Fault characteristics analysis and protection design for MMC-UPFC with high reliability

Unified Power Flow Controller based on Modular Multi-Level Converter (MMC-UPFC) is considered as the most Flexible AC Transmission System (FACTS) device, as it can control the power flow and enhance power system stability. The fault characteristics and the protection design are important for MMC-UPFC with high reliability, but relevant researches are incomplete. This paper analyzed the topology structure and working principle of MMC-UPFC, and then studied the operating characteristics under single-phase grounding fault and two-phase short circuit fault condition. Furthermore, according to the characteristics of UPFC device and different structures of the series and parallel side, the overall protection design of the MMC-UPFC device is presented. At last, the simulation analysis based on PSCAD software verified the effectiveness of the design.