Fast Frequency Control of MTDC System Integrated Offshore Wind Farms Based on Short-Term Power Overshoot

Renewable energy systems are required to provide fast frequency support to the power grid for maintaining frequency stability. For the offshore wind farms (OWFs) integrated into the bulk power grid by multi-terminal direct current (MTDC) systems, the challenges for realizing fast frequency control consist of coordination of OWFs with different wind speeds and limited communication condition. Address those challenges, this paper proposes a fast frequency control (FFC) method for MTDC integrated OWFs based on short-term power overshoot. The frequency-DC voltage droop control is used to transmit the frequency deviation signal from the onshore power system to the OWFs without long-distance communication dependency. Then, the FFC is applied to the wind turbine (WT) power control loop, allowing the OWF to respond to frequency fluctuation and further support the onshore power system by use of the rotor kinetic energy according to short-term power overshoot reference. Moreover, the coordination strategy of OWFs with different wind speeds are proposed, which adaptively adjusts the power control coefficients according to real-time rotor speeds. Simulation results show that the proposed method can respond to grid frequency fluctuation in time and can effectively coordinate the OWFs for supporting the grid frequency.