Restarting strategy of UPFC series connect unit for fault ride-through based on fault identification

As the latest generation of Flexible AC Transmission System(FACTS) devices, UPFC integrates various flexible control means of FACTS components. Because of the weak insulation capacity of electronic equipment, UPFC fault ride-through capability is limited. This paper introduces the fast fault isolation technique of UPFC, and then a restarting strategy of UPFC series connect unit based on fault identification is put forward for improving fault ride-through capability. Based on comprehensively analyzing UPFC control protection system operation, AC protection operation, power gird status and switch position, the most appropriate operation mode of UPFC such as shutdown, switching mode or restarting to the original mode is determined. For the faults which are determined to restarting, the strategy detects different characteristic quantities for identifying fault recovery for different fault types, the restart of series connect unit is performed when conditions are satisfied. Then discrimination principle and implementation method of the strategy are represented in detail. And based on power flow transfer distribution factor method, the power instruction is adjusted quickly after UPFC restarting caused by remote power gird fault. The strategy is verified in simulation test for Nanjing 220kV power grid UPFC project. The result shows that it has good application feasibility and power grid adaptability, and the strategy can further improve UPFC fault ride through capability.