Date of Graduation

8-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Electrical Engineering

Advisor/Mentor

Mantooth, H. Alan

Committee Member

Balda, Juan C.

Second Committee Member

Zhao, Yue

Third Committee Member

Li, Qinghua

Keywords

Active gate driver; EMI; MOSFET; Optimization; Silicon carbide; Trajectory model

Abstract

The penetration of silicon carbide (SiC) semiconductor devices is increasing in the power industry due to their lower parasitics, higher blocking voltage, and higher thermal conductivity over their silicon (Si) counterparts. Applications of high voltage SiC power devices, generally 10 kV or higher, can significantly reduce the amount of the cascaded levels of converters in the distributed system, simplify the system by reducing the number of the semiconductor devices, and increase the system reliability.

However, the gate drivers for high voltage SiC devices are not available on the market. Also, the characteristics of the third generation 10 kV SiC MOSFETs with XHV-6 package which are developed by CREE are approaching those of an ideal switch with high dv/dt and di/dt. The fast switching speed of SiC devices introduces challenges for the application since electromagnetic interference (EMI) noise and overshoot voltage can be serious. Also, the insulation should be carefully designed to prevent partial discharge.

To address the aforementioned issues, this work investigates the switching behaviors of SiC power MOSFETs with mathematic models and the formation of EMI noise in a power converter. Based on the theoretical analysis, a model-based switching trajectory optimizing three-level active gate driver (AGD) is proposed. The proposed AGD has five operation modes, i.e., faster/normal/slower for the turn-on process and slower/normal for the turn-off process. The availability of multiple operation modes offers an extra degree of freedom to improve the switching performance for a particular application and enables it to be more versatile. The proposed AGD can provide higher switching speed adjustment resolution than the other AGDs, and this feature will allow the proposed AGD to fine tune the switching speed of SiC power devices. In addition, a novel model-based trajectory optimization strategy is proposed to determine the optimal gate driver output voltage by trading the EMI noise against the switching energy losses. For the 10 kV SiC power MOSFET, the detailed design considerations of the proposed AGD are demonstrated in this dissertation. The functionalities of the 3-L AGD are validated through the double pulse tests results with 1.2 kV and 10 kV SiC power MOSFETs.

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