15kV/50A SiC AC Switch Based On Series Connection of 1.7kV MOSFETs

High frequency power switches with higher bidirectional blocking voltages are needed for medium voltage grid applications such as Solid State Transformer (SST). This paper presents a 15kV/50A SiC AC switch based on 1700V SiC MOSFETs in series connection. The AC switch consists of two identical parts in source-to-source connection and each part includes ten 1700V SiC MOSFETs in series. The ten SiC MOSFETs are driven by a common gate signal. The mismatch of the gate signals is a key factor which affects the voltage sharing across the devices. This mismatch is experimentally studied and is less than 10ns. SIMetrix simulations at 12kV/5A turn-off transient is performed based on the tested mismatch time and dynamic balancing capacitor is then designed to achieve satisfactory voltage balance. 10kV/15A single pulse test (SPT) is carried out to verify the feasibility of the designed AC switch. Actual voltage balancing during turn-on and turn-off are experimentally observed. Other functionalities and qualities of the fabricated AC switch are characterized for future SST applications. Auxiliary gate power supplies with 30kV galvanic isolation capability are designed to support the intended medium voltage applications.