An Insight into the Voltage Rising Behavior during Turn-off Process of Series Connected SiC MOSFETs on Circuit Level

Current commercial available SiC MOSFET can hardly meet the requirement of high-voltage electrical application. Connecting SiC MOSFETs in series is a feasible solution. In order to utilize series connected SiC MOSFETs better, a comprehensive understanding of its switching process is of great necessity, especially turn-off process when huge different voltage sharing may occur. This paper focus on two factors, the nonlinearity of SiC MOSFET junction capacitance C_j and the existence of freewheeling diode junction capacitance C_f. A circuit analysis of series connected SiC MOSFETs is proposed. This paper analyzes the turn-off process of series connected SiC MOSFETs qualitatively and mathematically, and the expressions of key parameters, such as dvds/dt during turn-off process, are derived. The characteristics of series connected SiC MOSFETs during turn-off process are revealed. Finally, the accuracy of the analysis is verified by experimental results.