Design and Analysis of a 270kW Five-level DC/DC Converter for Solid State Transformer Using 10kV SiC Power Devices

Enabled by high voltage fast switching SiC devices, solid state transformers (SST) are being considered as a feasible application and a major step forward compared with conventional power transformers. One of the key components for the SST is a high voltage high frequency DC/DC converter. To reduce size and weight of this DC/DC converter, high frequency operation is desired hence it requires high voltage fast switching power devices like SiC MOSFETs. Due to the high frequency used, there is still significant amount of losses in the SiC MOSFETs and PIN diodes. In this paper, a five-level DC/DC converter is proposed based on the concept of three-level DC/DC converter with a flying capacitor. A key characteristic of this DC/DC converter is that it allows soft-switching turn-on operation for the SiC power MOSFETs, hence eliminating a major loss component for the SiC devices. This topology-related ZVS capability, coupled with superior conduction and switching performance of SiC MOSFETs and PIN diodes, facilitates the selection of 20 kHz switching frequency as the target frequency for a high power SST application.