Full ZVS soft-start of a SiC medium voltage series resonant DC-DC converter using variable frequency variable duty cycle control

摘要

A novel variable frequency variable duty cycle (VFVD) control scheme using off-line digital control by only sensing the output voltage is proposed. Designed for a 6 kV 40 kHz series resonant DC-DC converter in solid state transformer application, it realizes cycle-by-cycle resonant current limiting and zero voltage switching (ZVS) at any load condition. According to the state plane analysis, with a certain output voltage, the resonant current can be well controlled by modifying the on-time, and ZVS of the medium voltage (MV) SiC devices can be ensured by adjusting the switching frequency. By sensing the output voltage, a digital controller with off-line lookup table can be easily implemented. Full ZVS together with fast current limiting greatly improves the reliability of the MV medium frequency converter.