evolution of the semiconductor industry, which has focused in recent years on devices tailored for VSIs. Thus, products such as depletion devices (normally off) and those without reverse voltage blocking have been widely marketed and used.


2019 - Wide Voltage Range Dual Active Bridge PV Retrofit Storage System [Relazione in Atti di Convegno]
Fornari, R.; Immovilli, F.; Lorenzani, E.
abstract

This paper presents a storage system integration on the photovoltaic module side of a traditional grid-connected PV plant. The proposed retrofit application is based on a wide voltage range Dual Active Bridge topology, used as bidirectional DC/DC converter. Wide voltage operation capability at PV side is required to allow the integration of the retrofit storage system on a broader range of existing PV plants, characterized by different PV string operating voltage and commercial grid-connected inverters. Dual Active Bridge topology was chosen as a galvanically-insulated bidirectional single stage conversion stage to interface storage batteries to the PV side of the existing photovoltaic plant. The storage battery is charged during the overproduction of the PV plant and the storage system sustains the end-user domestic loads when solar irradiation is insufficient. The proper operation of the commercial inverter, the design and control strategy of the whole system showed the effectiveness of the proposed solution. A full-size 3.2kW converter prototype was manufactured and experimental validation was carried out.


2018 - AMPLIFICATORE PER IL PILOTAGGIO DI UN CARICO CAPACITIVO [Brevetto]
Migliazza, Giovanni; Lorenzani, Emilio; Larcher, Luca
abstract

La presente invenzione riguarda in generale il settore dell’elettronica. Più in particolare, la presente invenzione riguarda un amplificatore di tipo ibrido parallelo per il pilotaggio di un carico capacitivo, come ad esempio testine di stampa piezoelettriche.


2018 - Control Strategies for Class-E Resonant Inverter with Wide Load Variation [Relazione in Atti di Convegno]
Reatti, A; Corti, F; Pugi, L; Kazimierczuk, Mk; Migliazza, G; Lorenzani, E
abstract

The main advantage of resonant converters is the soft-switching conditions (SSC). The switching losses can be drastically reduced turning the power devices at zero-voltage switching (ZVS) or zero-current switching (ZCS). This allows to operate at higher switching frequency and to reduce the components size. Unfortunately, this condition can be achieved only at an optimal operating point. For example, if load variation occurs, the achievement of SSC is not guaranteed, producing more switching losses and therefore reducing the system efficiency. To overcome this problem and ensure ZVS over a wide load variation, two control strategies are presented. Their application to a ClassE inverter is investigated, but the principle can be applied to all resonant converters. Both control methods are based on components variations. The first technique changes the inductance L while the second one changes the capacitances C and C-1. The control algorithms are carried out and simulation results are given to validate the proposed algorithms.


2018 - Critical Aspects of Hybrid PFM-PWM Operation in LLC Converters For Electric Vehicles [Relazione in Atti di Convegno]
Fornari, R; Migliazza, G; Lorenzani, E; Immovilli, F
abstract

In an Electric Vehicle a galvanically insulated auxiliary power module of suitable power size is employed to interface the high-voltage main energy storage battery to the low voltage auxiliary loads. Such converter must be reliable, efficient and compact. Resonant converters have reached widespread application as they are characterized by high efficiency and low Electromagnetic Interference (EMI). Resonant converters are usually operated in Pulse Frequency Modulation (PFM) with fixed duty cycle. In case of high power applications characterized by wide output voltage regulation, Pulse Width Modulation (PWM) can be beneficially adopted to extend the continuous modulation operation at low output voltage / low output power. This work analyses drawbacks and critical aspects of use of PWM along with some modulation strategies able to minimize hard switching commutations in this operating condition. After a first analytical comparison, different PWM strategies are evaluated by means of numerical simulations and experimentally assessed. A Quasi-Resonant control is proposed and assessed by means of simulation, resulting in an effective solution to hard switching commutation.


2018 - Ground Leakage Current Mitigation for Three-Phase Current Source Inverters [Relazione in Atti di Convegno]
Lorenzani, E; Migliazza, G; Immovilli, F
abstract

This paper presents a simple solution for ground leakage current mitigation applicable to transformerless three-phase Current Source Inverter (CSI). The proposed solution is addressed only for CSI topology with an additional seventh switch, in literature named CSI7 (or H7), in particular with the splitting of the DC input inductance. In this paper the solution is applied to grid-connected converters for string photovoltaic applications. The proposed approach is to provide an internal return path from the wye-connected capacitors of the output CL filter. Thanks to CSI7 topology and modulation technique, this additional return path is able to significantly reduce the ground leakage current without adversely affecting power conversion efficiency and THD. The performance of the proposed solution is assessed by numerical simulations in case of strings with a different number of PV modules. Simulation results and preliminary experimental validation show that the proposed solution is able to strongly reduce the ground leakage current.


2018 - Persistency of excitation and position-sensorless control of permanent magnet synchronous motors [Articolo su rivista]
Verrelli, Cristiano Maria; Tomei, Patrizio; Lorenzani, Emilio
abstract

In this brief, the exponential rotor position tracking/regulation problem for position-sensorless (nonsalient-pole surface) PMSMs with unknown constant load torque and stator resistance is addressed. The requirement of persistency of excitation conditions involving a non-definitely zero rotor speed reference is removed, owing to the design of an innovative (speed measurement-based) adaptive observer that relies on a local version of the persistency of excitation lemma and does not involve straightforward adaptations of previous ideas.


2018 - Steady-state speed sensor fault detection in induction motors with uncertain parameters: A matter of algebraic equations [Articolo su rivista]
Verrelli, Cristiano Maria; Lorenzani, Emilio; Fornari, Raffaele; Mengoni, Michele; Zarri, Luca
abstract

This paper moves in the context highlighted in the recent literature, in which full and partial rotor speed sensor faults in induction motors with uncertain parameters can be detected by a single adaptive observer. Certain relevant experimental evidences concerning the use of such single adaptive observer in the aforementioned context, however, are yet to be theoretically motivated. Such evidences go beyond the already presented analyses and refer to the convergence of the resulting observer estimates under generating operations. In this paper, we present an algebraic equations-based analysis that extends any previous one, by providing a definite answer to the above question. It simultaneously clarifies any structural intrinsic limitation that is related to previously proposed approaches. The key point relies on deriving the explicit expressions for two admissible motor model solutions, which are characterized by the same output (rotor speed and stator currents) and input (stator voltages) profiles and whose existence is definitely linked to the adaptive observer behaviour in speed sensor fault detection scenarios.


2017 - CSI7: a Modified Three-phase Current Source Inverter for Modular Photovoltaic Applications [Articolo su rivista]
Lorenzani, Emilio; Immovilli, Fabio; Migliazza, Giovanni; Frigieri, Matteo; Bianchini, Claudio; Davoli, Matteo
abstract

This paper analyzes the performance of a gridtied, wide power range, transformerless, modified threephase Current Source Inverter (CSI), named CSI7. The CSI7 topology is here analyzed along with a suitable Space Vector Modulation (SVM) strategy able to attenuate the excitation of the output CL filter. The theoretical analysis and simple analytic expressions highlighted the performance and limitations of the topology when employed as a singlestage PV inverter, with particular emphasis on injected grid currents distortion and ground leakage current values. The inverter wide input range allows interfacing PV strings of different module count with a simple closed loop control. The principle of operation and control is described, the viability of the CSI7 topology was assessed with simulations and extensive experiments on a full-size laboratory prototype.


2017 - Further results on nonlinear tracking control and parameter estimation for induction motors [Articolo su rivista]
Verrelli, C. M; Tomei, P.; Lorenzani, Emilio; Fornari, Raffaele; Immovilli, Fabio
abstract

The original contribution of this paper, which concerns induction motors with uncertain constant load torque and rotor/stator resistances, is twofold. The first innovative contribution relies on the experimental analysis of the latest theoretically-based sensorless/output feedback solutions to the problem of tracking rotor speed and flux modulus reference signals with the simultaneous estimation of the uncertain parameters. The second novel contribution is constituted by the proof of existence for a new adaptive local flux observer from rotor speed and stator currents/voltages, which, in its full-order or reduced-order-like versions, involves neither over-parameterizations nor non-a priori verifiable first order stator resistance identifiability conditions at steady-state.


2017 - Ground leakage current in PV three-phase current source inverter topologies [Relazione in Atti di Convegno]
Lorenzani, E.; Migliazza, G.; Immovilli, F.; Bianchini, C.; Buticchi, G.
abstract

Current source inverter (CSI) is a family of power converters which has been recently investigated for photovoltaic power conversion in grid-tied operation, due to the inherent boost capability and ease of control. This paper assess Photovoltaic three-phase Current Source Inverters by two different CSI topologies and space vector modulation commutation strategies. Different CSI solutions are therefore analyzed by means of numerical simulations and the results are compared in terms of ground leakage current and THD of the injected grid currents. Extensive simulation results show that the CSI7 topology can improve the common mode performance while at the same time increasing the efficiency of the conventional CSI, at the price of a negligible added complexity.


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 - Nonlinear tracking control for sensorless permanent magnet synchronous motors with uncertainties [Articolo su rivista]
Verrelli, C. M; Tomei, P.; Lorenzani, Emilio; Migliazza, Giovanni; Immovilli, Fabio
abstract

The recent advanced solution in Marino, Tomei, and Verrelli (2013) to the tracking control problem for sensorless IMs with parameter uncertainties is translated on the basis of letter swap connections between the models of (nonsalient-pole surface) permanent magnet synchronous motors (PMSMs) and induction ones (IMs). The (stability proof-based) nonlinear adaptive position/speed tracking control for sensorless PMSMs (with simultaneous estimation of uncertain constant load torque and stator resistance), which is accordingly obtained by exploring and decoding the design paths in Marino et al. (2013) and which surprisingly represents a simple generalization of the controller in Tomei and Verrelli (2011), constitutes an innovative solution to the related open problem. Illustrative experimental results are included.


2016 - Ground leakage current reduction in single-phase current source inverter topologies [Relazione in Atti di Convegno]
Migliazza, Giovanni; Lorenzani, Emilio; Immovilli, Fabio; Bianchini, Claudio
abstract

This paper presents a grid-tied single phase photovoltaic microinverter based on Current Source Inverter (CSI) topology. The main topic of this work is related to the identification of a topology and a PWM strategy able to minimize the obvious issues of the basic CSI solution: efficiency and ground leakage current. The strong reduction of this last issue allows the use of the proposed solution in conjunction with Photovoltaic module in building integrated installations. Simulation results and a low voltage experimental validation present the effectiveness of the proposed solution in mitigating ground leakage currents.


2016 - Nonlinear adaptive control for position-sensorless permanent magnet synchronous motors with uncertainties [Relazione in Atti di Convegno]
Verrelli, Cristiano Maria; Tomei, Patrizio; Lorenzani, Emilio
abstract

In this paper we show that, when the rotor position is not measured in (nonsalient-pole surface) PMSMs with unknown constant load torque and stator resistance (with the rotor speed being available along with the stator currents), it is possible to guarantee exponential rotor position tracking and-mainly-regulation without resorting to persistency of excitation conditions which involve a non-definitely zero rotor speed reference. A new output feedback control is accordingly designed, which relies on a novel adaptive observer. The only price to be paid is constituted by a non-constant reference for the stator current vector d-component.


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 - Space-learning tracking control for permanent magnet step motors [Articolo su rivista]
Verrelli, Cristiano Maria; Tomei, Patrizio; Consolini, Luca; Lorenzani, Emilio
abstract

Repetitive space-learning controls are designed for current-fed uncertain permanent magnet step motors with non-sinusoidal flux distribution (the family of permanent magnet synchronous motors with cogging torque is allowed as a special case). Either semi-global rotor speed tracking is asymptotically achieved or local rotor position tracking is asymptotically guaranteed without requiring the time-periodicity of the corresponding reference signals. Simulation results illustrate the effectiveness of the presented approach in a typical electric drive control scenario, even in the presence of stator current dynamics which have been neglected at the design stage.


2015 - Active Rectifier With Integrated System Control for Microwind Power Systems [Articolo su rivista]
Buticchi, Giampaolo; Lorenzani, Emilio; Immovilli, Fabio; Bianchini, Claudio
abstract

This paper presents simple and effective control strategies for the active rectifier stage (AC/DC stage) of a grid-connected low power system for micro wind applications employing Permanent Magnet Synchronous Generator (PMSG). In particular a novel algorithm for the estimation of the rotor angle of the PMSG, based on flux estimators, was implemented using an adaptive low-pass filter coupled with a feed-forward compensator. This enabled a very smooth start-up operation of the PMSG, obtained by pre-loading the values of the flux estimator and using a single voltage transformer (VT) transducer. The solution for the power flow control between the active rectifier and the other(s) power converters connected to the common DC link was implemented without any digital communication between them, in order to obtain a solution suitable for modular architectures (e.g. to be used in conjunction with a grid-connected converter and/or an energy storage system). Simulation and experimental results confirmed the effectiveness of the proposed solutions. The experimental validation was conducted using a grid-connected converter as load for the proposed active rectifier.


2015 - Evaluation of combined reference frame transformation for interturn fault detection in permanent-magnet multiphase machines [Articolo su rivista]
Immovilli, Fabio; Bianchini, Claudio; Lorenzani, Emilio; Bellini, Alberto; Fornasiero, Emanuele
abstract

This paper focuses on modeling and experimental validation of a diagnostic fault classification procedure for interturn fault detection in permanent-magnet (PM) multiphase machines designed for fault-tolerant electric drives. The diagnostic procedure is based on the symmetrical component theory and relies upon the combined space vector D that gathers information from the two original space vectors obtained with different reference frames. The diagnostic index effectiveness and robustness were also investigated against other fault types such as rotor eccentricities and magnet damage to assess its discrimination capability. The proposed procedure was experimentally evaluated for the interturn fault case on a five-phase PM machine. Experiments were carried out at different speed and load levels, with increasing numbers of short-circuited turns. Both simulation and experimental results demonstrated the feasibility of the proposed diagnostic method.


2015 - Low cost PM synchronous servo-applications employing asynchronous-motor frame [Relazione in Atti di Convegno]
Bianchini, Claudio; Davoli, Matteo; Pellegrino, Gianmario; Immovilli, Fabio; Lorenzani, Emilio
abstract

This paper presents a comparison among low cost permanent magnet synchronous machine (PMSM) solutions, employing the frame and the stator laminations of an asynchronous machine. The comparison is carried out by means of finite element simulations. This work aims at obtaining machines with reduced cost, competitive in terms of nominal torque, torque ripple and cogging torque. The baseline for comparison is a surface mounted PMSM with high-strength magnets and non-skewed rotor. In order to reduce torque ripple and cogging torque, magnets with sinusoidal profiles radial wise are first introduced. Second, enhanced hybrid permanent magnets poles are adopted, replacing part of high strength NdFeB material with cheaper ferrite to reduce the production costs of the magnetic pole. Finally these PMSMs are compared to a synchronous reluctance and ferrite-assisted synchronous reluctance machines. The presented results indicate that the hybrid-magnets solution is the best trade-off between performance, cost and manufac-turability and that the ferrite-assisted synchronous reluctance machine is quite competitive and low cost.


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 - Active Common-Mode Filter for Ground Leakage Current Reduction in Grid-Connected PV Converters Operating With Arbitrary Power Factor [Articolo su rivista]
Barater, D.; Buticchi, G.; Lorenzani, Emilio; Concari, C.
abstract

This paper proposes a solution for reducing the ground leakage current in transformerless single-phase gridconnected photovoltaic converters. This is obtained with the introduction of an active common-mode filter able to compensate for variations of the output common-mode voltage of the power converter. The active common-mode filter is applied to a widespread and efficient full-bridge driven by a three-level pulse width modulation, allowing the power converter to operate with low ground leakage current and with an arbitrary power factor. After showing the desired voltage waveform for common-mode voltage compensation, this paper presents the design guidelines for the needed additional magnetic component together with the power loss considerations for all the devices added for the proposed solution. Experimental results show the performance of the proposed solution in terms of ground leakage current reduction, effectiveness of dead-time compensation, total harmonic distortion of the injected grid current, and power losses.


2014 - Design optimization for torque ripple minimization and poles cost reduction with hybrid permanent magnets [Relazione in Atti di Convegno]
Bianchini, Claudio; Davoli, Matteo; Immovilli, Fabio; Lorenzani, Emilio
abstract

This paper presents design strategies for the optimized design of the rotor poles in synchronous permanent magnet machines. The strategies are aimed at the reduction of torque ripple and cogging torque. Sinusoidally rounded magnet and rotor step-skewing are investigated, then a new proposal to reduce the cost of magnetic pole made in rare earth is presented. The goal is to introduce into a rotor pole, a fraction of low cost ferrite magnets on either side of the main rare earth NdFeB permanent magnet. The design procedure begins with some analytical consideration that allows to optimize the geometrical design of the magnets. Using Finite Element (FE) simulations, the effectiveness of the analytical model is verified and the results of the various methods are compared.


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 - Active Filter for the Removal of the DC Current Component for Single-Phase Power Lines [Articolo su rivista]
Buticchi, G.; Consolini, L.; Lorenzani, Emilio
abstract

Non-linear loads and grid connected converters can cause, besides the generation of several current harmonics in the grid current, a DC current component injection. A DC current component can cause the magnetic core saturation of distribution power transformers. Transformers operating under saturation conditions present increased power losses, overheating and distorted current waveforms. Since a DC current component causes a small DC voltage component drop across the parasitic resistance of the distribution grid conductors, canceling the DC voltage component at the Point of Common Coupling (PCC) implies the compensation of the DC current component injected/absorbed by electric loads or grid connected converters connected at the same PCC. This paper proposes a low cost nonlinear sensor for an accurate detection, free from offset problems, of the DC voltage component present in the grid voltage. The detection of the DC voltage component was used to realize an active filter of the DC current component. The proposed solution is outlined and then the stability issue is addressed by means of a simplified model. Experimental results confirmed that the simplified model closely approximates the real system.


2013 - Axial Flux Permanent Magnet Machine Desing and Optimization Using Multi Layer 2D Simulation [Relazione in Atti di Convegno]
Bianchini, Claudio; Immovilli, Fabio; Lorenzani, Emilio; A., Bellini; L., Felici
abstract

This paper presents the design of an axial flux permanent magnet machine for in-wheel application. The machine design and optimization are developed using two-dimensional (2-D) multi-layer finite element analysis approach. The threedimensional model of the machine has been approximated with a set of simulations in which the two-dimensional geometrical parameters were varied appropriately in order to reproduce the actual three-dimensional magnetic behavior. During design optimization, special attention was paid to the reduction of flux linkage harmonic content and to the reduction of cogging torque through the change of the permanent magnet profile and dimensions. Finally, a prototype machine was built to validate the effectiveness of the proposed method.


2013 - Detection Method of the DC bias in Distribution Power Transformers [Articolo su rivista]
G., Buticchi; Lorenzani, Emilio
abstract

Non-linear loads such as AC drives switch-mode power supplies and grid-connected converters can cause, besides the generation of unwanted current harmonics, a DC current component injection into the grid. This DC current component can lead to magnetic saturation of the distribution power transformers, leading to higher current distortion and overheating. This paper presents a method to detect the DC current component flowing into the distribution power transformer with a precise measurement of the DC voltage component at the transformer winding. A magnetic sensor has been developed and implemented in a closed-loop control system to achieve a high sensitivity and guarantees a good linearity with a high rejection ratio to grid voltage variations. Simulation and experimental results confirm the effectiveness of the proposed approach.


2013 - Experimental Evaluation of Combined Reference Frames Transformation for Stator Fault Detection in Multi-Phase Machines [Relazione in Atti di Convegno]
Bianchini, Claudio; Immovilli, Fabio; Lorenzani, Emilio; Bellini, Alberto; E., Fornasiero
abstract

This paper focuses on the modeling and experimental validation of a diagnostic index for fault detection in multiphase machines. Experiments are carried out on of a five-phase permanent-magnet machine designed for fault tolerant applications. The diagnostic index is aimed at stator faults detection and is based upon the combination of information from two different reference frames. The diagnostic index effectiveness and robustness are assessed by Finite Element analysis and experiments.


2013 - Performance Analysis of a Modified Current Source Inverter for Photovoltaic Microinverter Applications [Relazione in Atti di Convegno]
Lorenzani, Emilio; Immovilli, Fabio; Bianchini, Claudio; A., Bellini
abstract

This paper analyzes the performance of a grid-tied photovoltaic module integrated, transformerless, three-phase Current Source Inverter (CSI). The design exploits CSI inherent step-up capability to obtain a single stage power interfacing between the low voltage PV input and the high AC voltage output, to be fed into the distribution grid. A modified CSI converter topology is proposed along with a suitable PWM strategy and a simple closed loop control. The theoretical analysis and simple analytic expressions highlighted the performance and limitations of the topology when employed in single-stage PV microinverter supplied by a single low voltage PV panel. The principle of operation and control is described, and the traditional CSI topology has been simulated numerically in Matlab/Simulink environment. Results obtained with the proposed topology are presented and evaluated in order to validate the theoretical assumptions.


2013 - Power Losses Analysis in Interleaved Flyback Based PV Grid Connected Micro-Inverters [Relazione in Atti di Convegno]
Causo, Alberto; Salati, Andrea; Lorenzani, Emilio; Immovilli, Fabio; Bianchini, Claudio
abstract

This paper analyzes the power losses of photovoltaic micro-inverters based on flyback topology. A double secondary winding flyback converter topology was considered to inject alternating current into the grid. The purpose of this work is the identification and quantification of the different power losses present in a simple flyback topology and in the interleaved version with two different control strategies. The power losses comparison was carried out after designing a 250 W power converter using commercial, low cost components. Simulations in Matlab/Simulink environment highlighted the effectiveness of the interleaved architecture.


2012 - A Nine-Level Grid-Connected Photovoltaic Inverter Based on Cascaded Full-Bridge with Flying Capacitor [Relazione in Atti di Convegno]
Buticchi, G.; Concari, C.; Franceschini, G.; Lorenzani, E.; Zanchetta, P.
abstract

This paper proposes a nine-level PWM gridconnected photovoltaic inverter for single-phase applications. The basic structure relies on two cascaded full-bridges supplied with different voltage levels. A flying capacitor provides the power supply for the lower voltage full-bridge. In order to increase the efficiency and keep the ground leakage current under control, a specific PWM strategy was developed and an additional leakage current reduction circuit was added to the basic structure of the cascaded full-bridge. Moreover, the regulation of the flying capacitor voltage is taken into account. Simulations and experimental results confirm the good performance of the proposed solution.


2012 - Active Common-Mode Filter for Photovoltaic Transformerless Inverters [Relazione in Atti di Convegno]
Buticchi, G.; Barater, D.; Lorenzani, Emilio; Salati, Andrea
abstract

In the recent years the research on photovoltaic converters has been focused on topologies that do not feature a line frequency transformer, in order to reduce costs and successfully increase the overall efficiency. The main problem in removing the galvanic isolation is that the parasitic capacitance present between the cell and the metal frame enclosing the panel (usually earth-connected) enables a common-mode current to be injected into the grid by the converter. This paper proposes an active common-mode filter able to compensate the high-frequency common-mode voltage variations at the output of the power converters, that represent the principal cause of ground leakage current. The advantage of this solution concerns the capability to operate with an arbitrary power factor. In this work it is applied in cascade to a converter with standard full-bridge topology driven by a three-level PWM strategy. Simulation and experimental results shows the feasibility of the proposed approach.


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 - 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 - Dynamic Modeling of Double Cage Induction Machines for Diagnosis of Rotor Faults [Relazione in Atti di Convegno]
Lorenzani, Emilio; Salati, Andrea; Bianchini, Claudio; Immovilli, Fabio; Bellini, Alberto; Lee, S. B.; Yoo, J.; Kwon, C.
abstract

Double cage induction motors are typically employed in applications that require high starting torque for frequent, loaded starts. This makes the starting (outer) cage susceptible to fatigue failure since it must withstand the large thermo-mechanical stress associated with the high starting current and long acceleration time. Conventional FFT-based spectrum analysis techniques are insensitive to outer cage faults due to the small outer cage current under steady state operation, and the fault indicators and thresholds applied to single cage rotors cannot be used. Therefore, there is a strong industrial need for research and development of analysis techniques and advanced fault detection algorithms for double cage machines. However, there are only a few publications that investigate double cage rotor faults. In this paper, a dynamic model for rotor cage faults in double cage motors, which is the first step towards double cage rotor fault research, is derived. A 7.5 Hp separate end ring fabricated copper double cage rotor is built for experimental verification of the proposed fault model (copper inner cage/brass outer cage). The tests performed under startup and steady state operation show that the proposed fault model can provide sufficient accuracy and can be used as the basis for interpretation of FFT results and development of advanced fault detection algorithms.


2012 - Micro Wind Turbine System Integration Guidelines PMSG and Inverter Front End Choices [Relazione in Atti di Convegno]
Bianchini, Claudio; Immovilli, Fabio; Lorenzani, Emilio; Bellini, Alberto; G., Buticchi
abstract

This paper is aimed at the modeling and simulation of wind power system, with particular emphasis on small wind turbines employing surface permanent magnet synchronous gen- erators (SPMSGs). Generator and inverter front-end interaction is analytically and numerically modeled, in order to evaluate the generator’s efficiency depending on its electric parameters, both during normal and power limited operation. Passive and active rectifier front-end are taken into account to assess the influence of power electronics front-end over system performances. The final target of this work is to determine design guidelines for small wind turbine system optimization. The analysis is carried out through simulations which take into account the interactions of the SPMSG’s electrical parameters and through the evaluation of the generator’s efficiency at different operating conditions and inverter front-end architectures. The data obtained was further validated with experimental characterization of two different system architectures.


2012 - Optimal System Control of a Back-to-Back Power Converter for Wind Grid-Connected Converter [Relazione in Atti di Convegno]
G., Buticchi; Lorenzani, Emilio; Bianchini, Claudio
abstract

The most common topology for micro wind turbine systems is composed of the wind turbine directly connected to a Permanent Magnet Synchronous Generator (PMSG) followed by a AC/DC/AC converter. The converter is realized with a AC/DC passive rectifier, a DC/DC boost converter and a DC/AC full-bridge inverter which injects the electric power into the grid. Considering the cost reduction of power switches and Digital Signal Processors (DSP), back-to-back inverter topologies have to be considered for new projects, since they allow to obtain better energy productivity of the wind systems. In this paper a complete solution based on back-to-back topology is presented. This solution includes the sensorless vector control for the PMSG, the Maximum Power Point Tracker (MPPT) algorithm, the d-q vector control of the single-phase grid connected inverter and the power flow control strategies from the PMSG to the grid. It is worth noticing that the two full-bridge power converters are controlled by two different DSP which can exchange information only through the value of the DC Link voltage. Experimental results confirm the effectiveness of the adopted solutions.


2012 - Review of Design Solutions for Internal Permanent Magnet Machines Cogging Torque Reduction [Articolo su rivista]
Bianchini, Claudio; Immovilli, Fabio; Lorenzani, Emilio; Bellini, Alberto; Davoli, M.
abstract

Internal permanent magnet synchronous machinesare spreading in industrial production.They feature high torque density and extended speed rangethat are key issues in many fields of applications, however theircogging torque is typically quite high.Many methods and design guidelines for cogging torquereduction exist in literature and this paper compares them. Forthis purpose, the different design guidelines are applied to acommon reference machine in order to assess their effectiveness.Computer Finite Element Analysis (FEA) are carried out for eachcase in order to compare the cogging torque reduction capabilityof the different techniques. The side effects of these techniques,such as back-emf and rated torque profile distortions, willbe taken into account. The paper contribution is to comparethe various cogging torque reduction techniques and magneticgeometries on a common reference machine to identify the mosteffective ones.


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 - Transformerless Grid-Connected Converter for PV Plants with Constant Common Mode Voltage and Arbitrary Power Factor [Relazione in Atti di Convegno]
Barater, D.; Buticchi, G.; Lorenzani, Emilio; Malori, V.
abstract

Many transformerless topologies for photovoltaic systems were proposed in order to minimize power losses and avoid high levels of ground leakage current (that can arise in such systems). The most efficient PWM strategies achieve this goal by decoupling the grid from the DC Link during the freewheeling phases of the output current. These strategies usually operate only with a unity power factor. However, as solar inverters have penetrated into power distribution networks, new issues have arisen and modifications of regulations governing grid connection of distributed systems were introduced in some countries. One of the new requirements for the inverters connected to the low-voltage grids is the possibility to provide reactive power. This paper proposes a transformerless inverter topology with a wide-range power factor operation. Simulation results and extensive experimental results, focused mainly on ground leakage current analysis, showed the effectiveness of the proposed solution.


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 Nonlinear Reactor for DC Current Compensation in Single Phase Power Lines [Relazione in Atti di Convegno]
G., Buticchi; L., Consolini; Lorenzani, Emilio
abstract

Non-linear loads and grid connected converters, whose utilization is constantly growing, have been causing problems regarding the power quality. These problems comprehend the generation of harmonics in the current provided by the power distributor. Among different kinds of deterioration, there is the issue of the DC current component. As a matter of fact, a DC current is detrimental for the distribution power transformer, as it leads to saturation the magnetic core. The saturation of the power transformer increases the VAR absorption, leading to possible damage the magnetic component due to overheating. This paper proposes a compensator system based on a non linear sensor that acts as an active filter for the DC current component flowing in the power lines. The paper is organized as follows: the first part outlines the strategy, then the stability issue is addressed by means of a simplified model. A simulation verification showed that the simplified model closely approximates the real system.


2011 - A Sensor to Detect the DC Bias of Distribution Power Transformers [Relazione in Atti di Convegno]
G., Buticchi; Lorenzani, Emilio
abstract

The widespread use of power converters in low-voltage distribution grids has given rise to issues regarding the power quality. In fact, non-linear loads such as AC Drives, switching-mode power supplies and grid-connected converters can cause, besides the generation of several current harmonics, also a DC current component injection into the grid. This DC current component can lead to magnetic saturation of the distribution power transformers; in this condition, the transformers present distorted current waveforms, increased power absorption and overheating, that can damage the transformer insulations. This paper presents a way to diagnose the magnetic saturation by a non-direct measurement of the DC current component flowing in the power transformer. In other words, the proposed solution provides an information about the total DC injection produced by the sum of all the electric devices connected to the distribution power transformer. The DC current component causes a DC voltage drop across the parasitic resistance of the transformer's winding: sensing this DC voltage drop allows to evaluate the DC current component. A magnetic sensor was developed in order to obtain a great sensitivity, and the implemented closed loop control allowed to guarantee a good linearity with a high rejection ratio of the grid voltage variations. Simulation and experimental results confirm the effectiveness of the proposed approach.


2011 - Homopolar Generators: an Overview [Relazione in Atti di Convegno]
Bianchini, Claudio; Immovilli, Fabio; Bellini, Alberto; Lorenzani, Emilio; C., Concari; M., Scolari
abstract

Homopolar generators are a particular class of electrical machines capable of generating DC current without the use of mechanical commutators or electronic rectifiers. This paper presents an overview of the typical configurations of homopolar DC machines. The paper focuses on generating operation, trying to assess the optimal configuration for a high efficiency generator. Among the possible solutions, a specific configuration which uses permanent magnets for the excitation field was chosen and built to perform a set of experiments.


2011 - Modeling and Analysis of a DC Current Compensator in Distribution Power Lines [Relazione in Atti di Convegno]
G., Buticchi; L., Consolini; C., Concari; Lorenzani, Emilio
abstract

In electrical grids, the widespread connection of power converters and non-linear loads caused the emergence of problems related to power quality. In particular, one important issue is the generation of DC current components. This phenomenon has various detrimental effects on the power distribution transformers, such as increased harmonic distortion, increased power losses, and possible damage due to consequent overheating. This paper proposes an analysis and modeling of a simple control system composed of a power converter and a DC voltage sensor, aimed at compensating the DC current component flowing in the grid. The proposed model allows to investigate the stability of the DC current compensation strategy. The simplified model was experimentally validated through the construction of a suitable test bed.


2011 - Modeling and Stability Analysis of an Active Filter for DC Current Compensation [Relazione in Atti di Convegno]
G., Buticchi; L., Consolini; Lorenzani, Emilio
abstract

The widespread use of power converters and nonlinearloads connected to the grid have caused the emergenceof problems regarding the power quality. Among differentkind of non-linear distortion, there is the issue of the DCcurrent component. In fact, a DC current component flowingin the grid transformers has various detrimental effects, i.e.increased harmonic distortion, increased power losses, andpossible damage due to consequent overheating. This paperproposes a non-linear sensor and a compensator system thatact as an active filter to remove the DC current componentflowing in the power lines. In the first part, the strategy isoutlined and then the stability issue is addressed by meansof a simplified model. Simulation results confirmed that thesimplified model closely approximates the real system. Anapproximated analysis of stability is also presented. Finally wepresent some experimental results that shows the effectivenessof the proposed solution.


2010 - A new proposal to eliminate the DC current component at the point of common coupling for grid connected systems [Relazione in Atti di Convegno]
G., Buticchi; Lorenzani, Emilio; A., Fratta
abstract

Nonlinear loads as grid connected converters can cause, besides the generation of several current harmonics in the grid current, a DC current component injection. A DC current component can cause the magnetic core saturation of distribution power transformers. Transformers operating under saturation conditions present increased power losses, overheating and distorted current waveforms. Since a DC current component causes a small DC voltage component drop across the parasitic resistance of the distribution grid conductors, canceling the DC voltage component at the Point of Common Coupling (PCC) implies the compensation of the DC current injection by electric loads or grid connected converters connected at the same PCC. This paper proposes a low cost solution for an accurate detection, free from offset problems, of the DC voltage component present in the grid voltage. The DC voltage compensation strategy was embedded in a full bridge grid connected converter. Simulation and experimental results showed the effectiveness of the proposed strategy.


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.


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 - 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 - “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 - 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 - 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 - 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 - 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.


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 - 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.


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.


2005 - Time Harmonics Investigation of Stator and Rotor Currents of a Dedicated Induction Machine [Relazione in Atti di Convegno]
L., Donadio; M., Zucca; C., Concari; Lorenzani, Emilio; Bellini, Alberto
abstract

Condition monitoring of electric machines is ofincreasing importance. The continuous assessment of themachine performance allows to schedule appropriatelymaintenance operations, thus increasing machineoperating life and reducing repair cost. The input currentspectrum is a wide spread procedure for non-invasive diagnosisof induction machines.Information on rotor variables are available only bycomputation, typically by FEM. Experimental results aredifficult to achieve: specific sensors must be mounted on therotor to detect currents or flux density.In this paper a dedicated machine and experimental set-up,developed at IEN, was used, that allows to detect single barcurrents through sensors positioned on the rotor bars. So doing itis possible to compute both rotor phase currents and space vectorspectra.The main phenomena, that introduce waveform distortion, arebriefly recalled and the corresponding spectrum lines for bothstator and rotor currents are reported and analyzed in thispaper.


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 - Experimental Validation of a Diagnostic Index for Induction Motors Stator Faults [Relazione in Atti di Convegno]
A., Bellini; M., Cavatorta; C., Concari; Lorenzani, Emilio; C., Tassoni; A., Toscani
abstract

Motor Current Signature Analysis (MCSA) is usedfor non-invasive diagnosis of incipient or actual faults of gridsupplied induction machine stator defects, being the negativesequence component of current space vector the diagnosticindex most widely used. Supply unbalance and load influenceof the machine however affect the negative component andthey may cause the failure of the diagnostic procedure,Recently, deceleration test that may remove some drawbacksof MCSA, has been proposed for rotor and stator faultdiagnosis,In this paper it is shown that the Residual VoltageSignature Analysis (RVSA) obtained by the deceleration testprovides, once removed the intrinsic manufacturingasymmetry, a diagnostic index directly related to thepercentage of shorted furits. The main advantage of RVSA isthnt any influence caused by the supply unbalance and load ismasked. Therefore a new diagnostic index is presented that isthe residual voltage negative sequence component. The novelindex performances have been proofed thanks to a simplifiedmodel of the faulted machine and experimentally validated bya special test motor that allows the introduction of differentshort circuits. This novel index can be used to confirm theMCSA-based diagnostic procedure developed by the sameauthors.


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 - 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.