Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Electrical Engineering

Major Professor

Hua Bai

Committee Members

Hua (Kevin) Bai, Fei (Fred) Wang, Leon M. Tolbert, Yunting Liu


This dissertation focuses on hybrid switches, onboard chargers (OBCs) and auxiliary power modules (APMs). Firstly, a hybrid switch module paralleling Si with Gallium Nitride (GaN) device is proposed to replace the paralleled pure GaN devices. The power loop and gate-drive loop transients are thoroughly analyzed to guide the hardware design. A 400V/80A full bridges module was designed and used to verify the correctness of the theoretical analysis. Test results confirmed the idea. Also, the guideline of Si devices selection is developed for future hybrid switches designs. Secondly, a high power 12V/6kW APM is developed following a generalized hybrid switch methodology. A two-stage topology consisting of both Si and WBG devices is proposed and developed to make the most of both types of devices. Also, this dissertation proposed the corresponding control method to secure zero voltage switching (ZVS) operation of both stages. A DC bias current could be a potential risk for such applications. Thus, a simple and effective bias current detection method is built and deployed. This dissertation also proposed a bi-directional APM operation to pre-charge the HV side. All the proposed ideas are verified on the developed hardware, which also successfully delivers 12V/6kW. Lastly, a novel three-port DC-DC converter with a three-winding transformer is proposed to integrate APM with OBC both electrically and magnetically to save cost and size. The proposed converter with power decoupling control allows the power to flow freely among three ports. Due to the complexity of the proposed converter, a comprehensive model is developed to predict the whole system's behavior, including ZVS current, switching current, reactive power, etc. The APM mode of the integrated charger is also investigated to extend the input and output voltage range. By adding a selecting switch, the existing topology can be easily extended for a universal APM to cover both 400 V and 800 V EV systems. A simple but effective optimization and control method is also proposed to secure ZVS and minimize the switching current for full voltage and power range.

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