Optimal ancillary control for frequency regulation of wind turbine generator based on improved fatigue load sensitivity

Frequency regulation adjusts the power or torque of the wind turbine generator (WTG) without considering the operating dynamics of WTG’s shaft and tower, which results in a significant increase in the fatigue load experienced by the shaft torque and tower bending moment. In that, this paper proposes an optimal ancillary control (OAC) method to mitigate the above-mentioned fatigue load. The establishment of the OAC method includes the improvement of fatigue load sensitivity calculation accuracy and the formulation of optimization objective and constraints. Most importantly, the dual-mass drive train and wind speed fluctuations are considered by the fatigue load sensitivity. Moreover, the minimization of the fluctuation of main shaft torque and tower fore-aft bending moment is employed as the optimal objective. Finally, the dynamic adjustment of the power reference is reflected through the constraints. As a result, the OAC method can significantly reduce the WTG fatigue load and thus improve the system frequency stability. Case studies are conducted under various working conditions. By analyzing the damage equivalent load, rainflow cycles and frequency response, the effectiveness of the proposed method is verified.