The emergence of wide-bandgap-based (WBG) devices, such as silicon carbide (SiC) and gallium nitride (GaN), have unveiled unprecedented opportunities, enabling the realization of superior power conversion systems. Among the potential areas of advancement are medium-voltage (MV) and high-voltage (HV) applications, due to the growing demand for high-power-density and high-efficiency power electronics converters. These advancements have propelled a wide adoption of electric vehicles (EV), which in the future will require great improvements in the charging time of these vehicles. Thereby, this thesis attempts to address such a challenge and bring about technological improvements, enabling faster, more efficient, and more effective ways of charging an electric vehicle through the application of MV 3.3 kV SiC MOSFETs. The current fast-charging solution involves heavy and bulky MV-LV transformers, which add installation complexity for EV charging stations. However, this thesis presents an alternative power-delivery solution utilizing an MV dual-active-bridge (DAB) converter. The proposed architecture is designed to directly interface with the MV grid for high-power, fast-charging capabilities while eliminating the need for an installation of the MV-LV transformer. The MV DAB converter utilizes 3.3 kV SiC MOSFETs to realize the next 800 V EV charging system, along with an extended zero-voltage-switching (ZVS) scheme, in order to provide an efficient charging strategy across a wide range of battery voltage levels. Lastly, a detailed design comparison analysis of an MV Flyback converter, targeted for the auxiliary power supply for the proposed MV EV charging architecture, is presented. / The field of power electronics, which controls and manages the conversion of electrical energy, is an important topic of discussion, as new technologies like electric vehicles (EV) are quickly emerging and disrupting the current status-quo of vehicle-choice. In order to promote timely and extensive adoption of such an enabling EV technology, it is critical to understand the current challenges involving EV charging stations and seek out opportunities to engender future innovations. Indeed, wide-bandgap (WBG) devices, such as silicon carbide (SiC) and gallium nitride (GaN), have unveiled unprecedented opportunities in enabling the realization of superior power conversion systems. Thus, utilizing these WGB devices in EV charging applications can bring about improved design and development of EV fast chargers that are faster-charging, more efficient, and more effective. Hence, this thesis presents an opportunity in EV charging station applications with the utilization of medium-voltage SiC MOSFETs. Because the current fast-charging solution involves a heavy and bulky transformer, it adds installation complexity for EV charging stations. However, this thesis presents an alternative power-delivery solution that could potentially provide an efficient and fast-charging mechanism of EVs while reducing the size of EV chargers. All things considered, this thesis provides in-depth evaluation-studies of medium-voltage 3.3 kV SiC MOSFET-based power converters, targeted for future fast EV charging applications. The development and design of the hardware prototype is presented in this thesis, along with testing and verification of experimental results.

The trend towards more and all-electric apparatuses and more electrification will lead to higher electrical demand. Increases in electrical power demand can be provided by either higher currents or higher voltages. Due to "weight" and "voltage" drop, a raise in the current is not preferred; so, "higher voltages" are being considered. Another trend is to reduce the size and weight of apparatuses. Combined, these two trends result in the high voltage, high power density concept. It is expected that by 2030, 80% of all electric power will flow through "power electronics systems". In regards to the high voltage, high power density concept described above, "wide bandgap (WBG) power modules" made from materials such as "SiC and GaN (and, soon, Ga2O3 and diamond)", which can endure "higher voltages" and "currents" rather than "Si-based modules", are considered to be the most promising solution to reducing the size and weight of "power conversion systems". In addition to the trend towards higher "blocking voltage", volume reduction has been targeted for WBG devices. The blocking voltage is the breakdown voltage capability of the device, and volume reduction translates into power density increase. This leads to extremely high electric field stress, E, of extremely nonuniform type within the module, leading to a higher possibility of "partial discharge (PD)" and, in turn, insulation degradation and, eventually, breakdown of the module. Unless the discussed high E issue is satisfactorily addressed and solved, realizing next-generation high power density WBG power modules that can properly operate will not be possible. Contributions and innovations of this Ph.D. work are as follows. i) Novel electric field grading techniques including (a) various geometrical techniques, (b) applying "nonlinear field-dependent conductivity (FDC) materials" to high E regions, and (c) combination of (a) and (b), are developed; ii) A criterion for the electric stress intensity based upon accurate dimensions of a power device package and its "PD measurement" is presented; iii) Guidelines for the electrical insulation design of next-generation high voltage (up to 30 kV), high power density "WBG power modules" as both the "one-minute insulation" and PD tests according to the standard IEC 61287-1 are introduced; iv) Influence of temperature up to 250°C and frequency up to 1 MHz on E distribution and electric field grading methods mentioned in i) is studied; and v) A coupled thermal and electrical (electrothermal) model is developed to obtain thermal distribution within the module precisely. All models and simulations are developed and carried out in COMSOL Multiphysics. / Doctor of Philosophy / In power engineering, power conversion term means converting electric energy from one form to another such as converting between AC and DC, changing the magnitude or frequency of AC or DC voltage or current, or some combination of these. The main components of a power electronic conversion system are power semiconductor devices acted as switches. A power module provides the physical containment and package for several power semiconductor devices. There is a trend towards the manufacturing of electrification apparatuses with higher power density, which means handling higher power per unit volume, leading to less weight and size of apparatuses for a given power. This is the case for power modules as well. Conventional "silicon (Si)-based semiconductor technology" cannot handle the power levels and switching frequencies required by "next-generation" utility applications. In this regard, "wide bandgap (WBG) semiconductor materials", such as "silicon carbide (SiC)"," gallium nitride (GaN)", and, soon, "gallium oxide" and "diamond" are capable of higher switching frequencies and higher voltages, while providing for lower switching losses, better thermal conductivities, and the ability to withstand higher operating temperatures. Regarding the high power density concept mentioned above, the challenge here, now and in the future, is to design compact WBG-based modules. To this end, the extremely nonuniform high electric field stress within the power module caused by the aforementioned trend and emerging WBG semiconductor switches should be graded and mitigated to prevent partial discharges that can eventually lead to breakdown of the module. In this Ph.D. work, new electric field grading methods including various geometrical techniques combined with applying nonlinear field-dependent conductivity (FDC) materials to high field regions are introduced and developed through simulation results obtained from the models developed in this thesis.