Voltage Balancing Control with Capacitor Charging Method for Series Connected SiC MOSFET Submodules

Device series connection is a method to achieve higher blocking voltage with multiple devices. However, a voltage unbalance among the series connected devices is a critical issue that may lead to a failure of the devices. The unbalance can be caused by difference of device characteristics and mismatch of gate signals due to delay of external gate drive circuit. In this work, a voltage balancing control (VBC) for series connected SiC MOSFET submodules is studied to solve the unbalance issue. One submodule consists of two switches and one shunt capacitor. By charging or discharging the shunt capacitor, voltage balancing can be achieved. The VBC is experimentally verified with four series connected SiC MOSFET submodules up to 3 kV DC voltage. Voltage balancing is achieved within 5 % of an expected balanced voltage.