Turbulence intensity identification and load reduction of wind turbine under extreme turbulence

Abstract

A novel turbulence intensity identification method is proposed based on wind turbine operating data, by combining the wind reconstruction and pitch rate. In the torque control stage, a simplified mathematical model of a wind turbine is established, from the measured rotor speed and generator torque, and an immersion and invariance estimator is used to estimate the real-time wind speed. In the pitch control stage, the simulation results show that the blade pitch rate is closely related to the turbulence intensity, so the rate change of pitch angle was used to indirectly estimate the turbulence intensity. Based on the turbulence intensity identification method, a load reduction strategy for wind turbines under extreme turbulence condition is proposed. As this load reduction strategy may reduce power generation, a mathematical model for load reduction optimization is established, and the dichotomy method was used to find the extreme value of the function to resolve the conflict between load reduction and power generation. Simulation and comparison of loads on a 4.2 MW wind turbine before and after the application of the new strategy showed that within the wind speed range of 14 m/s-20 m/s, the ultimate loads of the hub moment along the y-axis (hub coordinate system) and tower top moment along the y-axis (yaw bearing coordinate system) were reduced by 17% and 19%, respectively.