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

High voltage power switches are needed for medium-voltage (MV) grid applications such as Solid-state Transformers. The series-connection of low voltage devices is a cost-effective alternative approach to achieve higher blocking voltages. Furthermore, all reported high voltage SiC switches to date are unidirectional voltage blocking devices. Additional devices or power stages such as unfolding bridges are needed for MV AC applications. Combining high blocking voltage and bidirectional operation capability into one single module is, therefore, very attractive for future MV AC applications. This paper proposes a forced-air cooled 15 kV/50 A SiC AC switch based on the series-connection of 1700 V SiC MOSFETs. The AC switch consists of two identical parts connected source-to-source. Each part includes ten 1700 V SiC MOSFETs in series. Each set of ten SiC MOSFETs are driven by a common gate signal. A quantitative switching transient model is developed to expound on how multiple critical factors affect the voltage balancing during the switching transient. A preliminary voltage balancing performance is predicted using the proposed model. A dynamic balancing dV/dt snubber capacitor is then designed to achieve satisfactory voltage balance. A 10.5 kV/30 A double pulse test (DPT) is carried out to verify the feasibility of the designed AC switch and the validity of the proposed switching model. Necessary electrical characteristics of the fabricated 15 kV SiC AC switch are characterized for future applications. Auxiliary gate power supplies with 30 kV galvanic isolation capability are designed to support the intended MV applications. Based on the 15 kV SiC AC switch, a 7.2 kVac/100 kVA series resonant converter is developed and experimentally demonstrated to further verify the feasibility of the proposed device stacking technology.