DC Overvoltage Analysis of GFM-controlled Wind Farm Connected via MMC-HVDC System Caused by Receiving-end AC Faults

DC overvoltage occurs when short circuit fault exists at the receiving-end and is harmful to the safety of the system where wind farms are connected to the grid through high-voltage direct current (HVDC) transmission based on the modular multilevel converter (MMC). To address this issue, this paper first analyzed the mechanism of the DC overvoltage and innovatively proposed a strategy in which grid-forming-controlled wind farms are integrated into the AC grid through MMC-HVDC, whose sending-end applies grid-following control and constant DC voltage control. However, secondary DC overvoltage appears during the fault recovery stage and is mainly caused by the saturation of the PI controller of constant active power control. Simulations are carried out on a test with MATLAB/Simulink, and results verify the efficacy of the proposed methods in suppressing DC overvoltage that appeared during receiving-end faults and their recovery stage.