Research On Several Control Problems For Doubly-Fed Variable-Speed Constant-Frequency Wind Power Systems

As the world energy crisis and environmental pollution problems have become increasingly prominent, the new energy strategy emerges to search for clean and efficient renewable energy. The wind power has attracted great attention as a class of clean and rich renewable energy, and the wind power industry develops rapidly in the world. Many countries promote the development of native wind power technology through legislation or policy support. With the rapid development of Chinese economy, the requirement of electric power is getting more and more. As an energy consuming country, China has widespread lack of electricity in recent years. Power shortage and unreasonable power structure have begun to influence Chinese all-round development. With very rich wind power resource, China needs to research and develop wind power technology, which has important strategic significance.Based on input-ouput feedback linearization method and Hamiltonian con-trol theory, this paper investigates the maximum wind power tracking control and H∞control for doubly-fed variable-speed constant-frequency(VSCF) wind power systems. Firstly, this paper introduces the background, the significance and the research status for wind power systems. Secondly, the basic principle and structure of wind power systems are generalized, which includes aeroturbine operation char-acteristics, working principle, system model and variable-speed constant-frequency theory, etc. Finally, two maximum wind power tracking controllers and an H∞controller are desigened for a class of doubly-fed VSCF wind power systems. The main contents of this paper are as follows:(Ⅰ) Maximum wind power tracking control design for doubly-fed VSCF wind power systemsIn this section, the maximum wind power tracking control design is inves-tigated for doubly-fed VSCF wind power systems. Firstly, a rotor excitation controller is designed for wind power systems using both the stator field-oriented vector transformation technique and input-output feedback linearization method, which can realize asymptotic tracking control of the wind turbine speed and re-active power. With the controller, a maximum wind power tracking controller is proposed for the wind power systems by the optimal tip-speed ratio technique and power distribution relationship. Based on prefeedback dissipative Hamilto-nian realization and Embedding control method, a rotor excitation controller is then provided for a class of wind power systems to work at the desired point given, which can obtain the asymptotic tracking control of the wind turbine speed and reactive power. Based on this, the maximum wind power tracking controller is obtained via the optimal tip speed ratio technique and power distribution rela-tionship. Finally, numerical simulations verify the effectiveness of the controllers provided in this section.(Ⅱ) H∞control design for doubly-fed VSCF wind power systemsIn this section, H∞control design is studied for affine nonlinear systems and doubly-fed VSCF wind power systems. Firstly, with twice orthogonal decomposi-tion, an H∞controller is designed for a class of affine nonlinear systems. When external disturbances vanish the closed-loop systems are asymptotically stable, while the L2 gain of the affine nonlinear systems is limited with external distur-bances. Based on the input-output feedback linearization method, an H∞control is then proposed for the doubly-fed VSCF wind power systems by solving Riccati equation. The controller can enhance the robustness of wind power systems with external disturbances. Finally, study of examples with simulations shows that the controllers obtained work very well.