Wind Turbine Load Control Based On Dynamic Coupling

The wind turbine size and structural flexibility increasing,low-frequency fluctuations in wind turbine load easily lead to vibration of drive tarin,tower and blade.In view of the load control of wind turbine,the main research work is as follows:1.Study the load characteristics of the rotor under complex wind conditionsAccording to the wind shear index model,the influence of wind shear index and wind turbine diameter on wind turbine load is analyzed.The influence of the tower on the wind speed distribution was analyzed by using the windward tower effect model.Based on the Kaimal spectrum,the wind turbulence model is established to analyze the effect of turbulence on the wind velocity distribution on the wind turbine surface.The results show that the wind shear and tower effect are the dominant factors in the cyclical change of the load in the wind turbine.The wind turbulence and wake effect cause asymmetry of the multi-blade load of the rotor.The rotor load transmitted to the other components of wind turbine becomes a periodic excitation force.A significant resonance can occur when the excitation frequency coincides with the natural frequency of the components.2.Establish the wind turbine load model based on dynamicBased on the blade element momentum theory,the load model of the rotor is established.Due to the disadvantage of the theory,the compensation is studied by using the tip-hub loss correction,induction factor correction,dynamic inflow correction and dynamic stall correction.They are introduced to extend the static load model into dynamic load model.According to the material mechanics,the modal calculation method of the rotor and tower is deduced,and the structural dynamics model of the rotor and tower is constructed by modal superposition method.The models of drive train,pitch system and genetator are established with their main dynamic characteristics.The dynamic calculation of the wind turbine is put forward by using discrete numerical calculation method.3.LPV gain scheduling method is proposed to control the wind turbine powerThe influence of complex wind on the power is studied.The rotor inertia and the estimated wind speed are introduced into the pitch control to enhance the output power of the wind turbine to cope with the change of wind speed.The wind turbine is a nonlinear vector system.LPV gain scheduling control method is proposed to control the output power of wind turbine.The LPV gain scheduling control stabilizes the operating trajectory of the wind turbine and the stability of the power output of the wind turbine.4.Study the load control strategy of wind turbine to reduce the fatigue loads of drive train,tower and bladeThe torsional vibration charateristics of the drive train are studied.The Kalman filter is used to estimate the state of the drive train.The generator torque control is used to increase the damping in the drive train.The torsional vibration of the drive train is suppressed.This reduces the fatigue damage of the gear and prolong its fatigue life.The vibration charateristics of tower vibration are studied.The tower has a pneumatic damping effect in forward and backward.The lateral damping is little and it's very easy to occur a significant vibration.Adding the tower damping control into the pitch control and generator torque control to adjust the rotor aerodynamic and generator torque,reduce the tower swing amplitude and enhance the reliability of wind turbine.Study the characteristics of blade load under complex wind conditions and propose an individual pitch control method to reduce fatigue load of blade.The individual pitch control(IPC)regards the load of blades as cyclical and symmetry.The dq coordinate transformation is introduced to control the harmonic components of the load of blades.So the fluctuation of the load is reduced.Aiming at the asymmetric load problem of the rotor,the symmetric component method is introduced.The asymmetric rotor is regarded as a combined system of positive sequence,negative sequence,zero sequence subsystems,which extends the basic independent pitch control and effectively suppresses the wind turbine blades load asymmetry.The IPC based on three kinds of load measurements,under the blade coordinate system,the hub coordinate system and the nacelle coordinate system,are discussed.This can improve the reliability of the individual pitch control system.