Exosystem-Based Dynamic Input Control Strategy for Load Mitigation in Variable-Speed Wind Turbines Under Above-Rated Wind Conditions

Abstract

Despite the significant progress in wind power generation in recent years, how to mitigate the structural fatigue loads on critical components while regulating power output, thereby extending the service life of wind turbines (WTs), remains a highly concerned and challenging research topic. In this article, an exosystem-based dynamic input control strategy is proposed for variable-speed WT (VSWT) systems operating above-rated wind speed to achieve this dual objective. Specifically, the nonlinear VSWT model describing the drive-train dynamics, tower dynamics, and pitch actuator dynamics is first linearized and represented as a linear parameter varying model. Subsequently, an exosystem for simulating the external disturbance signal and the desired reference signal is incorporated into the dynamic input control strategy, aiming to reduce the difficulty of solving multiobjective optimization control problems. In addition, to improve the accuracy and real-time performance of the measured wind speed, the continuous wave light detection and ranging (CW-LIDAR) simulator is used to provide the effective wind speed value, and exosystem dynamics are constructed using the CW-LIDAR measurement data. Finally, comprehensive comparative studies between the proposed scheme and several pitch controllers are conducted under multiple scenarios using the OpenFAST (fatigue, aerodynamics, structures, and turbulence) platform on the NREL 5-MW VSWT, thereby verifying the feasibility and effectiveness of the proposed strategy.