Active Control and Gate-Driver Design for Voltage Balancing of Both MOSFETs and Body-Diodes in Series-Connected SiC MOSFETs

Series-connected SiC MOSFETs under ac load current requires the voltage balancing for both MOSFETs and body-diodes. The passive snubber solution improves the voltage sharing of both MOSFETs and body-diodes but significantly increases the switching losses. Although the existing active voltage balancing (AVB) methods minimize the extra switching losses, they can only achieve the voltage adjustment of MOSFETs. To achieve the active voltage adjustment for both MOSFETs and body-diodes, this paper proposes a new AVB method for two series-connected SiC MOSFETs: after the turn-off transient, an extra short-pulse gate signal is applied on one device to adjust the channel resistance and control the voltage sharing. This paper first presents the detailed impact and implementation of the short-pulse gate signal on the voltage sharing under ac load current. The closed-loop control of short-pulse width and its integration with gate driver design is then introduced. To verify the proposed AVB approach and the designed gate driver, experiments with two series-connected 10 kV SiC MOSFETs under different conditions are conducted and presented at the end of the paper.