The Study Of Doubly Fed Wind Power Control System Based On Mixed H2/h∞ Control Algorithm

Doubly-Fed induction generator is widely used at present. Its control problem has been a concern. This paper analyzes the system structure and the working principle of the DFIG, and divides it into two parts to study: mechanical part and generator part. Based on the wind energy absorption principle, mechanical transmission mechanism and motion equation, the mathematical model of mechanical part is established; by using coordinate transformation and stator flux orientation in the two-phase synchronous rotating turn coordinate, the mathematical model of the induction generator is established. In order to study of the influence of wind speed near rated value to DFIG system in the time of the DFIG run at rated conditions, the DFIG third order linear mathematical model with small disturbance is established by use of small signal analysis, and is expressed by the form of the equation of state. By analyzing the stability of the model, the stability condition is granted, and the influence of wind speed on the control system is illustrated though simulation based on actual engineering parameters. According to the different state, the DFIG is divided into four running region, and appropriate control strategy is proposed, the pitch angle control and the doubly fed induction generator control cooperate with each other to complete the whole control task. The pitch angle uses traditional PID control method, by adjusting the pitch angle makes the wind wheel speed to the rated value, PID pitch angle controller is designed, and the stability condition is given. Concerning the influence of wind speed, H2/H∞ control method is proposed, and the DFIG control problem is converted to mixed H2/H∞ control problem, the DFIG state feedback controller is designed based on H2/H∞ control algorithm by solving the Riccati equation, in order to reduce or eliminate adverse effects of the ranged wind speed to DFIG system in rated condition, and the stability conditions is given. The simulation results show that the mixed H2/H∞ control algorithm solves transient oscillation problem caused by the wind disturbance, improves the robustness of the system, improves the performance of the system.