A Restart Strategy of Bipolar Short-Circuit Fault for MMC based Power Electronic Transformer

This paper describes the fault characteristics of power electronic transformer (PET) based on modular multilevel converter (MMC). The bipolar short-circuit fault on MV DC side is analyzed. The influence of the fault on instantaneous power of the MMC bridge arm and sub-module capacitor voltage is estimated with mathematical deduction. The fault ride-through ability of PET is discussed as well. As for the bipolar short-circuit fault on MV DC side, a restart strategy after fault with the maximum time of fault clearing is proposed. The restart strategy has the advantages of low impact and high speed, and has been verified by simulation and 10kV PET prototype.