A resilient model-free controller for power regulation and fatigue load reduction in floating offshore wind turbines

• A dCESO-based ADRC strategy is proposed for collective pitch control of floating offshore wind turbines. • A Red-Tailed Hawk (RTH) optimization algorithm is employed to tune the controller parameters. • The proposed controller improves power regulation and rotor speed stability under turbulent wind and wave conditions. • Comparative results demonstrate enhanced overall performance relative to GSPI, ROSCO, and ESO-ADRC controllers. • The control strategy provides favorable trends in damage equivalent load (DEL) mitigation for key structural components. This paper introduces a model-free control strategy for floating offshore wind turbines (FOWTs), which utilizes a double cascade, two extended state observer (dCESO)-based active disturbance rejection controller (ADRC) to regulate the collective pitch angle of the turbine. The primary objectives are stabilizing the generated power and rotor speed at their rated values while mitigating damage equivalent loads (DELs) on the tower and mooring lines. A data-driven approach employs the red-tailed hawk (RTH) optimization algorithm to fine-tune the controller parameters for optimal performance. The proposed controller is applied to the 5 MW NREL FOWT mounted on a semi-submersible floating platform and evaluated under various operational conditions, including above-rated wind and wave scenarios. Simulation results demonstrate that the dCESO-based ADRC maintains power output and rotor speed at their rated levels, even in challenging environments. A comparison with the standard ADRC, reference open-source controller (ROSCO), and the gain scheduling PI (GSPI) controllers also shows that the optimized controller is better at improving control performance while lowering DELs by a large amount. The ultimate finding reveals that the proposed controller has provided an excellent balance between the performance indicators including the power and the speed errors and the DEL of the tower and the blades, where the power error has been reduced by 48.3% compared to the GSPI, contributing to enhancing the power quality, validating the reliability and effectiveness of the proposed control strategy, establishing it as a robust solution for FOWT applications.