A combined wind-storage primary frequency regulation method considering low-speed shaft fatigue loads in wind turbine

Wind turbine (WT) engagement in frequency response enhances overall system frequency stability. However, it concurrently results in elevated fatigue loads on the low-speed shaft (LSS). To mitigate the fatigue loads on the LSS while maintaining system frequency stability, this paper introduces a comprehensive wind-storage primary frequency regulation (PFR) method, which takes into account the fatigue loads on the LSS of the WT. Initially, the impact of PFR on the fatigue loads of the LSS in the WT is analyzed. To mitigate the LSS ' s fatigue loads, an improved torsional vibration control method based on generator speed is introduced. This method markedly decreases LSS fatigue loads. The fatigue loads can be reduced by 20.94 %. However, torsional vibration methods may intensify WT output power fluctuations, which pose issues for LSS torsional vibration suppression. Building on this foundation, a combined wind-storage strategy utilizing a low-pass filtering algorithm is proposed. Supercapacitor (SC) storage undergoes charging and discharging in response to frequency changes to achieve WT power smoothing. The validity of proposed method is confirmed through time-domain simulation. The results demonstrate that the proposed method reduces system frequency fluctuations with the frequency deviation being reduced by around 50 %. Additionally, it can further decrease the damage equivalent load of the LSS by more than 9 %. Finally, by comparing the proposed method against a fuzzy logic-based wind-storage coordinated method, the effectiveness of the proposed method is verified.