This paper proposes a novel two-stage dc–ac converter for realizing a 7.2kV medium-voltage (MV) solid-state transformer (SST) based on half bridge LLC resonant converter and 15kV SiC AC switch. A new half bridge LLC resonant converter combined with AC switch is proposed to address major challenges in MV dc-ac converters such as achieving soft switching for the MV MOSFETs across wide voltage and load ranges. The topology is analyzed with both time-domain analysis and first harmonic approximation to provide useful equations for circuit design. Soft switching behavior over wide voltage range is investigated, and calculation of the associated loss distribution is presented. The 15kV SiC AC switch has been tested under signal pulse at a DC voltage of 10kV/15A. Necessary electrical features of the fabricated AC switch are characterized for power converter system design. A full-scale and compact SST that converts 7.2 kVac to 800Vdc is developed to verify the theoretical analysis.
