Wide Band Gap Devices and Their Application in Power Electronics

Power electronic systems have a great impact on modern society. Their applications target a more sustainable future by minimizing the negative impacts of industrialization on the environment, such as global warming effects and greenhouse gas emission. Power devices based on wide band gap (WBG) material have the potential to deliver a paradigm shift in regard to energy efficiency and working with respect to the devices based on mature silicon (Si). Gallium nitride (GaN) and silicon carbide (SiC) have been treated as one of the most promising WBG materials that allow the performance limits of matured Si switching devices to be significantly exceeded. WBG-based power devices enable fast switching with lower power losses at higher switching frequency and hence, allow the development of high power density and high efficiency power converters. This paper reviews popular SiC and GaN power devices, discusses the associated merits and challenges, and finally their applications in power electronics

Cost-Effective and High-Efficiency Variable-Speed Switched Reluctance Drives With Ring-Connected Winding Configuration

This paper presents a novel converter topology for six-phase switched reluctance motor (SRM) drives, which reduces the number of switches and diodes by half, compared with the conventional asymmetric half-bridge converter, but needs no additional energy storage component. A dynamic model of a six-phase SRM is developed in the MATLAB/SIMULINK environment and conventional current chopping and angle position control techniques are applied to the proposed converter, demonstrating successful operation across the full speed range with modified conventional control techniques, lower converter losses, and higher system efficiency compared with the asymmetric half-bridge converter. Experimental tests comparing two versions of the proposed converter with an asymmetric half-bridge are described and verify the predictions of the simulations

Multi-Objective Drive-Cycle Based Design Optimization of Permanent Magnet Synchronous Machines

Research conducted previously has shown that a battery electric vehicle (BEV) motor design incorporating drive-cycle optimization can lead to achievement of a higher torque density motor that consumes less energy over the drive-cycle in comparison to a conventionally designed motor. Such a motor indirectly extends the driving range of the BEV. Firstly, in this thesis, a vehicle dynamics model for a direct-drive machine and its associated vehicle parameters is implemented for the urban dynamometer driving schedule (UDDS) to derive loading data in terms of torque, speed, power, and energy. K-means clustering and Gaussian mixture modeling (GMM) are two clustering techniques used to reduce the number of machine operating points of the drive-cycle while preserving the characteristics of the entire cycle. These methods offer high computational efficiency and low computational time cost while optimizing an electric machine. Differential evolution (DE) is employed to optimize the baseline fractional slot concentrated winding (FSCW) surface permanent magnet synchronous machine (SPMSM). A computationally efficient finite element analysis (CEFEA) technique is developed to evaluate the machine at the representative drive-cycle points elicited from the clustering approaches. In addition, a steady-state thermal model is established to assess the electric motor temperature variation between optimization design candidates. In an alternative application, the drive-cycle cluster points are utilized for a computationally efficient drive-cycle system simulation that examines the effects of inverter time harmonics on motor performance. The motor is parameterized and modeled in a PSIM motor-inverter simulation that determines the current excitation harmonics that are injected into the machine during drive-cycle operation. These current excitations are inserted into the finite element analysis motor simulation for accurate analysis of the harmonic effects. The analysis summarizes the benefits of high-frequency devices such as gallium nitride (GaN) in comparison to insulated gate bipolar transistors (IGBT) in terms of torque ripple and motor efficiency on a drive-cycle

Special Power Electronics Converters and Machine Drives with Wide Band-Gap Devices

Power electronic converters play a key role in power generation, storage, and consumption. The major portion of power losses in the converters is dissipated in the semiconductor switching devices. In recent years, new power semiconductors based on wide band-gap (WBG) devices have been increasingly developed and employed in terms of promising merits including the lower on-state resistance, lower turn-on/off energy, higher capable switching frequency, higher temperature tolerance than conventional Si devices. However, WBG devices also brought new challenges including lower fault tolerance, higher system cost, gate driver challenges, and high dv/dt and resulting increased bearing current in electric machines. This work first proposed a hybrid Si IGBTs + SiC MOSFETs five-level transistor clamped H-bridge (TCHB) inverter which required significantly fewer number of semiconductor switches and fewer isolated DC sources than the conventional cascaded H-bridge inverter. As a result, system cost was largely reduced considering the high price of WBG devices in the present market. The semiconductor switches operated at carrier frequency were configured as Silicon Carbide (SiC) devices to improve the inverter efficiency, while the switches operated at fundamental output frequency (i.e., grid frequency) were constituted by Silicon (Si) IGBT devices. Different modulation strategies and control methods were developed and compared. In other words, this proposed SiC+Si hybrid TCHB inverter provided a solution to ride through a load short-circuit fault. Another special power electronic, multiport converter, was designed for EV charging station integrated with PV power generation and battery energy storage system. The control scheme for different charging modes was carefully developed to improve stabilization including power gap balancing, peak shaving, and valley filling, and voltage sag compensation. As a result, the influence on the power grid was reduced due to the matching between daily charging demand and adequate daytime PV generation. For special machine drives, such as slotless and coreless machines with low inductance, low core losses, typical drive implementations using conventional silicon-based devices are performance limited and also produce large current and torque ripples. In this research, WBG devices were employed to increase inverter switching frequency, reduce current ripple, reduce filter size, and as a result reduce drive system cost. Two inverter drive configurations were proposed and implemented with WBG devices in order to mitigate such issues for 2-phase very low inductance machines. Two inverter topologies, i.e., a dual H-bridge inverter with maximum redundancy and survivability and a 3-leg inverter for reduced cost, were considered. Simulation and experimental results validated the drive configurations in this dissertation. An integrated AC/AC converter was developed for 2-phase motor drives. Additionally, the proposed integrated AC/AC converter was systematically compared with commonly used topologies including AC/DC/AC converter and matrix converters, in terms of the output voltage/current capability, total harmonics distortion (THD), and system cost. Furthermore, closed-loop speed controllers were developed for the three topologies, and the maximum operating range and output phase currents were investigated. The proposed integrated AC/AC converter with a single-phase input and a 2-phase output reduced the switch count to six and resulting in minimized system cost and size for low power applications. In contrast, AC/DC/AC pulse width modulation (PWM) converters contained twelve active power semiconductor switches and a common DC link. Furthermore, a modulation scheme and filters for the proposed converter were developed and modeled in detail. For the significantly increased bearing current caused by the transition from Si devices to WBG devices, advanced modeling and analysis approach was proposed by using coupled field-circuit electromagnetic finite element analysis (FEA) to model bearing voltage and current in electric machines, which took into account the influence of distributed winding conductors and frequency-dependent winding RL parameters. Possible bearing current issues in axial-flux machines, and possibilities of computation time reduction, were also discussed. Two experimental validation approaches were proposed: the time-domain analysis approach to accurately capture the time transient, the stationary testing approach to measure bearing capacitance without complex control development or loading condition limitations. In addition, two types of motors were employed for experimental validation: an inside-out N-type PMSM was used for rotating testing and stationary testing, and an N-type BLDC was used for stationary testing. Possible solutions for the increased CMV and bearing currents caused by the implementation of WGB devices were discussed and developed in simulation validation, including multi-carrier SPWM modulation and H-8 converter topology

Survey of applications of WBG devices in power electronics

Master of ScienceDepartment of Electrical and Computer EngineeringBehrooz MirafzalWide bandgap devices have gained increasing attention in the market of power electronics for their ability to perform even in harsh environments. The high voltage blocking and high temperature withstanding capabilities make them outperform existing Silicon devices. They are expected to find places in future traction systems, electric vehicles, LED lightning and renewable energy engineering systems. In spite of several other advantages later mentioned in this paper, WBG devices also face a few challenges which need to be addressed before they can be applied in large scale in industries. Electromagnetic interference and new requirements in packaging methods are some of the challenges being faced by WBG devices. After the commercialization of these devices, many experiments are being carried out to understand and validate their abilities and drawbacks. This paper summarizes the experimental results of various applications of mainly Silicon Carbide (SiC) and Gallium Nitride (GaN) power devices and also includes a section explaining the current challenges for their employment and improvements being made to overcome them

High Frequency Injection Sensorless Control for a Permanent Magnet Synchronous Machine Driven by an FPGA Controlled SiC Inverter

As motor drive inverters continue to employ Silicon Carbide (SiC) and Gallium Nitride (GaN) devices for power density improvements, sensorless motor control strategies can be developed with field-programmable gate arrays (FPGA) to take advantage of high inverter switching frequencies. Through the FPGA’s parallel processing capabilities, a high control bandwidth sensorless control algorithm can be employed. Sensorless motor control offers cost reductions through the elimination of mechanical position sensors or more reliable electric drive systems by providing additional position and speed information of the electric motor. Back electromotive force (EMF) estimation or model-based methods used for motor control provide precise sensorless control at high speeds; however, they are unreliable at low speeds. High frequency injection (HFI) sensorless control demonstrates an improvement at low speeds through magnetic saliency tracking. In this work, a sinusoidal and square-wave high frequency injection sensorless control method is utilized to examine the impact an interior permanent magnet synchronous machine’s (IPMSM) fundamental frequency, injection frequency, and switching frequency have on the audible noise spectrum and electrical angle estimation. The audible noise and electrical angle estimation are evaluated at different injection voltages, injection frequencies, switching frequencies, and rotor speeds. Furthermore, a proposed strategy for selecting the proper injection frequency, injection voltage, and switching frequency is given to minimize the electrical angle estimation error

Implementation and Analysis of Direct Torque Control for Permanent Magnet Synchronous Motor Using Gallium Nitride based Inverter

Permanent magnet synchronous machines (PMSMs) attract considerable attention in various industrial applications, such as electric and hybrid electric vehicles, due to their high efficiency and high-power density. In this thesis, the mathematical model of PMSM and two popular control strategies, field-oriented control (FOC) and direct torque control (DTC), are analyzed and compared. The results demonstrated that the DTC has better dynamic response in comparison to FOC. Moreover, DTC can eliminate the use of position sensor, which will save the cost of the PMSM drive system. Therefore, this thesis focuses on the design and implementation of high-performance DTC for PMSMs with a Gallium Nitride (GaN) based high switching frequency motor drive. First, the characteristics and operation principles of a PMSM are introduced. Then, the mathematical models of a PMSM under different coordinate systems are investigated. Consequently, a PMSM model is developed based on the dq rotating reference frame and implemented in the MATLAB/Simulink for validation. Two advanced PMSM control strategies, FOC and DTC, are investigated and compared in terms of control performance through comprehensive simulation studies and the results demonstrate that DTC has better dynamic performance. Conventional DTC contributes to higher torque ripple in the PMSM due to the limited switching frequency in a conventional semiconductor-based motor drive, which inevitably deteriorates the drive performance. Therefore, this thesis aims to reduce the torque ripple in the DTC based PMSM drive by using the new generation wide bandgap switching devices. More specifically, DTC is improved by using the optimized space vector pulse width modulation strategy and a higher switching frequency contributed by the GaN based motor drive. Finally, the proposed DTC-SVM based PMSM control strategy is implemented on the digital signal processor (DSP) and evaluated on the laboratory GaN based PMSM drive. Both the simulation and experimental results show that the proposed improvement in the DTC can further improve the PMSM drive performance

Energy-efficient and Power-dense DC-DC Converters in Data Center and Electric Vehicle Applications Using Wide Bandgap Devices

The ever increasing demands in the energy conversion market propel power converters towards high efficiency and high power density. With fast development of data processing capability in the data center, the server will include more processors, memories, chipsets and hard drives than ever, which requires more efficient and compact power converters. Meanwhile, the energy-efficient and power-dense converters for the electric vehicle also result in longer driving range as well as more passengers and cargo capacities. DC-DC converters are indispensable power stages for both applications. In order to address the efficiency and density requirements of the DC-DC converters in these applications, several related research topics are discussed in this dissertation. For the DC-DC converter in the data center application, a LLC resonant converter based on the newly emerged GaN devices is developed to improve the efficiency over the traditional Si-based converter. The relationship between the critical device parameters and converter loss is established. A new perspective of extra winding loss due to the asymmetrical primary and secondary side current in LLC resonant converter is proposed. The extra winding loss is related to the critical device parameters as well. The GaN device benefits on device loss and transformer winding loss is analyzed. An improved LLC resonant converter design method considering the device loss and transformer winding loss is proposed. For the DC-DC converter in the electric vehicle application, an integrated DC-DC converter that combines the on-board charger DC-DC converter and drivetrain DC-DC converter is developed. The integrated DC-DC converter is considered to operate in different modes. The existing dual active bridge (DAB) DC-DC converter originally designed for the charger is proposed to operate in the drivetrain mode to improve the efficiency at the light load and high voltage step-up ratio conditions of the traditional drivetrain DC-DC converter. Design method and loss model are proposed for the integrated converter in the drivetrain mode. A scaled-down integrated DC-DC converter prototype is developed to verify the design and loss model

Reliability-driven assessment of GaN HEMTs and Si IGBTs in 3L-ANPC PV inverters

In this paper, thermal loading of the state-of-the-art GaN HEMTs and traditional Si IGBTs in 3L-ANPC PV inverters is presented considering real-field long-term mission profiles (i.e., ambient temperature and solar irradiance). A comparison of Si IGBT against GaN HEMT with three different possibilities: 1) with TIM at 10 kHz, 2) without TIM at 10 kHz, and 3) with TIM at 300 kHz has been performed. The assessment results indicate lower thermal stress with GaN HEMT devices at 10 kHz in comparison to Si IGBT. At high switching frequencies, the results show significant system level cost savings can be achieved without compromise of operating efficiency with GaN HEMTs. Both simulations and experimental tests are provided to demonstrate the thermal loading analysis approach. More important, the proposed analysis and comparison approach can be used for lifetime and reliability analysis of wide-bandgap devices

Analysis and optimization of the hardware design of a sic mosfet based power converter with sic schottky diodes utilizing a split output topology

In recent years, the use of power electronic devices for energy conversion with semiconductors such as silicon carbide (SiC) or gallium nitride (GaN) are replacing silicon due to their high thermal conductivity, efficiency, resistance, and the possibility of smaller and thinner designs. For this reason, in order to evaluate the improvement potential of these systems, it is beneficial to realize experimental setups that emulate real operating conditions in order to verify the correct performance of these systems. In this context and based on the previous work done by Giorgio Ferrara, this thesis focuses on the analysis and identification of improvements of a SiC MOSFET-based power electronic converter with the aim of suggesting and studying different solutions that ensure a high-performance operation that allows its correct implementation in motor traction and grid-connected applications. During the thesis work, it is carried out an in-depth analysis of the voltage peaks between drain and source originated by the fast switching of the MOSFET to evaluate the use of Snubber capacitors and it is made a new hardware design of the gate driver board using isolated gate drivers to improve the dynamic behaviour in the switching transients of the SiC transistors and provide safety and robustness to the system. Finally, maintaining the original design of the converter, it implements the split output topology to evaluate possible solutions to the problems of electromagnetic interference (EMI) and the crosstalk effect that occurs with high frequency switchingNegli ultimi anni, l'uso di dispositivi elettronici di potenza per la conversione dell'energia con semiconduttori come il carburo di silicio (SiC) o il nitruro di gallio (GaN) sta sostituendo il silicio grazie alla sua elevata conducibilità termica, all'efficienza, alla resistenza e alla possibilità di realizzare disegni più piccoli e sottili. Per questo motivo, al fine di valutare il potenziale di miglioramento di questi sistemi, è utile realizzare set-up sperimentali che emulino le condizioni operative reali, in modo da poter eseguire diversi test per verificare il corretto comportamento di questi sistemi. In tale contesto e a partire dal precedente lavoro effettuato per Giorgio Ferrara, la presente tesi si concentra nell' analisi e nidentificazione di miglioramenti di un convertitore di potenza DC-AC a commutazione, al fine di proporre e studiare diverse soluzioni che garantiscano le elevate prestazioni che assicurano la sua corretta implementazione in applicazioni di trazione a motore e di connessione alla rete. Durante il lavoro di tesi, si analizza in dettaglio il fenomeno di picchi di tensione tra drain e source causato per la commutazione veloce del MOSFET e si valuta l'utilizzo di condensatori snubber; in più si realizza un nuovo disegno hardware della board di gate driver utilizzando gate driver isolati per migliorare il comportamento dinamico nei transitori di commutazione dei transistor SiC e per fornire sicurezza e robustezza al sistema. Per finire, mantenendo il disegno originale del convertitore, implementa la topologia di uscita Split Output per valutare possibili soluzioni ai problemi di interferenza elettromagnetica (EMI) e all'effetto diafonia che si produce con la commutazione ad alta frequenzaObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura::9.5 - Augmentar la investigació científica i millorar la capacitat tecnològica dels sectors industrials de tots els països, en particular els països en desenvolupament, entre d’altres maneres fomentant la innovació i augmentant substancialment, d’aquí al 2030, el nombre de persones que treballen en el camp de la investigació i el desenvolupa­ment per cada milió d’habitants, així com la despesa en investigació i desenvolupament dels sectors públic i priva