Active Voltage Balancing of Series-Connected SiC MOSFETs During Body-Diode Turn-Off Using an Active Gate Driver

The series connection of fast-switching SiC mosfets presents a promising approach to enhance the efficiency, compactness, and simplicity of medium voltage (MV) power converters. However, managing voltage imbalances during the turn-offof mosfets and their body diodes introduces significant challenges. While existing literature covers passive and active voltage balancing strategies for switch turn-off (e.g., mosfets/IGBTs), the issue of uneven voltage distribution during body diode turn-off remains largely unexplored. This gap limits the widespread adoption of series-connected devices in MV power converters, as achieving reliable performance with minimal additional components and low switching losses remains difficult. This article presents an active voltage balancing technique for handling body diode turn-off events by regulating the gate charge of parallel mosfets during voltage rise transients in the closed-loop using active gate drivers (AGD). This approach ensures uniform voltage distribution among the body diodes of series-connected mosfets. A comprehensive analysis and modeling of gate charge control during voltage transients is presented. The proposed method is experimentally validated on two series-connected SiC mosfets operating in buck mode (dc–dc) and half-bridge inverter mode (dc–ac) at a 1.5 kV dc bus voltage, with switching frequencies up to 40 kHz.