A Novel Coordinated Control Strategy for Frequency Regulation of MMC-HVDC Connecting Offshore Wind Farms

To solve the problems of weak inertia support and poor frequency regulation capability of power system, a novel coordinated control strategy for frequency regulation of MMC-HVDC connecting offshore wind farms (OWFs) is proposed to improve system frequency stability. In terms of inertia support, based on analyzing the available energy margin of MMC-HVDC, a virtual inertia control method based on decoupling control of DC voltage and capacitor voltage is proposed, which can fully utilize the energy margin of capacitors and improve its inertia support capability. The coupling relationship between the rotor speed of wind turbines and the frequency is directly established through DC voltage, an inertia support coordinated control strategy for MMC-HVDC and OWFs is designed to realize the rational utilization of available energy. In terms of primary frequency regulation, according to the local DC voltage, a primary frequency regulation control strategy is proposed for OWFs based on the variable speed control and pitch angle control. The overall coordination is realized through the reasonable design of control links and parameters, so as to improve the frequency stability of the system. Finally, the simulation model of MMC-HVDC connecting OWFs is built to verify the validity of the proposed control strategies.