Pitch motion control of spar-type floating wind turbines

Yu, Shuang-Rui and Zhang, Ming and Chen, Ming-Lu and Yuan, Zhi-Ming; (2023) Pitch motion control of spar-type floating wind turbines. In: Proceedings of the ASME 2023 42st International Conference on Ocean, Offshore and Arctic Engineering. ASME, AUS.

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Wave-induced pitch motion has adverse effects on the power generation of Floating Wind Turbines (FWTs). As a main structure to regulate wind energy capture and power generation, the traditional blade-pitch system is not a good choice for controlling such wave-induced pitch motion. There will be trade-offs when fullfilling multiple objectives with a single control system, and frequent active blade pitching is harmful to the wind turbine's bearing and gear system. Hence, many structural control methods have been proposed to mitigate the motion of floating platforms. The present work 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 is the control force during optimization. The plate is relatively small, but can validly increase the moment of inertia of the hinged system in the pitch direction. The controller is developed under an optimal declutching control framework. In declutching control, the damping 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 capture at the same time. This indicates that the mechanical energy of spar has been converted into electric energy. The proposed controller is able to reduce the wave-induced pitch motion by 21.1% and increase the power capture by 314.3% at the fixed target frequency.