Vibration reduction strategy of offshore wind turbine under wind and wave loads

For purpose of studying the influence of wave on the wind turbines, the causes of aerodynamic load fluctuation and the aerodynamic torque ripple of hydrodynamic frequency is analysed in the mechanism by using the wave model. According to the formation mechanism, the existence of the ripples is verified on GH Bladed platform. To reduce the ripples caused by wind shear, tower shadow and waves of offshore wind turbine, a pitch control strategy is presented in this paper. Firstly, the integral gain of the top tower vibration acceleration signal is combined with the reference pitch angle value to reduce the uniform pitch. Then designing a low-pass filter to filter out the 3P output power ripple of the wind turbine, and converted into adjustment of individual pitch angles of three blades according to rotor azimuth, and superimposed with the changed uniform pitch angle at last. Simulation results indicate that the designed pitch control strategy can not only alleviate the 1P aerodynamic load ripple, but also suppress the aerodynamic torque and output power ripples at 3P and hydrodynamic frequency. The proposed pitch control strategy can reduce wind turbine fatigue loads and improve the output power quality.