(Invited) Emerging Role of Silicon Carbide and Gallium Nitride Based Power Electronics in Power and Transportation Sectors

Free fuel-based energy sources (solar and wind) are pointing towards a future in which sustainable energy is affordable, abundant and deployed with high energy efficiency. Driven by advancements in the technology of lithium batteries and the availability of low-cost sustainable clean electric power, the electrification of transportation is going through fundamental disruptive transformation. Without any doubt, both power and transportation sectors will provide phenomenal growth of power electronics in the 21st century. Recently, both SiC and GaN are drawing the attention as potential replacement of Si-based power electronics. These may open some new markets where Si based power electronics cannot function either due to power or temperature limitations. In this paper we have identified the WBG based key power electronics products that should be focused to see their high growth

Degradation modeling and degradation-aware control of power electronic systems

The power electronics market is valued at $23.25 billion in 2019 and is projected to reach$ 36.64 billion by 2027. Power electronic systems (PES) have been extensively used in a wide range of critical applications, including automotive, renewable energy, industrial variable-frequency drive, etc. Thus, the PESs\u27 reliability and robustness are immensely important for the smooth operation of mission-critical applications. Power semiconductor switches are one of the most vulnerable components in the PES. The vulnerability of these switches impacts the reliability and robustness of the PES. Thus, switch-health monitoring and prognosis are critical for avoiding unexpected shutdowns and preventing catastrophic failures. The importance of the prognosis study increases dramatically with the growing popularity of the next-generation power semiconductor switches, wide bandgap switches. These switches show immense promise in the high-power high-frequency operations due to their higher breakdown voltage and lower switch loss. But their wide adaptation is limited by the inadequate reliability study. A thorough prognosis study comprising switch degradation modeling, remaining useful life (RUL) estimation, and degradation-aware controller development, is important to enhance the PESs\u27 robustness, especially with wide bandgap switches. In this dissertation, three studies are conducted to achieve these objectives- 1) Insulated Gate Bipolar Transistor (IGBT) degradation modeling and RUL estimation, 2) cascode Gallium Nitride (GaN) Field-Effect Transistor (FET) degradation modeling and RUL estimation, and 3) Degradation-aware controller design for a PES, solid-state transformer (SST). The first two studies have addressed the significant variation in RUL estimation and proposed degradation identification methods for IGBT and cascode GaN FET. In the third study, a system-level integration of the switch degradation model is implemented in the SST. The insight into the switch\u27s degradation pattern from the first two studies is integrated into developing a degradation-aware controller for the SST. State-of-the-art controllers do not consider the switch degradation that results in premature system failure. The proposed low-complexity degradation-aware and adaptive SST controller ensures optimal degradation-aware power transfer and robust operation over the lifetime

Smart Power Devices and ICs Using GaAs and Wide and Extreme Bandgap Semiconductors

We evaluate and compare the performance and potential of GaAs and of wide and extreme bandgap semiconductors (SiC, GaN, Ga2O3, diamond), relative to silicon, for power electronics applications. We examine their device structures and associated materials/process technologies and selectively review the recent experimental demonstrations of high voltage power devices and IC structures of these semiconductors. We discuss the technical obstacles that still need to be addressed and overcome before large-scale commercialization commences

Overview of Power Electronic Switches: A Summary of the Past, State-of-the-Art and Illumination of the Future

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Wide-band Gap Devices for DC Breaker Applications

With the increasing interest in wide-band gap devices, their potential benefits in power applications have been studied and explored with numerous studies conducted for both SiC and GaN devices. This thesis investigates the use of wide-band gap devices as the switching element in a semiconductor DC breaker. It involves the design of an efficient semiconductor DC breaker, its simulation in SPICE, construction of a hardware prototype and the comparative study of SiC and Si versions of the aforementioned breaker. The results obtained from the experiments conducted in the process of concluding this thesis show that the SiC version of the breaker is a superior option for a semiconductor DC breaker

Power electronics based on wide-bandgap semiconductors: opportunities and challenges

The expansion of the electric vehicle market is driving the request for efficient and reliable power electronic systems for electric energy conversion and processing. The efficiency, size, and cost of a power system is strongly related to the performance of power semiconductor devices, where massive industrial investments and intense research efforts are being devoted to new wide bandgap (WBG) semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN). The electrical and thermal properties of SiC and GaN enable the fabrication of semiconductor power devices with performance well beyond the limits of silicon. However, a massive migration of the power electronics industry towards WBG materials can be obtained only once the corresponding fabrication technology reaches a sufficient maturity and a competitive cost. In this paper, we present a perspective of power electronics based on WBG semiconductors, from fundamental material characteristics of SiC and GaN to their potential impacts on the power semiconductor device market. Some application cases are also presented, with specific benchmarks against a corresponding implementation realized with silicon devices, focusing on both achievable performance and system cost

Design and construction of a half-bridge using wide-bandgap transistors

A continuously increasing demand of electric power makes energy efficiency imperative in modern technology. The transistor is considered as the fundamental element of modern electronic products

Design and Advanced Model Predictive Control of Wide Bandgap Based Power Converters

The field of power electronics (PE) is experiencing a revolution by harnessing the superior technical characteristics of wide-band gap (WBG) materials, namely Silicone Carbide (SiC) and Gallium Nitride (GaN). Semiconductor devices devised using WBG materials enable high temperature operation at reduced footprint, offer higher blocking voltages, and operate at much higher switching frequencies compared to conventional Silicon (Si) based counterpart. These characteristics are highly desirable as they allow converter designs for challenging applications such as more-electric-aircraft (MEA), electric vehicle (EV) power train, and the like. This dissertation presents designs of a WBG based power converters for a 1 MW, 1 MHz ultra-fast offboard EV charger, and 250 kW integrated modular motor drive (IMMD) for a MEA application. The goal of these designs is to demonstrate the superior power density and efficiency that are achievable by leveraging the power of SiC and GaN semiconductors. Ultra-fast EV charging is expected to alleviate the challenge of range anxiety , which is currently hindering the mass adoption of EVs in automotive market. The power converter design presented in the dissertation utilizes SiC MOSFETs embedded in a topology that is a modification of the conventional three-level (3L) active neutral-point clamped (ANPC) converter. A novel phase-shifted modulation scheme presented alongside the design allows converter operation at switching frequency of 1 MHz, thereby miniaturizing the grid-side filter to enhance the power density. IMMDs combine the power electronic drive and the electric machine into a single unit, and thus is an efficient solution to realize the electrification of aircraft. The IMMD design presented in the dissertation uses GaN devices embedded in a stacked modular full-bridge converter topology to individually drive each of the motor coils. Various issues and solutions, pertaining to paralleling of GaN devices to meet the high current requirements are also addressed in the thesis. Experimental prototypes of the SiC ultra-fast EV charger and GaN IMMD were built, and the results confirm the efficacy of the proposed designs. Model predictive control (MPC) is a nonlinear control technique that has been widely investigated for various power electronic applications in the past decade. MPC exploits the discrete nature of power converters to make control decisions using a cost function. The controller offers various advantages over, e.g., linear PI controllers in terms of fast dynamic response, identical performance at a reduced switching frequency, and ease of applicability to MIMO applications. This dissertation also investigates MPC for key power electronic applications, such as, grid-tied VSC with an LCL filter and multilevel VSI with an LC filter. By implementing high performance MPC controllers on WBG based power converters, it is possible to formulate designs capable of fast dynamic tracking, high power operation at reduced THD, and increased power density

High Efficiency Power Converters for Vehicular Applications

The use of power electronics in the electrical propulsion systems leads to the optimal and efficient utilization of the traction motors and the energy sources (batteries and/or fuel cells) through the recourse to suitable power converters and their proper control. Power electronics is also used for implementing the multiple conversions of the energy delivered by the sources to feed the various loads, most of them requiring different waveforms of voltage (ac or dc) and/or different levels of voltage. This work focuses on the solutions aimed at improving the efficiency of power converters for vehicular applications, which is of great importance because of the limited amount of energy that can be stored in the electric vehicles. The study takes into consideration both the traction applications and the battery charging applications whether it is done by conductive means or by wireless power transfer (WPT) systems. The improvement in traction drive efficiency results in an increment of the drivetrain efficiency of the vehicle, leading to an extension in the driving range, while the employment of efficient power converters is required to charge batteries with increasingly large capacity. The losses of power devices are even more significant when they operate at high frequencies to compact the size of the filter elements and/or the transformers. The losses of power devices can be minimized by making the commutation soft or by replacing the conventional devices with the new generation devices based on wide bandgap (WBG) semiconductor materials. In this work, the properties of the WBG semiconductor materials are illustrated and the operation of the devices based on these materials are analyzed to grasp better their characteristics and performance. The losses of individual devices (i.e. diode, IGBT, MOSFET) as well as the operation of power converters for various applications are examined in detail. To evaluate the performance of the SiC devices in electric vehicle applications, an AC traction drive for the propulsion of a typical compact C-class electric car has been considered. Two versions of the inverter have been investigated, one built up with conventional Si IGBTs and the other one with SiC MOSFETs, and the losses in the semiconductor devices of the two versions have been found along the standard New European Driving Cycle (NEDC). By comparing the results, it is emerged that the usage of the SiC MOSFETs reduces the losses in the traction inverter of about 5%, yielding an equal increase in the car range. To complete the study, calculation of the efficiency has been extended to the whole traction drive, including the traction motor and the gear. Afterwards, a power factor correction (PFC) circuit, which is commonly used to mitigate the distortion in line current, has been studied. The study is started by considering the basic and the interleaved PFC configurations and by defining their circuit parameters. After selecting the interleaved configuration, the magnitude of voltages and currents in the PFC rectifier has been determined and the values obtained have been verified by a power circuit simulation software. The digital signal processing (DSP) has been also studied as it is used for the control operation of the PFC. At last, a prototype of PFC rectifier with interleaved configuration is designed. The design process and the specification of the components are described in brief. A prototype of synchronous rectifier (SR) is designed for the output stage of a WPT system. With respect to conventional rectifiers, in SRs the diodes are replaced by MOSFETs with their antiparallel diodes. MOSFETs are bidirectional devices that conduct with a low voltage drop. During the dead time, the diodes in antiparallel to the MOSFETs are conducting. At the end of dead-time, signals are applied at the MOSFET gates that make conducting all along the remaining period, thus reducing the conduction losses. The dead-time length is optimized by using fast switching devices based on SiC semiconductor materials. The prototype is designed and tested at the line frequency. The experimental results obtained from the prototype corroborate both the analytical results and the simulation results. As SR exhibits is working with high efficiency at the line frequency, it is expected that at the higher operating frequencies of the WPT systems, the performance of SR will be even better. A DC-DC isolated power converters used to setup the battery charger through wire system are studied. Two topologies of DC-DC converters, i.e. Dual Active Bridge (DAB) and Single Active Bridge (SAB) converters, are considered. For both the topologies operation are described at steady state. For SAB converter, two possible modes of operation are examined: discontinuous current conduction (DCM) and continuous current conduction (CCM). Soft-switching operation of both SAB and DAB converters, obtained by the insertion of auxiliary capacitors, is analyzed. Moreover, the soft-switching operating zone for the two converters are found as a function of the their output voltages and currents. Finally, the comparative analysis of soft-switching operation of SAB versus DAB converter is presented. The thesis work has been carried out at the Laboratory of “Electric Systems for Automation and Automotive” headed by Prof. Giuseppe Buja. The laboratory belongs to the Department of Industrial Engineering of the University of Padova, Italy

Experimental Evaluation of Medium-Voltage Cascode Gallium Nitride (GaN) Devices for Bidirectional DC–DC Converters

As renewable energy sources, such as photovoltaic (PV) cells and wind turbines, are rapidly implemented in DC microgrids, energy storage systems play an increasingly significant role in ensuring uninterrupted power supply and in supporting the reliability and stability of microgrid operations. Power electronics, especially bidirectional DC–DC converters, are essential parts in distributed energy storage and alternative energy systems because of their grid synchronization, DC power management, and bidirectional power flow capabilities. While there is increasing demand for more efficient, compact, and reliable power converters in numerous applications, most existing power converters are hindered by traditional silicon (Si) based semiconductors, which are reaching their theoretical and material limits as there is an insignificant possibility for further improvements. Wide bandgap (WBG) semiconductors, such as gallium nitride (GaN) and silicon carbide (SiC), exhibit superior physical properties and demonstrate great potential for replacing conventional Si semiconductors with WBG technology, pushing the boundaries of power devices to handle higher switching frequencies, output power levels, blocking voltages, and operating temperatures. However, tradeoffs in switching performance and converter efficiency when substituting GaN devices for Si and SiC counterparts are not well defined, especially in a cascode configuration. Additional research with further detailed investigation and analysis is necessitated for medium-voltage GaN devices in power converter applications. Therefore, the objective of this research is to experimentally investigate the impact of emerging 650/900 V cascode GaN switching devices on bidirectional DC–DC converters that are suitable for energy storage and distributed renewable energy systems. Dynamic characteristics of Si, SiC, and cascode GaN power devices are examined through the double-pulse test (DPT) at different gate resistance values, device currents, and DC-bus voltages. Furthermore, the switching behavior and energy loss as well as the rate of voltage and current changes over the time are studied and analyzed at different operating conditions. A 500 W experimental converter prototype is designed and implemented to validate the benefits of cascode GaN devices on the converter operation and performance. Comprehensive analysis of the power losses and efficiency improvements for Si- based, SiC-based, and GaN-based converters are performed and evaluated as the switching frequency, working temperature, and output power level are increased. The experimental results reveal a significant improvement in switching performance and energy efficiency from cascode GaN power devices used in the bidirectional converters