Abstract: In low frequency AC transmission system (LFAC), offshore wind farm is unable to respond to changes in onshore grid frequency in a timely manner due to frequency decoupling and signal transmission delays between the offshore wind power system and the onshore AC system. For this reason, this paper proposes a control strategy to improve the active frequency support capability of offshore wind farms by combining the system inertia. In terms of frequency signaling, an additional frequency sag controller is designed based on the V/f control strategy of the low-frequency-side structure network of the modular multilevel matrix converter (M3C), combined with the system inertia. The frequency coupling link between the M3C net side and the low-frequency side is established, so as to realize the real-time transmission of frequency information between the two sides. In terms of frequency support, when the system is disturbed to generate frequency deviation, the offshore wind turbine can adjust the power command value through additional droop control, thereby providing frequency support for the system. Finally, the effectiveness of the proposed coordinated control strategy is verified in MATLAB/Simulink through the simulation of load change and three-phase AC short circuit fault.

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