Complementary Control Strategies for Floating Offshore Wind Turbines: Gain Scheduling With LQG Enhancement and Equivalent Wind Speed–Based Individual Pitch

ABSTRACT This study investigates control strategies for large‐scale floating offshore wind turbines using the semi‐submersible IEA 15‐MW turbine as a benchmark. A gain‐scheduled PI (GSPI) controller is firstly established as the baseline for collective pitch control (CPC). On this basis, LQR and LQG controllers are designed to generate supplementary pitch increments, aiming to enhance regulation performance and load mitigation capability. Subsequently, an Equivalent Wind Speed–based Individual Pitch Control (EWIPC) strategy is integrated with the LQG scheme to further reduce blade unbalanced loads caused by wind shear and tower shadow. Comparative simulations are conducted among three CPC schemes—GSPI, LQR, and LQG—and the integrated LQG + EWIPC scheme under turbulent wind and irregular wave conditions. Results demonstrate that LQR and LQG achieve comparable control performance, both significantly outperforming GSPI in reducing generator speed and power fluctuations (standard deviation reduction of approximately 39%). Regarding system stability, LQG + EWIPC achieves the lowest mean tower displacement and platform pitch, with reductions of 45.3% and 15.7%. The combined LQG + EWIPC scheme reduces the standard deviations of blade root bending moment fluctuations by 19.3%–39.3% across the three blades, respectively, and reduces the PSD at the 1P frequency by approximately 50% compared with CPC, despite introducing some blade load asymmetry and slightly increased pitch activity. Overall, the proposed LQG + EWIPC strategy effectively enhances control performance, system stability, and load mitigation, providing a solid basis for future control system development in offshore wind energy.