Mitigating Drivetrain Fatigue of Wind Turbines During Primary Frequency Regulation Below Rated Wind Speed

This paper addresses a critical and often overlooked challenge: drivetrain fatigue in wind turbines (WTs) induced by primary frequency regulation (PFR) operations, particularly below rated wind speed. While existing PFR strategies focus on grid support, they rarely offer mechanisms to simultaneously mitigate the mechanical stress they impose. To overcome this, a Model Predictive Control (MPC) strategy is proposed that adaptively adjusts the PFR gain in real time. First, the boundary characteristics of the de-loading factor under varying wind speeds and PFR gains are systematically analyzed. This analysis bridges a critical gap in prior studies, which predominantly adopted fixed-gain strategies without comprehensively evaluating their fatigue implications. Building on these boundary characteristics, an MPC framework is developed to optimally adjust the frequency regulation gain in real time. This approach achieves an optimization by minimizing drivetrain torque fluctuations for fatigue mitigation, critically informed by a comprehensive boundary analysis of de-loading factors, while rigorously ensuring essential PFR support capability through explicit operational constraints. Extensive simulations demonstrate the superior performance of the proposed MPC, achieving a simultaneous reduction of up to 27.99% in drivetrain fatigue load and 14.44% in frequency deviations compared to conventional methods. This work significantly enhances the mechanical reliability of WTs and facilitates their more sustainable integration into modern power grids by offering a unique solution to a long-standing trade-off.