Coordinated Control Strategy of Inertia Support for MMC-HVDC Connecting Offshore Wind Farms Considering Frequency Secondary Drop

Aiming at the problems of low inertia support capability and poor frequency stability of power electronic power system, a coordinated control strategy for rapid recovery of wind power speed is proposed to effectively avoid the frequency secondary drop (FSD). An adaptive speed recovery strategy based on variable droop coefficient is designed by logistic function to reduce the power impact of wind power on the system at the moment of inertia support control. On this basis, an adaptive switching strategy for the sub-modules (SMs) of the sending and receiving converter stations is proposed. The energy support margin of MMC-HVDC capacitor is used to compensate the power loss caused by the speed recovery of the wind turbine (WT). The starting criterion and related control parameters are designed based on the key characteristic quantities, which can improve the speed recovery speed while avoiding FSD. Finally, based on the real-time digital simulation platform, a simulation model of MMC-HVDC connecting offshore wind farms is built to verify the effectiveness of the proposed coordinated control strategy.