Application Research Of Nonlinear Control Theory In Wind Power Control System

Variable speed constant frequency (VSCF) wind turbine using Double-fed induction generator (DFIG) has become an advanced research hotspot in the aspect of wind power, because it can run in a variable speed within a relatively wide range of wind speed, has the stronger wind power capturing capability and can realize the decoupling control of active and reactive power. Supported by the ministry of education key project (NO:105049) and the national natural science fund project (NO:50677021), this thesis mainly studied the power control of AC excited generator and the pitch angle control of wind turbine according to the characters of wind power system itself. The primary contents and research results are as follows:(1) Brief reviews of the control techniques for wind power system and the development of nonlinear control theory research are given.(2) The mathematical models of wind power system and AC excited generator are established. Nonlinear state equations are derived and are transformed to affine nonlinear forms.(3) By comprehensive use of exact linearization theory of nonlinear system and internal model control method based on H∞ptimization criterion, the power tracking robust control law of AC excited generator is designed. The simulation results show that this method can realize the completely decoupling control of active power and reactive power, has satisfactory tracking effect and dynamic and static characteristics, and has better robustness to model uncertainty and external disturbance.(4) Due to the wide range and frequent change of wind speed, the operation point of system is usually in constant variation. Corresponding to this characteristic, the pitch angle controller is designed based on nonlinear dynamic inverse method. The simulation shows that when the operation point changed widely, the control system still has better control effect, and this method can overcome the shortcomings of local domain approximate linearization method, furthermore, it has relatively simple solution process.(5) In order to reduce the bad influence of wind disturbance, a pitch angle control method based on nonlinear disturbance attenuation theory is proposed. The simulation shows that this method has good inhibitory effect to the wind turbulence, adapts to the large range variety of operation point and can realize the steady power output above the rated wind speed.