Research On Individual Pitch Control For Wind Turbines

High-capacity per unit, variable pitch control and variable speed constant frequency is the trend of wind power technology. High-capacity per unit means that the diameter of the wind turbine is larger. Then under the influence of turbulence, wind shear and tower shadow effect, wind speed on the swept surface is not uniform, so during the blade rotation, the vibrations of blades, nacelle, tower, drive shafts and other components will be caused, which result in the fatigue load and reducing the service life of the wind turbine. If individual pitch control technology is used, that is each blade pitch angle adjusted asynchronous according to different expected angles, the fatigue load is able to reduced, as well as the unit life will be extended.Firstly, individual pitch control strategies are compared and different kinds of loads are studied. The shaft torque, flapwise bending moment and edgewise bending moment are simulated and analyzed using load analysis software. Torque measurement methods are studied and the drive train torque measurement method is further studied.Secondly, a variable pitch wind turbine model is established, including the wind turbine model, the drive train model, the doubly-fed machine model, and the variable pitch control model. The application conditions of the wind turbine model based on the aerodynamic theory and based on the blade element theory are analyzed and compared. The equivalent assumptions of the flexible shaft model, rigid shaft model, and the lumped model are discussed.Finally, an indirect estimation method for a wind turbine using double-fed induction generator is proposed. The electromagnetic torque calculation model based on electric power, as well as the two-mass torsional model, including the blades, low speed shaft, gear box, high speed shaft and generator is established. The torsional torque and the wind turbine torque are calculated based on the model. The simulation results indicate that the torsional torque calculated by the model is consistent with the theoretical value, which is the foundation to further realize the application of MIMO individual blade pitch control system.