Autonomous frequency smoothing control of offshore wind-linked HVDC for low-inertia system

As international attention toward carbon neutrality has increased, making offshore wind a promising and dominant renewable energy source. The inherent uncertainty and volatility of renewable energy sources aggravates the difficulty of system operations. Therefore, the electrical grid requires that the wind generators participate in frequency control. However, in the case of large-scale offshore wind farms, the offshore frequency is independent of the onshore frequency owing to the connection through a high-voltage direct current (HVDC) system. This paper proposes a sustainable control method that flattens the frequency fluctuation caused by wind generation in normal state. By adopting communication-free frequency control through offshore wind farm HVDC systems, severe wind fluctuations can be controlled. The proposed scheme allows offshore wind power to participate in onshore frequency regulation using only local measurements without any communication. System frequency response and control stability trajectory analyses were also performed. Moreover, an adaptive gain was proposed to achieve more sustainable control for various wind conditions. The simulation results show that this autonomous frequency smoothing control is suitable for large-scale offshore wind farms with HVDC and significantly contributes to frequency regulation. The proposed frequency smoothing control can contribute to carbon neutrality in power systems with low inertia and reduced frequency regulation reserves.