Design and Implementation of a 7.2kV Single Stage AC-AC Solid State Transformer Based on Current Source Series Resonant Converter and 15 kV SiC MOSFET

This paper introduces a 97% efficiency medium voltage (MV) Solid State Transformer (SST) based on two level single stage (TLSS) topology and 15 kV SiC MOSFETs. Series resonant converter (SRC) is implemented as the main stage and is identified as a current source (CS) SRC for the first time. Equivalent resonant frequency of the proposed CS-SRC is analyzed in both time domain and frequency domain. Resonant frequency calculation equation is derived and can be used to accurately design the resonant tank. Zero voltage switching (ZVS) for 15 kV SiC MOSFET in CS-SRC topology under extremely wide input voltage from OV to 10 kV is analyzed and designed at a medium frequency (MF) of 40 kHz. Partial discharge for the 15 kV SiC MOSFET's parasitic capacitor are explained and the associated turn on loss equations are derived. Magnetizing inductance L-m and deadtime t(dead) are further optimized based on the trade-off between the turn on loss and conduction loss of the semiconductor devices. A fully functional and compact SST based on the proposed concept is developed and tested with an input of voltage of 7.2 kVac and from 1 kW to 12 kW. The efficiency is higher than 97% under most load conditions.