Coordinated Control Strategy to Enhance FRT Capacity for Offshore Wind Farms Connected MMC-HVDC

Abstract

AbstractVSC-HVDC technology is the first choice for large-scale offshore wind power grid connection in the deep ocean. Offshore wind farms connected MMC-HVDC system should have fault ride-through (FRT) capability when the grid side fails. Currently, DC Chopper is commonly used to achieve FRT, but the capacity of DC Chopper is usually the rated capacity of the wind farms, and the switching time is long, resulting in high project cost. To address the problem of large design capacity and long switching time of the existing DC Chopper, this paper proposes a non-communication coordinated control method between DC Chopper and wind farm side converter and wind farms. When a fault on the grid side causes the DC voltage to exceed the action threshold of the DC Chopper, the DC Chopper is used to initially absorb the unbalanced power. If the DC voltage continues to rise to exceed the action threshold of the voltage drop method, the wind farm side converter reduces the input power by reducing the amplitude of the AC bus voltage of the wind farms and cooperating with the wind farms to reduce the active power. The proposed method not only reduces the rated capacity and switching time of DC Chopper, but also limits the DC voltage to the allowable value more quickly, and the system can achieve safe and reliable FRT.KeywordsOffshore wind farmDC chopperCoordinated control