Voltage Balancing Method for Series-Connected SiC MOSFETs Under No Load Condition

Voltage Source Converters (VSCs) serve as vital interfaces between DC and AC systems, playing a pivotal role in medium DC distribution systems. VSCs using series- connected SiC MOSFETs can increase power density and reduce footprints, which is significant for urban gird applications. To balance the voltages of series-connected SiC MOSFETs, an active clamping module (ACM), including an auxiliary switch and a capacitor, is paralleled with each device. The device voltages are balanced as long as ACM capacitor voltages are balanced. A balancing control method is proposed to balance ACM capacitor voltages under no-load condition: select half of the ACMs in two phase legs and recycle the energy back to DC bus. By assigning a pulsing gate signal to ACMs with higher voltages in dead time, the voltage balance can be achieved. There are two manners of selecting ACMs based on the sorting method: voltage sorting in each arm separately and sorting in both arms together. A VSC built with 4 series-connected SiC MOSFETs is tested under no load condition and the devices are well balanced.