Torsional oscillation damping control for DFIG-based wind farm participating in power system frequency regulation

Large scale wind farms (WFs) are gradually required to participate in power system frequency regulation especially in a weak grid. Corresponding ancillary frequency control functionalities and the contribution of the WF to system frequency stability are well studied. However, the impact of WF ancillary frequency control on wind turbine generators (WTGs) is rarely considered. It is found in this paper that the ancillary frequency control deteriorates drive-train torsional oscillation of the WTG, which restricts application of the ancillary control. Therefore, the WF may not be able to fulfill grid code requirements. To overcome this problem, this paper proposes a damping control scheme based on reactive power modulation of the WTG to suppress drive-train torsional oscillation, which is beneficial to the WF to meet the grid code requirements. Moreover, superior to the traditional active power modulation method, the proposed control scheme can achieve satisfactory damping improvement with less control effort in a weak grid. Feasibility and effectiveness of the proposed damping control scheme are validated by simulations.