Reactive power control in MMC HVDC system during ac fault

This paper discusses the reactive power control in multiple modular converter (MMC) HVDC system during ac faults. A control methodology is proposed to solve the overcurrent during and after ac faults. Based on the proposed method, a control strategy is added to the MMC HVDC test to enable the Low Voltage Ride Through (LVRT) function of the converter. The effectiveness of the proposed method in supressing the overcurrent caused by the ac system interruption is verified using electromagnetic (EMT) simulation. The simulation also shows with the proposed LVRT control method, the converter can inject the desired reactive current to the ac system within its ability during the symmetric and asymmetric ac faults.