Voltage Balancing Control of Series-Connected SiC MOSFETs by Using Energy Recovery Snubber Circuits

Power semiconductor switches are usually connected in series to achieve higher blocking voltage. However, the series-operation of semiconductor devices is not easy due to unequal voltage sharing. In comparison with silicon (Si) devices, series-connecting silicon carbide (SiC) devices are even more challenging due to their ultrafast switching speed. In this article, a novel snubber circuit topology with energy recovery capability is proposed to control the voltage sharing of series-connected SiC mosfets. The snubber circuits operate with a self-balancing technique; thus, the required control and sensing circuits are simple. The proposed method maintains the snubber capacitor voltage nearly constant, so the snubber capacitors are not fully discharged during the devices on-state. Besides, excess snubber energy can be transferred back to the dc bus, so the induced snubber loss is minimal. Experimental results show the effectiveness of the proposed snubber circuit topology in a half-bridge inverter with four SiC mosfets connected in series.