Coordinated Control Strategy for Improving Frequency Stability of Offshore Wind Farms Connected to the Grid through MMC-HVDC Transmission

Aiming at the inertia support problem of offshore wind power connected to MMC-HVDC transmission, a virtual inertia control strategy based on DC capacitor energy and wind turbine rotor kinetic energy is proposed. By analogy with the inertia response of the synchronous machine, the energy of the DC capacitor is used to provide inertia support. For wind turbines with different wind speeds, a coordinated inertia support control based on differential rotor kinetic energy regulation is designed. The frequency fluctuation is reflected by the change rate of DC voltage to realize the inertia support of the wind farm to the system. Aiming at the primary frequency regulation problem of the receiving-end AC grid, by establishing the coupling relationship between DC voltage and AC grid frequency, a wind farm frequency regulation control strategy based on the measurement information of the DC voltage deviation is designed, and the variable speed control of the wind turbine is used to realize the wind farm actively participates in the primary frequency regulation. Finally, based on the RTLAB OP5600 real-time digital simulation platform, the simulation model of offshore wind farms connected to the grid through MMC-HVDC transmission is built to verify the effectiveness of the proposed control strategy.