Abstract

In recent years, wide-bandgap devices (WBG) such as silicon carbide (SiC) and gallium nitride (GaN) transistors have drawn significant research attention in power conversion applications where higher efficiency, higher power density and lower cost are required, for example, in electric vehicle (EV) applications. Owing to its better figures of merit on on-resistance, switching speed and junction temperature, enhancement-mode GaN high electron mobility transistors (HEMTs) are able to be operated with switching frequency up to the megahertz range, through which the size of passive components in the power converters can be significantly reduced. Consequently, the power converter’s integration level and power density can be increased.
In GaN-based power converters, the switching energy loss increases naturally along with the switching frequency, which is the dominant loss component. Consequently, it is always one of the top priority performances to be considered in research and development activities. For device manufacturers, with access to internal materials and dimensional parameters, physics-based device models are usually used. Although these models can reveal detailed characteristics of the devices, they are not accessible to the public and can be very time-consuming to develop. Analytical models, that can emulate the transistor’s dynamic behaviour and predict the switching energy loss without consuming too much computing resources, are always an essential tool to help provide guidelines to engineers for circuit design and performance optimization purposes. This thesis develops a computationally inexpensive and straightforward switching transient model which proves to be more accurate than conventional model through simulation and experiments.
Currently, in the commercial market, there are only a few mature designs of GaN three-phase inverter products, and most of them are costly. This unavoidable phenomenon is led by the fact that the gate driver and power loop design for GaN is demanding. Some companies such as EPC, Navitas and Power Integrations are committed to monolithic-integrated gate drivers, but they are complex and expensive. Thus, this thesis also aims to design a GaN-based three-phase inverter with low cost and low complexity in the gate drive circuit. In addition, to achieve high performance GaN-based inverter, parasitic components in the power loop have to be minimized. In this thesis study, parasitic parameters of the power loop are extracted through Ansys Q3D simulation and then validated through experimental test results. With accurate parasitic parameters, the layout of the PCBs is improved to achieve better inverter performance.