Control Strategy for Voltage Source Converter-Based HVDC System under Unbalanced Voltage Conditions

The mathematical model of voltage source converter-based flexible DC transmission system (VSC-HVDC) and traditional fault control strategy are comprehensively analyzed. The proportional resonant controller in the traditional dual vector current controller is proposed to simplify the structure of traditional inner current controller. The proposed method improves the response speed and control accuracy of the control system. According to the output voltage distortion caused by the DC voltage ripple, the PWM with amplitude-adjustable carrier is adopted, and according to the DC side voltage rise the power setting value is adjusted. Finally, the control strategy is verified by the electromagnetic transient simulation software PSCAD/EMTDC, the simulation results show it can effectively restrain the fault overvoltage, improve the operation ability of the system.