UPFC fault ride-through strategy based on virtual impedance and current limiting reactor

Abstract

When a fault occurs on the line equipped with Unified Power Flow Controller (UPFC) based on Modular Multilevel Converter (MMC), it may cause the blocking of MMCs and then make UPFC out of operation. To avoid the non-function of UPFC under the condition of external fault, a UPFC fault ride-through (FRT) strategy is proposed based on the analysis of fault characteristic. The FRT strategy is realized by adding virtual impedance (VI) loop in the Shunt Side MMC control process and connecting a Current Limiting Reactor (CLR) on the DC bus to limit the valve-side current of shunt side and the fault current fed through the DC bus from the Series Side MMC. Furthermore, the evaluating indicators and the value selected method for VI and CLR are provided, and the values of VI and CLR are discussed. Finally, simulation results based on PSCAD/EMTDC verify the fault characteristic and the effect of proposed FRT strategy.