A novel precharge control strategy for modular multilevel converter

In order to make the DC voltage of high voltage direct current system based on modular multilevel converter (MMC-HVDC) rise to the rated value smoothly and quickly, the novel closed-loop precharge control strategy is put forward with respect to DC side voltage and AC side voltage. Adopting current closed-loop feedback control to regulate a constant charging current, two control strategies can effectively reduce the precharge time and eliminate the current surge. Then, the relationship between AC voltage drop ratio, the system short circuit ratio and current-limiting resistance is deduced and application scope of two control strategies is proposed respectively. At last, a simulation model of three-terminal MMC-MTDC system is built to verify the validity of the proposed control strategies based on the PSCAD/EMTDC.