Start-up scheme for solid state transformers connected to medium voltage grids

The development of the high voltage wideband gap semiconductor SiC power devices has enabled the solid state transformer (SST) technology in connecting a medium voltage grid to a low voltage grid. Though, these power devices have superior loss and switching characteristics compared to Si power devices, they have limited inrush current handling capability. The large inrush currents that flow into the SST from the grids when commissioning the SST system can be detrimental to the SiC devices. A proper start-up scheme is required to address this issue. Reported literatures on SST are focused on different topologies and their control aspects. This paper is focused in developing the safe start-up schemes for SST system connecting medium voltage grid to low voltage grid. The paper presents the simulation results and experimental verifications of the proposed SST start-up scheme.