AN SiC-based soft-switching and self-power supply MMC for MVDC

Here, a novel modular multilevel converter (MMC) and its associated control scheme are proposed for medium-voltage direct-current (MVDC) distribution systems. The voltage gain and power can achieve wide-range expansion by expanding sub-modules. The voltage, current, and power are shared among all sub-modules. In addition, all semiconductor devices implement soft switching under low voltage stress and current stress by introducing an auxiliary cell in each sub-module. By reasonably distributing the energy collected in the soft switching process, the converter realizes the self-power supply for the drive control circuit of the high-potential semiconductor switches, wherein the sub-modules are turned on step by step. The structure of the converter is described and its working principle and control strategy are analyzed in detail. Finally, a 1.8 kW experimental prototype based on SiC devices is provided to achieve an efficiency of 97.3%.