A Hybrid Solid State Transformer (HSST) based on Two-Stage Medium Voltage SST

The concept of the Hybrid Solid State Transformer (HSST) has been introduced in earlier works – an amalgam of a large power low frequency transformer and fractional power solid state transformer. This offers an optimum compromise between cost and controllability, and thanks to its fractional approach, high efficiency. This paper presents an Input Parallel Output Series HSST, using a medium voltage two-stage isolated SST. The predicted peak efficiency of the SST is 96.8% and of the HSST is 98.5%. The HSST unit has been tested to verify the concept and operability.