The influence of power-take-off control on the dynamic response and power output of combined semi-submersible floating wind turbine and point-absorber wave energy converters

Floating offshore wind turbines (FOWTs) have received extensive attention in recent years, particularly after the successful demonstration of several pilot projects, such as Hywind and WindFloat. Integrating wave energy converters (WECs) into FOWTs could potentially help reduce cost of energy by absorbing additional power from waves and introduce restoring moments and extra damping to the floating platform thus reducing motion responses and fatigue loads. In this work, we propose a hybrid floating wind and wave power generation platform, consisting of a semi-submersible FOWT and three point-absorber WECs. Preliminary feasibility study of this concept is performed with verified integrated aero-hydro-servo-mooring numerical simulations. Dynamic response and power output of this hybrid concept are evaluated under several typical environmental conditions. Particularly, different WEC power-take-off control strategies have been comparatively studied, which have shown considerable influences on the platform dynamics and power generation. More specifically, reactive control generally worsen the platform motion responses, while spring-damping control is able to mitigate the pitch motion to certain extent. Regarding power output, reactive control leads to the highest wave power generation, almost twice as much as that of spring-damping, which has been used in most existing works on hybrid power generation system. Moreover, it is found the optimal control design for point-absorber WEC attached to fixed structures is no longer optimal for the combined floating wind and wave energy production platform, which needs further investigations in the future.