The grounding design of MMC-UPFC

Based on the functional requirement for MMC-UPFC, 3 grounding proposals were brought up i.e. interface-transformer valve side star connected grounding, AC side large inductance grounding and AC side zig-zag transformer grounding. Also, the winding connection form of converter transformer and the grounding impedance of 3 grounding methods were investigated. Through the simulation and analysis of the fault characteristics of internal ac bus and dc bus fault, the relationship between grounding impedance and internal electrical quantities of valve was derived. With considerations of the fault characteristics of 3 grounding methods and domestic technology ability, the conclusion that interface-transformer valve side star connected grounding is more advantageous in MMC-UPFC was derived.