Study on load reduction and vibration control strategies for semi-submersible offshore wind turbines

Independent pitch control (IPC) is a crucial technology for enhancing the performance of wind turbines, optimizing the power output, and reducing the loads by managing each blade. This paper explores the primary vibration modes of semi-submersible wind turbines under wind-wave coupling. Given the effectiveness of pitch control in vibration suppression, this paper addresses the limitations of conventional collective pitch control (CPC) by designing an independent pitch control method based on an equivalent wind speed model (EWIPC). This model constructs an effective representation of the actual wind speed's influence on pitch angle by comprehensively considering the spatial distribution of wind speeds. This way, the control accuracy and response speed are significantly improved, making the control strategy more intuitive and efficient in complex wind speed environments. The proposed independent pitch control method is validated through simulations on the International Energy Agency (IEA) 15 MW wind turbine. The simulation results indicate that the EWIPC stabilizes wind turbine power output and reduces structural loads. Additionally, it demonstrates significant effectiveness in reducing vibrations of the blades and tower, as well as in eliminating 1P oscillations in the blade root bending moment.