The mechanism and suppression strategies of oscillating current between the shunt and series converters of 35kV MMC-UPQC

Unified Power Quality Conditioner (UPQC) based on a modular multi-level converter (MMC) (referred to as MMC-UPQC) is more suitable for high-voltage large-capacity applications. Because of short electrical distance and strong electrical coupling, there may be oscillating current between shunt and series converter of MMC-UPFC. Based on accession to the grid and practicable grounding design, the equivalent differential mode and common mode oscillating circuit of MMC-UPQC were obtained. And through the equivalent oscillating circuit and MMC-UPQC works principle, the mechanism of oscillating circuit was drawn. Finally, two methods closed-loop suppression and virtual resistance was designed to suppress the oscillating current, and, Validated by RTDS simulation.