Interconnection Frequency Regulation Control Strategy and Method for Offshore Wind Farm and Flexible Direct Transmission System Based on Matching Control

The frequency regulation capability of the onshore power grid can be enhanced by utilizing the linkage effect of two-terminal converter stations in large-scale offshore wind power output of wind turbines. To address the issues of poor coupling and the delayed response between the output power of the far-offshore wind farms and the frequency of the onshore grid, in this paper we propose a grid-forming matching control and strategy for coordinated frequency regulation of converter stations at both sea-land ends. The process of the frequency change of the onshore grid is restored to the offshore wind farm through the coupling of VSC-HVDC DC voltage by symmetric matching control. Furthermore, the wind converter is combined with the virtual synchronous machine based variable damping coefficient load shedding control method, enabling each offshore wind turbine to promptly respond to the frequency fluctuation of the onshore grid without communication and provide the corresponding standby power. A simulation model of large-capacity equivalent direct-drive WTGs connected to the grid via VSC-HVDC is established in MATLAB/Simulink software. The effectiveness of the interconnection frequency regulation strategy between VSC-HVDC and offshore wind power system based on matching control is verified through simulation under weak grid conditions.