Simulation of Grid Paralleling Devices based on back to back VSC-HVDC Converted into UPFC

Abstract

The back-to-back VSC-HVDC paralleling device structure is similar to the unified power flow controller (UPFC) circuit structure. After completing paralleling operation, the back-to-back VSC-HVDC paralleling device can be converted into the UPFC device through relevant electrical operations. Aiming at the problem of power and frequency fluctuation in the process of conversion, a method of using circuit breaker and switch state as characteristic signals to block or open the signal of parallel side and series side converter is proposed.By this method, a smooth transition from back-to-back VSC-HVDC paralleling device to UPFC device is realized. The method is verified by PSCAD/EMTDC simulation.