Nuova ricerca

DAVIDE BARATER

Professore Associato presso: Dipartimento di Ingegneria "Enzo Ferrari"


Home | Curriculum(pdf) | Didattica |


Pubblicazioni

- 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).


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

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


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

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


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

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


2021 - Hairpin windings: Sensitivity analysis and guidelines to reduce ac losses [Relazione in Atti di Convegno]
Preci, E.; Gerada, D.; Degano, M.; Buticchi, G.; Gerada, C.; Nuzzo, S.; Barater, D.
abstract

Nowadays, electrification in the transportation sector is one of the most viable solutions to reduce CO2 emissions and meet fuel economy requirements. Being the electrical machine one of the most important players in this electrification trend, extensive research is currently being dedicated to the improvement of their efficiency and power density. In automotive applications, hairpin technologies are widely spreading due to their potential in reducing costs and life cycles in a mass production perspective, as well as in increasing the torque capabilities of machines. However, several challenges need to be addressed before the complete replacement of random windings with hairpins can take place. Of these challenges, the loss produced during high frequency operations is one of the most limiting. This paper aims at studying and investigating high frequency (AC) losses for different slot geometries and conductor cross sections, which in turn involve the analysis of different slots-per-pole-per-phase / layers-per-slot combinations. In addition, the effects on the AC losses of reducing the slot fill factor are studied, either by removing the closest conductors to the slot opening or by reducing the hairpin legs' height. Analytical and numerical models are employed to investigate these concepts.


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

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


2021 - Partial Discharge Phenomena in Electrical Machines for the More Electrical Aircraft. Part II: Impact of Reduced Pressures and Wide Bandgap Devices [Articolo su rivista]
Lusuardi, L.; Rumi, A.; Cavallini, A.; Barater, D.; Nuzzo, S.
abstract

This paper focuses on the inception of partial discharges within the insulation system of electrical actuators used for the More Electrical Aircraft (MEA). Since these machines should operate in the absence of Partial Discharges (PDs), the dependence of the PD Inception Voltage (PDIV) on voltage impulses typical of wide bandgap (SiC) devices is investigated at both 1 bar, reduced pressures close to those typical of aircraft cruising altitudes (150 mbar - 200 mbar) or lower (down to 5 mbar). Propagation issues are not dealt with here as results were obtained working on insulation models consisting of couples of wires twisted together (twisted pairs), thus knowing exactly the potential differences between all points of the insulation model. The results show that the rise times and the switching frequencies associated with wide bandgap devices have little impact on the PDIV. A model able to predict the PDIV of the turn/turn insulation of random wound motors (the most vulnerable part of the insulation) at different pressures is proposed. The model is also able to deal with temperature changes, with limitations that depend on the type on insulation systems.


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

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


2021 - Partial Discharges in Electrical Machines for the More Electrical Aircraft. Part III: Preventing Partial Discharges [Articolo su rivista]
Rumi, A.; Lusuardi, L.; Cavallini, A.; Pastura, M.; Barater, D.; Nuzzo, S.
abstract

In this paper, the results obtained from lab tests on twisted pairs subjected to different voltage waveforms and atmospheric conditions are used to propose how to modify the IEC Std. 60034-18-41. The goal is to make the standard suitable for the More Electrical Aircraft (MEA). The results show that it is initially necessary to screen out materials through simple tests. The enhancement factors for temperature can be modified to consider reduced pressures and temperatures using a simple model. The aging enhancement factor can be reduced considering the reduced sensitivity of the partial discharge inception voltage (PDIV) at low pressures on the enamel thickness. Eventually, reference will be made to the drive discussed in Part I of this series to draw conclusions about the likelihood of partial discharge inception in a random wound stator and how to reduce it by modifying either the inverter or the stator insulation. Reference to a random wound motor is made throughout the paper.


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

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


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

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


2020 - High-Speed Electric Drives: A Step Towards System Design [Articolo su rivista]
Savi, Filippo; Barater, Davide; Nardo, Mauro Di; Degano, Michele; Gerada, Chris; Wheeler, Pat; Buticchi, Giampaolo
abstract


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

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


2020 - Multiphase fault tolerant distributed control techniques for integrated drives based on resonant regulators [Relazione in Atti di Convegno]
Savi, F.; Barater, D.; Buticchi, G.; Wheeler, P.; Gerada, C.
abstract

One of the challenges brought forward by the gradual electrification undertaken by the aviation sector is the requirement of fault tolerance for machine drive systems to be used for critical on-board tasks such as propulsion or primary flight surface actuation. Their inherent advantages in both volumetric and gravimetric power density makes integrated drives the prime candidates for these applications. Despite the large advances in this field, few key area still need work. Key among which is fault tolerant current control strategies. This paper studies the application of resonant control techniques to achieve a scalable and fault tolerant current control strategy for multiphase machine.


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

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


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

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


2019 - An Improved Automatic Voltage Regulator for Self-Excited, Small-to-Medium Power Generating Sets equipped with Brushless Excitation Systems [Relazione in Atti di Convegno]
Nuzzo, Stefano; Bolognesi, Paolo; Galea, Michael; Barater, Davide
abstract

The classical, wound-field, synchronous generator is currently enjoying a revamped interest in its design and development, partly due to the ever-increasing requirements in terms of power quality standards, efficiency and power density and partly due to advances in materials and manufacturing techniques. Also, the significant improvements in the computational resources allow the utilization of modern design techniques and tools. Apart from the design of the machine itself, another area of interest is the system-level optimization. The proposed project is aimed at renewing the power electronics and the control logics in power generating sets featuring the popular brushless configuration. An industrial small-to-medium size power generating set is taken as case study. The considered platform is first analyzed at system-level, by modelling in detail all of the components comprised in it. Then, focus is given to the automatic voltage regulator. A faster, more flexible and more efficient system is proposed, based on a 4-quadrant DC-to-DC converter which permits to improve the dynamic response of the excitation system.


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

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


2019 - Dv/Dt Filtering Techniques for Electric Drives: Review and Challenges [Relazione in Atti di Convegno]
Pastura, Marco; Nuzzo, Stefano; Kohler, Mario; Barater, Davide
abstract

The use of wide band gap devices in power converters is becoming more and more popular since they enable operations at higher switching frequencies, voltages and temperatures compared to traditional power semiconductors, while also improving the efficiency. However, in electric drives, they also tend to increase voltage overshoots at motor terminals and to produce uneven voltage distributions across stator windings, due to their high rate of voltage change over time (dv/dt). In order to mitigate these issues, passive filters can be employed. The aim of this paper is to give an overview of possible solutions based on passive filters, analyzing the main advantages and drawbacks. A comprehensive, qualitative comparative study is carried out taking into account common mode currents reduction, power losses, costs, dimensions and reliability.


2019 - Information technologies for distributed machine drives: An overview [Relazione in Atti di Convegno]
Savi, F.; Buticchi, G.; Gerada, C.; Wheeler, P.; Barater, D.
abstract

The exponential growth experienced by the semiconductor manufacturing field has led to a large proliferation of devices with large amounts computational power, enabling countless technologies and revolutionizing many fields. Control systems and machine drives are certainly among them. Much research is being carried out to develop multi-phase and fully segmented machines, with their inherent fault tolerance. To take full advantage of the redundancy and load sharing capabilities of the machine structure, with multiple winding sets, a suitable distributed control method must be used. A high performance network between the drives is thus required. This paper will present an overview of the available communication protocols that are used in the field and evaluate how suitable are they to this new class of very demanding real time tasks.


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

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


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

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


2019 - Wide Bandgap Voltage Source Inverter Design for Automotive Electric Drivetrain [Relazione in Atti di Convegno]
Savi, F.; Buticchi, G.; Gerada, C.; Wheeler, P.; Barater, Davide
abstract

In this paper a high power, high frequency voltage source inverter for automotive traction application is reviewed. The main objectives of the design process is the maximization of power density, while keeping high efficiency and low weight. In this paper, the focus is placed on the peculiarities that differentiate this design from other ordinary machine drive. In particular several areas are explored, all equally important for the achievement of design goals. Starting from device choice to gate driving and current sensing circuits design.


2018 - A PV-Inspired Low-Common-Mode Dual-Active-Bridge Converter for Aerospace Applications [Articolo su rivista]
Buticchi, Giampaolo; Barater, Davide; Costa, Levy Ferreira; Liserre, Marco
abstract

In the framework of the more electric aircraft, the use of isolated dc-dc power conversion for the electrical power distribution system is one of the most investigated solutions. If the dc-dc converter produces a variable common-mode voltage, the leakage current can flow in the interwinding parasitic capacitance of the high-frequency transformer, leading to insulation deterioration and early failure. This paper proposes to use modified H-bridge structures, already employed in the photovoltaic system for dc-ac power converters, to enable a constant common-mode voltage for isolated dc-dc converters. The analysis shows that this solution can achieve the same efficiency as the conventional one, while simulations and experiments show a strong reduction of the common-mode current flowing through the transformer. A reliability analysis showed that the lifetime of the high-frequency transformer can be extended with the proposed solution.


2018 - A Quadruple Active Bridge Converter for the Storage Integration on the More Electric Aircraft [Articolo su rivista]
Buticchi, Giampaolo; Costa, Levy Ferreira; Barater, Davide; Liserre, Marco; Amarillo, Eugenio Dominguez
abstract

The More Electric Aircraft concepts aims at increasing the penetration of electric systems on aircrafts. In this framework, the electrical power distribution system (EPDS) is of high importance. In order to improve the utilization of the generators and face the peak power demand without disconnecting the loads, different technologies of storage are employed. This paper proposes the use of a quadruple active bridge converter, already employed in other fields, to interface a fuel cell, a battery, and a supercapacitor bank to the dc bus of the EPDS. This objective can be achieved by employing multiple dc/dc converters, which allow an individual control of the energy sources and a good efficiency. Obtaining the same power control and efficiency with a multiport power converter constitutes a challenge that is worth taking to reduce cost, volume, and weight and increase the system reliability. A novel control based on proportional integral (PI) controllers in conjunction with a decoupling system and current feedforward allow shaping the power request to each port. This, however, leads to an asymmetrical loading of each port, which could decrease the efficiency. A laboratory prototype is used to confirm that this asymmetrical kind of operation, where each port processes a different amount of power, does not imply a marked reduction of efficiency.


2018 - A Quadruple Active Bridge converter as the storage interface in the more electric aircraft [Relazione in Atti di Convegno]
Buticchi, Giampaolo; Costa, Levy; Barater, Davide; Liserre, Marco; Dominguez, Eugenio
abstract

The More Electric Aircraft (MEA) concepts aims at increasing the penetration of electric systems on the aircrafts. In this framework, the electrical power distribution system (EPDS) is of high importance. Increasing the electrical subsystem while limiting the overall weight is one of the major challenges for the MEA. This problem can be addressed by a proper energy storage system that allows increasing the utilization of the generators. This paper proposes the use of a Quadruple Active Bridge (QAB) converter, already adopted in other fields, to interfaces different storage technologies to the aircraft DC bus. This solution would replace multiple DC/DC converters, increasing the power density, but presents difficulty in the power flow control and in the possible efficiency deterioration in the case of asymmetrical operation. A novel control, based on current feed-forward and power decoupling is proposed to this aim and simulations shows the effectiveness of the solution. A laboratory prototype is used to confirm that the asymmetrical operation, where each port processes a different amount of power, does not imply a marked reduction of efficiency.


2018 - Influence of impulse voltage repetition frequency on RPDIV in partial vacuum [Articolo su rivista]
Meyer, Doris Ragna; Cavallini, Andrea; Lusuardi, Luca; Barater, Davide; Pietrini, Giorgio; Soldati, Alessandro
abstract

The reliability of low-voltage inverter-fed motors is highly dependent on the inception of partial discharges. The effect of impulsive waveform parameters must be investigated to predict the repetitive partial discharge inception voltage (RPDIV) and define test procedures that can indicate properly the behavior in service of the insulation system. This paper focuses on the RPDIV of magnet wires using twisted pairs subjected to repetitive unipolar impulsive voltage waveforms. The effects of supply frequency (5 to 200 kHz) at pressure levels that are typical for aircraft (20 to 100 kPa) is examined. Results show that RPDIV steadily decreases with frequency up to 100 kHz where it reaches a plateau. This behavior is explained as an effect of the oscillations that inevitably exist in the applied voltage waveform. Therefore, a conservative estimate of the RPDIV could be achieved by raising the supply frequency well above the operation frequency. In the experiments, the RPDIV is decreasing linearly with pressure. If this behavior could be confirmed for other insulation systems, the design of systems working at pressures typical of aircraft would result relatively easy.


2018 - Response to Discussion of 'A Modular Speed-Drooped System for High Reliability Integrated Modular Motor Drives' [Articolo su rivista]
Galassini, Alessandro; Costabeber, Alessandro; Degano, Michele; Buticchi, Giampaolo; Gerada, Chris; Barater, Davide
abstract

The authors appreciate the interest shown in our paper. In the paper under discussion [1], a distributed speed control strategy suitable for multi-three-phase machines with enhanced power sharing capability is presented. The focus of the manuscript is on the power sharing transient controllability achieved by using a sharing regulator based on the droop controller, which was introduced for the first time by Fingas and Lehn [2]. In [1], the authors added the outermost loop in charge of restoring the drooped output speed. The overall control strategy and the design procedure of each loop - current, sharing, and speed - is presented and validated by means of experimental results. Two off-the-shelf three-phase induction machines coupled on the same shaft and controlled by a custom inverter were loaded by a third off-the-shelf three- phase induction machine.


2017 - A system level comparison of drive topologies for high speed electrical machines [Relazione in Atti di Convegno]
Savi, Filippo; Barater, Davide; DI Nardo, Mauro; Degano, Michele; Gerada, Chris
abstract

This paper presents a comprehensive comparative study among five different converter topologies all designed to drive a 8.5kW-120krpm surface permanent magnet synchronous machine. The study aims at comparing the considered systems in terms of converter complexity, control complexity and overall efficiency. The assessment of the subsystems' efficiencies is based on a set of decoupled converter-electrical machine simulations. First the designed converters are simulated in Matlab-Simulink environment in order to estimate the converter losses and the current waveforms. Then the latter are used to supply the Finite Elements(FE) model of the electrical machine so to estimate all the loss components present in the real scenario. The results of the carried out study gives a wide understanding of the interaction between the two subsystems and some general design considerations needed to select the converter topology.


2017 - Active thermal control by controlled shoot-through of power devices [Relazione in Atti di Convegno]
Soldati, Alessandro; Concari, Carlo; Barater, Davide; Iannuzzo, Francesco; Blaabjerg, Frede
abstract

Active Thermal Control (ATC) consists in driving power switches in a less efficient way when low load conditions are present. The resulting wasted power is used to self-heat the device, reducing amplitude and occurrence of thermal cycles and hence improving the reliability. This paper presents a novel way to control losses, and hence temperature, of both positive- and negative-current devices in half-bridge topologies at various load conditions. The goal is achieved by means of a controlled shoot-through of the half-bridge leg.


2017 - Active thermal control for reliability improvement of MOS-gated power devices [Relazione in Atti di Convegno]
Soldati, Alessandro; Concari, Carlo; Dossena, Fabrizio; Barater, Davide; Iannuzzo, Francesco; Blaabjerg, Frede
abstract

This paper proposes an Active Thermal Control (ATC) method for MOS-gated power switches aimed at reducing temperature swing amplitude during operation. It leverages on the fact that thermal cycle amplitude of many actuation system components (such as power devices) has a large impact on the system reliability and lifetime. These figures can then be improved, which eases the adoption of electrification in markets, such as transportation, where they are still below target values. The proposed ATC method leaves electric load parameters untouched, while acting dynamically on gate parameters, namely voltage and resistance. A model-predictive control (MPC) strategy is used to determine the most suitable parameters to use. Simulations of the control scheme are presented first, to predict the potential benefits on temperature swing amplitude, and the consequent improvements in terms of device lifetime are inferred, using literature models. Then, experimental proof of concept is presented and discussed, together with its limitations and drawbacks.


2017 - H8 architecture for reduced common-mode voltage three-phase PV converters with silicon and SiC power switches [Relazione in Atti di Convegno]
Concari, L.; Barater, D.; Concari, C.; Toscani, A.; Buticchi, G.; Liserre, M.
abstract

This paper presents a three-phase converter architecture with a reduced common mode voltage to be used in photovoltaic power systems. The full-bridge architecture is modified by adding two additional switches in the DC path that allow decoupling the load from the source during the freewheeling phases. Optimized modulation strategies are analyzed and compared against the space vector modulation for the full-bridge. Extensive measurements show an improved efficiency when SiC devices are used, and a theoretical analysis links this efficiency to a marked extension of the converter lifetime.


2017 - Incipient Fault Diagnosis in Ultrareliable Electrical Machines [Articolo su rivista]
Barater, Davide; Arellano-Padilla, Jesus; Gerada, Chris
abstract

Early detection of incipient faults in ac drives is one of the most difficult challenges for condition monitoring, especially for faults related to insulation degradation of the windings. In low power motors, the insulation degradation is principally due to the steep voltage variations caused by the voltage source converters that drive the machines. In the last years, with the coming to market of new no-Si based power devices, which achieve great values of dv/dt, fast tracking of electrical fault has became a topic of primary importance. In this paper, a new method to detect the presence of incipient faults in ultrareliable electric machines is presented and compared with a previous solution. The different methods were extensively evaluated by means of experimental results. It is shown that potential winding faults can be detected at an early stage of fault inception and thus measures can be taken to limit propagation.


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

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


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

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


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

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


2017 - Thermal stress mitigation by Active Thermal Control: Architectures, models and specific hardware [Relazione in Atti di Convegno]
Soldati, Alessandro; Dossena, Fabrizio; Pietrini, Giorgio; Barater, Davide; Concari, Carlo; Iannuzzo, Francesco
abstract

This work proposes an Active Thermal Control (ATC) of power switches. Leveraging on the fact that thermal stress has wide impact on the system reliability, controlling thermal transients is supposed to lengthen the lifetime of electronic conversion systems. Indeed in some environments, such as transportation, reliability and lifetime are still obstacles to widespread adoption of electric and electronic actuators, despite a general trend of electrification spreading in many different areas of interest. Active thermal control is attained leaving the electric parameters of load untouched, while acting dynamically on gate parameters (voltage and resistance), by means of a specifically designed gate driver. Two different control algorithms, sharing similar model and hardware, are presented: one is based on a linear controller, while the other relies on a model-predictive control (MPC) strategy. Simulation results of control schemes are presented, together with evaluation of the proposed loss models. Experimental proof of the ability of the proposed control to reduce thermal swing and related stress on the device is presented, too.


2017 - Wavelet-based prognostic-oriented temperature sensing with sigma-delta ADCs in power applications [Relazione in Atti di Convegno]
Pietrini, Giorgio; Soldati, Alessandro; Barater, Davide; Concari, Carlo
abstract

Thermal stress is one of many possible failure causes of power electronics systems; thermal cycles are known to produce mechanical fatigue on power electronic devices, thus leading to their failure in time. Temperature swing can be somehow controlled, if some decrease in efficiency can be tolerated by the power system, changing gate driver parameters to heat up the device in low load conditions. This is known as Active Thermal Control (ATC). To implement ATC, the temperature information of devices is needed. Since this sensing is carried out near power conductors, switched at high frequency, strong disturbances will affect the reading. This paper proposes a new signal-conditioning scheme based on discrete wavelet transform (DWT) and compares it to some established filtering techniques to assess which is most suitable for the application. Hints about insulation of measuring equipment will be given, too. Moreover, the possibility offered by the algorithms to store long-Time temperature information (through compression of incoming data) will be described, as large-span observation can help prognostic algorithms in forecasting the remaining useful life of the power apparatus.


2016 - A Modular Speed-Drooped System for High Reliability Integrated Modular Motor Drives [Articolo su rivista]
Galassini, Alessandro; Costabeber, Alessandro; Gerada, Chris; Buticchi, Giampaolo; Barater, Davide
abstract

Future transportation challenges include a considerable reduction in pollutant emissions at a time when significant increase in demand is predicted. One of the enabling solutions is the electrification of transport systems as this should lead to improved operability, fuel savings, emission reduction, and maintenance. While state-of-the-art technology has demonstrable benefits there needs to be considerable advancement to meet future transportation affordability and emission targets. Primarily, electrical drives need an improved power density, an increased reliability, and a reduced specific cost. For this reason, integrated modular motor drives (IMMDs) present an attractive solution. Modularity leads to redundancy and easier integration. This paper presents a novel speed-drooped control system applied to motors fed by modular paralleled converters. This control technique allows precise speed regulation and power sharing among different segments showing improved fault tolerance and reliability. The design procedure and the power sharing dynamic have been presented and analyzed by means of MATLAB/Simulink and validated in a 3-kW experimental rig, showing good agreement with the expected performances.


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

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


2016 - Analysis of the frequency-based control of a master/slave micro-grid [Articolo su rivista]
Buticchi, Giampaolo; Carne, Giovanni De; Barater, Davide; Zou, Zhixiang; Liserre, Marco
abstract

Renewable energy penetration in the low-voltage grid faces several limitations due to the current grid topology. Master/slave micro-grids could help solving these issues, by offering additional services to the grid such as the power management of the distributed power energy sources. In some cases, the power produced by the distributed energy sources exceeds the local consumption of the low-voltage grid. The consequent reverse power flow can be either dangerous (for the medium voltage) or impossible (for a micro-grid with limited storage). The droop characteristic of commercial inverter can be exploited to avoid this behaviour. However, stability problems can arise due to a low phase-locked-loop (PLL) bandwidth. This study investigates the stability of this solution depending on the bandwidth of the PLL of the distributed power generation sources.


2016 - Closed-form approach for predicting overvoltage transients in cable-fed PWM motor drives for MEA [Relazione in Atti di Convegno]
Pietrini, Giorgio; Barater, Davide; Concari, Carlo; Galea, Michael; Gerada, Chris
abstract

The More Electric Aircraft (MEA) concept has set tight constraints for power density and efficiency of electromechanical actuators in aircraft applications. In order to comply with these high power standards, new wide-bandgap (SiC and GaN) semiconductor devices may be exploited. Unfortunately, the extremely short switching times of these devices can easily trigger high frequency ringing voltage at motor terminal in cable-fed PWM motor drives due to pulse reflection. The resultant overvoltage stresses the insulation of stator windings decreasing the motor's lifespan. The most common solutions involve bulky and heavy passive filters, not suitable for MEA design approach, so the overvoltage suppression remains an open question. This paper explores the influence of pulse rising (and falling) time to the magnitude of motor terminal overvoltage through a detailed closed-form analysis of the problem in order to support electrical drive design optimization.


2016 - Comparison of flux observers for sensorless control of permanent magnet assisted SynRel motors [Relazione in Atti di Convegno]
Concari, Luca; Toscani, Andrea; Barater, Davide; Concari, Carlo; Degano, Michele; Pellegrino, Gianmario
abstract

This paper proposes the comparison among different sensorless position estimation strategies suitable for permanent magnet assisted synchronous reluctance machine drives. A machine of such type was designed and optimized aiming at improving its sensorless performance, besides minimizing the torque ripple and maximizing the power factor. Different sensorless solutions for the estimation of the magnetic flux linkage and for tracking the rotor angle are investigated and their performance compared in computer simulations. Experimental results are reported for the PM-assisted synchronous reluctance motor drive example.


2016 - H8 inverter for common-mode voltage reduction in electric drives [Articolo su rivista]
Concari, Luca; Barater, Davide; Buticchi, Giampaolo; Concari, Carlo; Liserre, Marco
abstract

This paper presents a modified two-level three-phase inverter for the reduction of the leakage current. With respect to a traditional two-level inverter, the proposed solution reduces the common-mode voltage (CMV), both in amplitude and frequency. Between the dc source and the traditional three-phase bridge, two active dc-decoupling devices and a voltage-clamping network have been added. A dedicated control strategy was developed adopting a modified space vector pulse-width modulation, oriented to the reduction of the CMV. Simulations showing the good performance of the solution are presented. A preliminary prototype was developed and experimental results are presented.


2016 - Investigation on the common mode currents in a smart transformer-fed low-voltage grid [Relazione in Atti di Convegno]
Barater, Davide; Concari, Luca; Buticchi, Giampaolo; Liserre, Marco
abstract

The Smart Transformer (ST) represents an enabling technology for providing new services to Low Voltage (LV) and Medium Voltage (MV) grid, overcoming the problems that are limiting the widespread diffusion of distributed renewable sources in conventional distribution systems. The ST 3-stage configuration includes a DC/AC 4-wires converter at the LV side, that must be able to cope with the equipment already installed in the LV grid in which ST wants to substitute conventional distribution transformer. Grid converters with capacitance towards ground, when connected to ST-fed LV grid can cause common mode current problems not yet discussed in the literature. This paper aims to fill this gap through an in-depth analysis of the problem and indicating possible solutions.


2016 - Performance Evaluation of a Three-Level ANPC Photovoltaic Grid-Connected Inverter With 650-V SiC Devices and Optimized PWM [Articolo su rivista]
Barater, Davide; Concari, Carlo; Buticchi, Giampaolo; Gurpinar, Emre; De, Dipankar; Castellazzi, Alberto
abstract

Photovoltaic (PV) energy conversion has been on the spotlight of scientific research on renewable energy for several years. In recent years, the bulk of the research on PV has focused on transformerless grid-connected inverters, more efficient than traditional line transformer-based ones, but more critical from a power quality point of view, especially in terms of ground leakage current. Neutral-point-clamped (NPC) inverters have recently gained interest due to their intrinsically low ground leakage current and high efficiency, especially for MOSFET-based topologies. This paper presents an active NPC (ANPC) topology equipped with 650-V silicon carbide (SiC) MOSFETs, with a new modulation strategy that allows to reap the benefits of the wide-bandgap devices. An efficiency improvement is obtained due to the parallel operation of two devices during the freewheeling intervals. Simulations and experimental results confirm the effectiveness of the proposed converter.


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 - Review of oscillating water column converters [Articolo su rivista]
Delmonte, Nicola; Barater, Davide; Giuliani, Francesco; Cova, Paolo; Buticchi, Giampaolo
abstract

Ocean waves are a huge, largely unexploited energy resource and the potential for extracting energy from waves is great. Research in this area is driven by the need to meet renewable energy targets, but it is relatively immature compared to other renewable energy technologies. This review introduces some device types that represent the state of the art of Oscillating Water Column (OWC) technology, a kind of Wave Energy Converter (WEC). Unlike other works in literature, typically limited to specific aspects of WECs, in this paper will be pursued a system wide perspective, from the sea waves to the grid connection.


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

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


2016 - Stability and performance analysis of a voltage controlled resistor circuit for wide band-gap device gate drivers [Relazione in Atti di Convegno]
Soldati, Alessandro; Pietrini, Giorgio; Barater, Davide; Concari, Carlo
abstract

Wide band-gap devices are making inroads in the power converters scenario, and specific circuits to drive these components are actively under development. The purpose of this paper is to analyze, from the stability and dynamic performance point of view, a Voltage Controlled Power Resistor (VCPR), that can be used to control the gate resistance of the device driver with values over a continuous range. Parametric analysis, SPICE simulations and experimental outcomes are presented, in order to determine circuit characteristics. Results show that the proposed topology is stable under a wide range of electric parameters, and suggest that the circuit bandwidth can be tuned in order to benefit from the VCPR in a wide band-gap device gate driver.


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

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


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

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


2015 - A novel three-phase inverter for common-mode voltage reduction in electric drives [Relazione in Atti di Convegno]
Concari, Luca; Barater, Davide; Concar, Carlo; Buticchi, Giampaolo
abstract

This paper presents an active solution for the elimination of the leakage current, in a three-phase PWM inverter drive. With respect to a traditional three-phase bridge, the proposed solution reduces the common-mode voltage variations, both in amplitude and frequency. A novel architecture for the inverter is presented. Between the DC source and the traditional three-phase bridge, two active DC-decoupling devices and a voltage-clamping network have been added. A dedicated control strategy was developed adopting a modified Space Vector PWM modulation, oriented to the reduction of the common-mode voltage variations in the proposed topology. Simulations showing the good performance of the solution are presented. A preliminary prototype was developed and experimental results are presented.


2015 - A voltage controlled power resistor circuit for active gate driving of wide-bandgap power devices [Relazione in Atti di Convegno]
Soldati, Alessandro; Barater, Davide; Concari, Carlo; Galea, Michael; Gerada, Chris
abstract

Wide-bandgap devices are under the spotlight of scientific research as they exhibit great performance in terms of efficiency and temperature operation. However, to fully exploit their characteristics, dedicated driving circuits are needed. High-power gate-insulated switching devices exhibit important input capacitance; when fast switching speeds are demanded, high-current pulses are needed to drive the gate terminal. This is particularly true for wide-bandgap devices, capable of lower transition times than conventional silicon devices. The proposed circuit is a voltage controlled resistor, which output can drive wide-bandgap devices. Design criteria, as well as simulation results, are presented.


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

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


2015 - Design of a control unit for advanced gate drivers featuring adaptive dead-time and diagnostics [Relazione in Atti di Convegno]
Soldati, Alessandro; Barater, Davide; Brugnano, Francesco; Concari, Carlo
abstract

The growing demand for high-performance power converters calls for the adoption of new strategies, not only in architectures, but also in electronic technologies. To take full advantage of wide-bandgap semiconductor (SiC, GaN) power devices, and to exploit their amazing capabilities, dedicated drivers need to be developed. This paper presents a control unit for advanced gate drivers, based on a finite-state machine (FSM), and discusses design criteria; the proposed design is verified by simulation in Matlab-Simulink. The presented automaton not only «follows» the power switch during its state transitions, but features also automatic dead-time insertion when the switch is operated in bridge configurations, and is able to provide important diagnostic and self-test information.


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

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


2015 - State space model of a modular speed-drooped system for high reliability integrated modular motor drives [Relazione in Atti di Convegno]
Galassini, Alessandro; Costabeber, Alessandro; Gerada, Chris; Buticchi, Giampaolo; Barater, Davide
abstract

Future transportation challenges include a considerable reduction in pollutant emissions at a time when significant increase in demand is predicted. One of the enabling solutions is the electrification of transport systems as this should lead to improved operability, fuel savings, emission reduction and maintenance. In this framework, the electrical power drivetrain is central. Whilst state-of-the-art technology has demonstrable benefits there needs to be considerable advancement to meet future transportation affordability and emission targets. Primarily, electrical drives need an improved power density, an increased reliability and a reduced specific cost. For this reason, Integrated Modular Motor Drives (IMMD) presents an attractive solution. Modularity leads to redundancy and easier integration. A novel speed-drooped control system applied to motors fed by modular converters is proposed. This control technique allows to control the speed and to share the power among different segments without any direct communication between the modules. The state space model is provided and validated with Matlab/Simulink.


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 - Comparison of different methods for incipient fault diagnosis in PMSMs with coaxial insulated windings [Relazione in Atti di Convegno]
Barater, Davide; Arellano-Padilla, Jesus; Gerada, Chris
abstract

Early detection of incipient faults in AC drives is one of the most difficult challenges for condition monitoring, especially for faults related to insulation degradation of the windings. In low power motors, the insulation degradations are principally due to the steep voltage variations caused by the voltage source converters (VSCs) that drive the machines. In the last years, the possibility to employ coaxial cables in the stator windings has been explored in order to enhance the capacity of the motors to withstand the great values of dv/dt that are achieved by the no-Si based power devices. In this paper a new method to detect the presence of incipient faults in PMSM with coaxial insulated winding is presented and compared with a previous solution. The different methods were extensively evaluated, by means simulations and experimental results, to determine their feasibility to be employed as on-line condition monitoring systems.


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

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


2014 - High-dynamic single-phase hilbert-based PLL for improved phase-jump ride-through in grid-connected inverters [Relazione in Atti di Convegno]
Giampaolo, Buticchi; Tarisciotti, Luca; Zanchetta, Pericle; Barater, Davide
abstract

The diffusion of renewable energy sources has now gained a very high importance in contributing to the electrical power needs. Grid-connected photovoltaic or wind energy conversion systems are nowadays highly integrated in the electrical grid, and they provide a consistent share of power to the nearby loads. Although this is true for high-power three-phase systems, problems related to the increasing penetration of low power, distributed generation systems into the grid structure have not been completely investigated yet. This paper proposes a control system based on a Hilbert-filter single-phase PLL with very fast response that allows the detection of fast frequency variations or phase jump in the grid voltage. The novelty resides in the use of a very short FIR transfer function to approximate the Hilbert filter in conjunction with a system that compensates the magnitude error. Simulations and experiments show that this system can be employed to increase the phase-jump ride-through capability of single phase grid-connected inverters.


2014 - Modular photovoltaic inverter with high-frequency DC/DC stage based on low-voltage FETs [Relazione in Atti di Convegno]
Giuliani, F.; Barater, D.; Concari, C.; Cova, P.; Delmonte, N.; Menozzi, Roberto; Buticchi, G.; Tarisciotti, L.
abstract

This paper proposes a multi-string DC/AC architecture for photovoltaic grid-connected converters intended using GaN FETs as switching devices. Three isolated DC/DC converters fed by separate strings supply the DC Link of a 7-level cascaded H-Bridge DC/AC multilevel inverter. Due to the great interest in power plants oriented to self-consumption, a DC/DC converter configuration with a battery system for energy storage is also considered. Extensive simulations of the control confirmed the capability of the architecture to handle the power flows required by the proposed application.


2014 - Oscillating water column power conversion: A technology review [Relazione in Atti di Convegno]
Delmonte, Nicola; Barater, Davide; Giuliani, Francesco; Cova, Paolo; Buticchi, Giampaolo
abstract

Ocean waves are a huge, largely unexploited energy resource, and the potential for extracting energy from waves is great. Research in this area is driven by the need to meet renewable energy targets, but it is relatively immature compared to other renewable energy technologies. This brief review introduces some device types that represent the state of the art of Oscillating Water Column (OWC) technologies, a kind of Wave Energy Converter (WEC). Unlike other works in literature, typically limited to specific aspects of WECs, in this paper will be pursued a system wide perspective, from the sea waves to the grid connection, with a particular focus on the power electronics.


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

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


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

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


2014 - Performance evaluation of a 3-level ANPC photovoltaic grid-connected inverter with 650V SiC devices and optimized PWM [Relazione in Atti di Convegno]
Barater, D.; Concari, C.; Buticchi, G.; Gurpinar, E.; De, D.; Castellazzi, A.
abstract

Photovoltaic energy conversion has been on the spotlight of scientific research for several years. Special attention was paid to the grid-connected inverters that do not feature an insulation transformer (transformerless topologies). In this framework, Neutral Point Clamped inverters have gained interest due to the low ground leakage current. Recently, the research has been focused on high-efficiency MOSFET-based topologies. In this paper an Active-NPC topology is equipped with 650V ROHM SiC devices. A new modulation strategy that allows to exploit the characteristics of Sic MOSFETs, is proposed. It permits to obtain very high efficiency due to the parallel operation of the devices during the freewheeling phases of the inverter output current. Simulation and experimental results show the benefits of this choice.


2014 - Winding concepts for ultra reliable electrical machines [Relazione in Atti di Convegno]
Arumugam, Puvan; Barater, Davide; Hamiti, Tahar; Gerada, Chris
abstract

This paper investigates two winding concepts for Permanent Magnet (PM) machines used for more electric aircraft systems where reliability is a concern. Analysis is carried out using two different surface mounted PM machines designed for low and high speed applications: a 12 slot, 10 pole machine with concentrated windings for rotorcraft swashplate actuation and a 36-slot 6-pole machine with distributed winding arrangement for an aircraft starter-generator. The impact of the winding arrangement for the low speed machine is investigated with a focus on turn-turn Short-Circuit (SC) faults. Implications of the SC fault and methods to restrain the resulting SC current are discussed. A prognostics method for potential turn-turn SC faults for the high speed application is then investigated. It is shown that potential winding faults can be detected at an early stage of fault inception and thus measures can be taken to limit propagation.


2013 - A simple deadbeat current control for single-phase transformerless inverters with LCL filter [Relazione in Atti di Convegno]
Buticchi, Giampaolo; Barater, Davide; Tarisciotti, Luca; Zanchetta, Pericle
abstract

Single-phase grid-connected converters are nowadays normally adopted in low-power and domestic applications. In order to improve the efficiency, while keeping the total cost of the system low, the converters are usually designed without an insulation transformer. Recently, these converters have witnessed an increased interest due to the widespread diffusion of renewable energy sources. In order to ensure the compliance with the international regulation for the grid connection, the Total Harmonic Distortion (THD) of the grid current must be maintained below specific thresholds indicated by the standards. For this reason, LCL filters allow to obtain a greater harmonic attenuation than a simple inductive filter. This paper proposes a deadbeat current control, specifically tailored for this application, which can ensure optimal reference tracking, rejection of the grid voltage disturbance and low computational effort. Simulation and experimental results show the effectiveness of the proposed solution. © 2013 IEEE.


2013 - Diagnosis of incipient faults in PMSMs with coaxially insulated windings [Relazione in Atti di Convegno]
Barater, Davide; Buticchi, Giampaolo; Gerada, Chris; Arellano-Padilla, Jesus
abstract

Early detection of incipient faults in AC drives is one of the most difficult challenges for condition monitoring, especially for faults related to insulation degradation of the windings. This is because insulation degradation is very difficult to be detected on-line, so these faults may pass unnoticed before turning into a major faults. This paper looks at the feasibility of using coaxially insulated windings not only to increase reliability against winding insulation problems, but as an alternative to advance condition monitoring that may be suitable for the detection of insulation degradation, and other faults not easily detected by conventional schemes such as demagnetization issues, and the presence of inter-turn short circuits. The concept of insulation degradation for the case of coaxially insulated windings is analytically considered in this work and a novel condition monitoring alternative proposed. The proposed scheme and winding topology are extensively evaluated numerical to determine their feasibility to drive condition monitoring. © 2013 IEEE.


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

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


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 - 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.


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.


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 - 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.