The Research Of Wind Turbine Dynamic Model And Pitch Cyclic Control Strategy

Variable speed variable pitch wind turbine has now become the main developmentstream of the wind power due to its advantages of large capacity, efficient wind powerconversion, flexible control and so on. However, it is of great difficulty for variable pitchcontrol of wind turbine because of the unpredictable strength and direction of wind speed.At present, the studies of variable pitch control strategy on the wind turbine at home andabroad are prone to the stability control of wind wheel speed, especially focusing on highwind speed areas. With the increasing unit capacity of wind turbine, new requirements tothe variable pitch control of wind turbine are proposed, such as considering the effect ofthe multiaerodynamic effects of large blade on the wind turbine speed, the capability ofvariable pitch controller on inhabiting system disturbances as well as reducing the fatiguedegree of pitch angle adjustment system, and so on. These have become the hot issues forthe variable pitch control of large wind turbine. The details of this dissertation are asfollows:Through surveying the numerical simulation and analytical methods on theaerodynamic characteristics of variable pitch wind turbine, the direct coupling solution isadopted, which can overcome the defects of large computation and slow convergencewhen using iterative method to solve high dimensional problem during fluid dynamicsmodelling. Practical examples are simulated and calculated by Visual Fortran program.Numerical simulation results show that the computing time using direct coupling solutionis half of that using conventional iterative method, which demonstrates the feasibility andeffectiveness of this method in the aerodynamic characteristics numerical simulation ofwind turbine.The structure features and modelling method of wind turbine are studied. Thenonlinear mathematical model of large wind power system is built by the methodcombining analytical modelling and experimental validation to accurately describe thedynamic process of system drive chain. The wind energy utilization coefficient inmathematic model is obtained by the surface fitting of the experimental sampled data of the wind turbine based on the least square method. A method of identifying and analyzingwind energy utilization coefficient of wind turbine is developed by linearizing the fittingsurface. Theoretical analysis and practical example verification show that the fitted windenergy utilization factor curve is accurate and suitable for modelling and controller designof wind power system under different wind speed conditions.The mathematical modelling and variable pitch control method of wind power systemare studied. Considering the system parameter uncertainties and stochastic winddisturbances, a pitch angle robust controller is designed to achieve speed stable control ofwind power system. The pitch angle robust controller is designed based on the quantitativefeedback theory. Comparing with the conventional PID controller, this method can berealized simply and guarantee the stability and required output power dynamicperformance of wind turbine within the larger wind speed range. Meanwhile, it has goodrobustness to the perturbation of the uncertain parameters in the wind power system.The influence of variable wind speed and multi-aerodynamics on wind turbine isstudied. A loop variable pitch control strategy is proposed to implement speed stablecontrol of wind power system. This control strategy combines quantitative feedback robustcontrol and repetitive control to gain the system speed stable control. The repetitive controlis used to attenuate the periodic speed ripple caused by disturbance, which considers thepartial aerodynamic effects of air-solid coupling model between the wind wheel of windturbine and airflow.