PITCH MOTION CONTROL OF SPAR-TYPE FLOATING WIND TURBINES

Wave-induced pitch motion has adverse effects on the power generation of Floating Wind Turbines (FWTs). The traditional blade-pitch system, which is commonly used for regulating wind energy capture and power generation, can also be utilized to reduce the platform pitch motion. However, frequent active blade pitching can harm the wind turbine's blade-pitch bearing and gear system, leading to inevitable deficiencies in controlling such wave-induced pitch motion. Many structural control methods have been proposed to mitigate the motion of floating substructures. The present study proposes an active structural control method utilizing a plate hinged at the bottom of a spar-type floating substructure as an external control device. The damping force provided by the hydraulic Power Take Off (PTO) system between the spar and the plate serves as the control force during optimization. The controller is developed under an optimal declutching control framework, in which the damping coefficient of the PTO system is set as a binary function. It is found that current optimal declutching control strategy can effectively minimize the pitch motion of the spar-type substructure and maximize the PTO's power simultaneously. This indicates that more mechanical energy of the spar has been converted into electric energy. The proposed controller is able to reduce the wave-induced pitch motion by more than 21% and increase the PTO power capture by more than 370% at the platform's natural frequency than without control.