Capacitor Voltage Balancing Control Strategy for Converters in 500kV Sunan UPFC

The series and shunt converters of 500 kV Sunan Unified Power Flow Controller (UPFC) substation adopt modular multilevel converter (MMC) structure, but the inaccurate sampling of bridge arm current in low power mode will affect the sub-module capacitor voltage balancing. To overcome this defect, a capacitor voltage balancing control strategy with arm current senseless is proposed, and the submodule capacitor voltage is used to fit the real-time bridge arm current to determine the charge and discharge state of the submodule. A single-loop MMC-UPFC simulation model is built by using MATLAB/Simulink software. The simulation results show that the proposed capacitor voltage balancing control strategy has good control effect in low power mode, which provides a theoretical basis for practical engineering applications.