Study on Load Reduction and Vibration Control Strategies for Semi-Submersible Offshore Wind Turbines

Independent pitch control is a crucial technology for enhancing the performance of wind turbines by effectively managing each blade to optimize power output and reduce loads. 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, the study addresses the limitations of conventional unified pitch control. It proposes an independent pitch control method based on an equivalent wind speed model. This model simplifies the analysis of wind speed effects on blade angle adjustments, thus improving control accuracy and response speed. The equivalent wind speed model, which integrates the spatial distribution of actual wind speeds, provides an effective description of how true wind speed affects pitch angles. This approach makes control strategies more intuitive and efficient in complex wind speed environments. The proposed independent pitch control method was validated through simulations on the IEA 15MW wind turbine, demonstrating its effectiveness and performance. Experimental results indicate that the equivalent wind speed model-based independent pitch control method significantly reduces structural loads, vibrations in blades and tower, and 1P oscillations in root bending moments while maintaining stable power output. The research findings offer valuable insights for load reduction and vibration suppression control in offshore floating wind turbines.