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Giovanni MIGLIAZZA

Ricercatore Legge 240/10 - t.det.
Dipartimento di Scienze e Metodi dell'Ingegneria
Docente a contratto
Dipartimento di Scienze e Metodi dell'Ingegneria

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Pubblicazioni

2023 - Active Thermal Control for Lifetime Equalization in CSI7-based Modular Photovoltaic Integration System [Relazione in Atti di Convegno]
Peng, Q.; Buticchi, G.; Migliazza, G.; Tan, N. M. L.; Guenter, S.; Carfagna, E.; Fidone, G. L.
abstract

2023 - Common Architectures and Devices for Current Source Inverter in Motor-Drive Applications: A Comprehensive Review [Articolo su rivista]
Fidone, G. L.; Migliazza, G.; Carfagna, E.; Benatti, D.; Immovilli, F.; Buticchi, G.; Lorenzani, E.
abstract

When compared to the much more common voltage-source inverter (VSI), the current-source inverter (CSI) is rarely used for variable speed drive applications, due to its disadvantages: the need of a constant DC-link current, typically realized with a front-end converter, and the need for reverse-voltage blocking (RVB) devices, typically implemented with in-series diodes. This limits the overall efficiency of the architecture. This paper investigates latest progress of the CSI research, with the aim of demonstrating why CSI could come back in the near future. Different architectures based on modern wide-bandgap (WBG) switches are analyzed, with an emphasis on why CSI can be advantageous compared to VSI.

2023 - Improved Speed Extension for Permanent Magnet Synchronous Generators by Means of Winding Reconfiguration [Articolo su rivista]
Zhou, X.; Yang, J.; Migliazza, G.; Guenter, S.; Wang, S.; Gerada, C.; Buticchi, G.
abstract

With the increased development of electrical subsystems onboard modern transportation platforms, e.g., more electric aircrafts or more electric ships, the need for electric generation systems has increased. Since many motors require electric starting capability, the application of the starter/generator has been the focus of several studies. The peculiarity of such a system is its requirement for high torque at low speed (for the starting) as well as an extended operation range during the normal generation operations. This mismatch between maximum torque and speed comes at the expense of the power density of the electronic converter, which needs to be designed for the worst case situation and, due to the electric machine optimization, often requires field weakening operations. A new winding reconfiguration is proposed to achieve speed extension and provide more potentiality for high-speed applications. This work compares different power trains in terms of efficiency current stress for electric machines. Hardware-in-the-loop results are adopted to verify the practical implementation of the control systems.

2023 - Novel Single-Stage Current Source Inverter: Extension to Low-Speed Region in Motor Drive Applications [Articolo su rivista]
Benatti, D.; Migliazza, G.; Carfagna, E.; Immovilli, F.; Lorenzani, E.
abstract

In motor drive applications, single-stage current source inverters (CSIs) can manage only a limited speed range when the output voltage is greater than input voltage, due to the intrinsic boost capability. The classical solution adopted in low-speed region to control the input dc current, consists in the insertion of a prestage power converter. This article proposes a single-stage CSI that replaces the input inductance Ldc with coupled inductor. In this way, it is possible to add the needed time interval for the discharge of the magnetic energy of primary inductance Lm when the converter works in low-speed region or at standstill, extending the operating region of the converter. This solution allows to increase the efficiency of traditional CSIs for applications when the motor works most of the time in the high-speed region, thanks to the single-stage power conversion. Experimental and simulation results driving a permanent magnet synchronous machine are shown, confirming the validity of the proposed architecture.

2023 - Work in Progress: Output Impedance Specification of A Three-Phase Current-Source Inverter for Modular Photovoltaic Applications [Relazione in Atti di Convegno]
Peng, Q.; Migliazza, G.; Buticchi, G.; Guenter, S.; Tan, N. M. L.; Yang, J.; Wheeler, P.
abstract

Impedance-based stability assessment has been an important part of renewable integration. Modeling and measurement of impedance under Synchronized Reference Frame (SRF) is a common way for a portrait of the frequency-dependent impedance. In this paper, a modified current-source inverter (CSI) called CSI7 for photovoltaic (PV) integration is studied. The SRF admittance of the system under different solar irradiation from 400W/m2 to 1000W/m2 with a resolution of 100W/m2 is measured in PLECS simulation. It is found that large frequency-dependent admittance appears under the high-frequency zone of the q axis which could lead to harmonic instability problems.

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 - 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.

2022 - Stator Flux Observer for the Sensorless Speed Control of Synchronous Machines with Uncertain Torque Constant [Relazione in Atti di Convegno]
Carfagna, E.; Migliazza, G.; Bernardi, F.; Verrelli, C. M.; Lorenzani, E.
abstract

In this paper, a recently designed adaptive stator flux observer (SFO), which provides estimates of rotor position and torque constant for surface mounted permanent magnet synchronous machines (PMSMs), is included in a speed sensorless control. Simulations and experimental results are carried out in order to evaluate the robustness of the whole control architecture with respect to uncertainties in the electrical parameters of the motor, as well as to the mismatch between the actual stator voltages imposed to the PMSM and the ones used for the observer, especially when low speeds are involved.

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 - Failure modes and reliability oriented system design for aerospace power electronic converters [Articolo su rivista]
Harikumaran, J.; Buticchi, G.; Migliazza, G.; Madonna, V.; Giangrande, P.; Costabeber, A.; Wheeler, P.; Galea, M.
abstract

Aircraft electrification has been a major trend in aviation industry for past 20 years. Given the increasing electrical power requirement for future more electric aircraft and hybrid electric aircraft, research efforts has been ongoing in high power electrical conversion for air-borne systems. Safety critical nature of aviation systems places reliability of aerospace power converters as a critical design concern. In this paper, power electronic system reliability is studied with emphasis on lifetime limiting factors of critical sub components. Reliability of voltage source power converters at different system voltage levels are modelled for a starter generator drive converter. A key observation is that Si IGBT devices are sufficient with respect to reliability requirements in low and medium voltage systems (up to 540 V). At higher system voltages (above 540 V), multi level topologies are necessary for designing with Si IGBTs. In constant power profile drive, system reliability is minimally affected by wear-out failure of film capacitors in converter DC links. In multi level topologies without enhanced voltage derating, system reliability is dominated by cosmic ray induced random failures. Simulation results demonstrate that at high system voltages (810 V), 2 L topology with SiC mosfets outperform Si IGBT based 3 L topology with respect to reliability.

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.

2021 - Review of Speed-Extension of Permanent Magnet Synchronous Motor with Reconfigurable-Winding System [Relazione in Atti di Convegno]
Zhou, X.; Buticchi, G.; Migliazza, G.; Wang, S.; Galea, M.; Gerada, C.
abstract

The traditional MTPA cannot satisfy the practical speed commands in traction application, the field weakening and reconfigurable topologies can achieve the speed extension. This paper provides a comparative summary of different reconfiguration topologies for speed extensions and provides a brief discussion of the previous research. Then, to evaluate the different topologies function, three models with the same output power are established to observe the performance. The experimental results represent the series/parallel configurations supply the lowest drive losses and highest efficiency without using the demagnetizing component. Meanwhile, the future study which combines the series/parallel configuration with field weakening is pointed out.

2020 - A Time-Saving Approach for the Thermal Lifetime Evaluation of Low-Voltage Electrical Machines [Articolo su rivista]
Madonna, V.; Giangrande, P.; Migliazza, G.; Buticchi, G.; Galea, M.
abstract

Modern electrical machines, such as those employed in transportation applications are required to provide very high performance in terms of power (and torque) density and efficiency. The reality, however, is that the more these machines are 'pushed' in relation to power density, the more is the probability of failure of their insulation systems, through enhanced electrical and thermal stresses. On the other hand, regardless the power density level, the electrical machine still needs to respect the certification processes set by the international standards and procedures. Unfortunately, today reliability and lifetime are still not considered as main design objective functions right from the start of the design process. This is a direct result of a gap in knowledge in terms of the precise understanding of failure mechanisms. If physics of failure models are available, then reliability can be included at all design stages. Therefore, this article proposes a method that shortens the time demanded for the thermal lifetime evaluation procedure or qualification of low-voltage electrical machines. The theory behind the method is presented and, then, experimentally validated on custom designed specimens.

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 - 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 - Reliability oriented thermal management of aircraft power converters [Relazione in Atti di Convegno]
Harikumaran, J.; Buticchi, G.; Migliazza, G.; Wheeler, P.; Galea, M.
abstract

On board electrical power generation continue to increase as more aircraft systems are being electrified. Increasingly power converters are the interface of power generation and electrical loads in aircrafts. Reliability of aircraft power electronics is essential for high reliability and mission critical applications. Along with wear-out failure mechanisms, random failure modes must also be addressed to realize high reliability aerospace power converters. A dominant random failure mode in aerospace environment is due to cosmic rays (CR). In this work, a thermal management approach is proposed to maximize reliability of the converters considering CR failure mode. The proposed thermal controller is validated with an experimental setup. In the discussion, the trade-off involved between wear-out and CR induced failure mode is addressed.

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 - 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 - On the Thermal Insulation Qualification of Low Voltage Electrical Machines [Relazione in Atti di Convegno]
Madonna, V; Giangrande, P; Migliazza, G; Buticchi, G; Galea, M
abstract

Electrical motors are required to perform reliably for a certain number of hours/cycles. Assuming the insulation breakdown as the predominant source of failure, then the lifetime of an electrical machine can generally be said to correspond to that of its weakest insulation sub-system. Among all the insulation stressing factors, thermal aging is a primary source of progressive deterioration, and, eventually, failure. In order to guarantee a satisfactory lifetime, motors are designed to have thermal operational points which are always lower than their insulation thermal class. However, this design choice does not allow to maximize the exploitation of the insulation lifetime capability. Technical standards report methods for the thermal qualification of electrical machines based on accelerated thermal aging tests. Such assessment, despite enabling the insulation lifetime estimation, might require several thousand hours of testing. This paper, therefore, proposes and validates a new methodology which considerably shortens the thermal qualification of electric motors.

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.

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.

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 - 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 - 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.