Wind Turbine Tip Speed Ratio Cascade Control With Unmodeled Dynamic Compensation At Low Wind Speed

Maximum Power Point Tracking(MPPT)method is proposed to achieve maximum capture of wind energy at low wind speeds of wind turbines.Due to the emergence of high-power wind turbines,the original MPPT method resulted in a significant reduction of wind energy capture efficiency of high-power wind turbines.The reason is that highpower wind turbines have new features of drivetrain flexibility and high inertia.The Tip Speed Ratio method is a typical representative of the MPPT method due to its advantages of high capture efficiency of wind energy.It is difficult for the current Tip Speed Ratio method to obtain the ideal effect on the actual system.Either because of the over-reliance on the mathematical model,or the dynamics of the tip speed ratio without the consideration of the new features of high power wind turbines.Thus,the current Tip Speed Ratio method cannot greatly improve the wind power capture efficiency of high power wind turbines.In addition,there is a contradictory between improving efficiency and smoothing power with existing improved MPPT method.In view of the above problems,under the support of fund for the research of data-driven wind turbine operation feedback control,this thesis presents the tip speed ratio cascade control method with unmodeled dynamic compensation for high power wind turbines,which are of the characteristics of comprehensive complexity,such as large inertia,drivetrain flexibility and unknown model parameters.The main works are as follows:(1)Aiming at the shortcomings that the control effects of some tip speed ratio methods are dependent on the mathematical model,this thesis transforms the two-mass model of wind turbines into a system model consisting of second-order linear models and higherorder nonlinear terms.In order to achieve the tracking performance of rotor speed,the model-based and data-based idea is proposed to design a PID speed controller with unmodeled dynamic compensation for inner loop,which avoids control method’s overreliance on mathematical model.(2)In view of the problem that the wind energy capture efficiency is reduced due to the large inertia of the wind turbine,tip speed ratio PI controller is adopted on the outer loop to achieve optimal tip speed ratio tracking,which shortens the tracking dynamic process of optimal tip speed ratio.(3)Aiming at the fluctuation of wind power output caused by strong wind speed disturbance,this thesis designed a fuzzy inference system to optimize the speed setpoint.The system is based on the current speed tracking state of the system and the limited response capability of the mechanical system.The fuzzy inference system solves the conflict between improving efficiency and smoothing power.(4)In order to verify the validity of the algorithm,this thesis compared the proposed method with several existing methods by simulation experiments.Simulation experiments include numerical comparative simulation with CART wind turbine model and FAST(Fatigue,Aerodynamic,Structures,and Turbulence)comprehensive software simulation comparative experiment with NREL 5MW wind turbine model.The experimental results show that the proposed method can not only improve the wind energy capture efficiency but also keep the power smooth and the mechanical load low,and fully demonstrates the effectiveness of the proposed method.