Research On Fuzzy Control Technology Of Doubly-fed Wind Power System

With the overuse of petroleum energy sources, environment depravation and the worsening of power supply circumstance problems increasingly, it is provided with very important meanings to solve energy shortage and environment depravation by using wind energy as the one of the most important clear substituted energy source in the future. The Variable-Speed Constant-Frequency(VSCF) wind energy generation system runs in a wide speed range, energy can flow in double direction, and its transducer possesses the characteristics of small cubage, light weight and low cost. So the VSCF double fed wind energy generation system used in the wind energy generation system widely are becoming more and more important.The two-level source back-to-back PWM converter is used in this thesis. The VSCF wind-power system with doubly-fed induction generator is commonly controlled with PI controller which depends on the parameters of system. The change of generator parameters and the speed of wind has an effect on the control effect. The fuzzy control is used to control the doubly-fed wind-power system in order to improve the robust of the system.In the research of the grid-side PWM converter, in this thesis a novel control strategy is designed combined PID with fuzzy control and feed-forward of load current which is applied to optimize PWM rectify system. The simulation results demonstrate that this control strategy is convenient and efficient. Based on the analysis of the mathematical model of PWM rectifier and the characteristics of the unbalanced grid, a new dual closeloop controller of the three-phases rectifier is proposed to overcome the shortcomings of the traditional three-phases rectifier that there is the second harmonic power in the DC side when the grid voltages are unbalanced. The fuzzy PI control is used for the voltage outerloop to improve the speed of dynamic response. The respective control of the positive and negative sequence currents are used for the current interloop without the sequence current decomposition. The simulation results suggest that the proposed controller could adjust the DC voltage steady quickly, decrease the harmonic power and improve the dynamic performance of the rectifier under the unbalanced grid voltage conditionAs for the rotor-side PWM converter, the vector transform based on stator-flux-oriented is used to simplify the model of DFIG. The fuzzy control is used to realize idle load grid-connection control. The simulation results come to a conclusion that fuzzy-control has good robustness and applicability in the idle load grid-connection control. The principle of the maximum wind energy tracking is investigated deeply. A grid-voltage-oriented vector controller of DFIG is designed, which can make the system capture the maximum wind energy and decouple the active and the reactive power. The theory analysis and simulation results demonstrate this control strategy is convenient and efficient.