Optimal Speed Tracking Control For Doubly-fed Induction Generator

Energy shortage and environmental pollution are becoming more and more serious problems. The wind energy is a kind of clean green renewable energy, so it can effectively solve the urgent problems of energy and environment by developing and utilizing wind energy. Therefore, this thesis treats the doubly-fed induction generator as the research object, and a speed control system which can mostly acquire the wind power and enhance the efficiency of transformation of the wind power is designed.Firstly, the structure and control method of the doubly-fed induction generator system is analyzed; the essential characteristics of wind turbine and the maximum wind energy capturing method are researched; the mathematical functions of doubly-fed induction generator in the three-phase stationary ABC coordinate system and two-phase synchronously rotating d-q coordinate system are discussed. The state space description of doubly-fed induction generator is derived, and the control issue is formed.Secondly, for it is difficult to obtain the ideal reference value for the controller during the wind speed changes, this thesis builds a net identification model of the optimal angular velocity for the doubly-fed induction generator by using dynamic fuzzy neural network when the wind speed is below the rated speed. The most important feature of the network's learning algorithm is, at the same time, that the parameters and the structure of the networks are adjusted, and its learning speed is very fast. Through training, the network model can quickly get the optimal angular velocity under which the unit will operate during the wind speed changes, and can provide a useful reference to develop appropriate control strategies. Simulation results show the validity and effectiveness of the model.Finally, aiming at capturing maximum power for the turbine when the wind speed is below the rated wind speed, a switching "optimal" tracking controller of the generator angular velocity is designed. The optimal tracking controller of generator angular velocity is designed by using different system parameters in different angular velocity ranges in the light of switching control. When the generator is running under a certain velocity range, the controller will switch to the corresponding controller designed under the certain velocity parameters. The control idea is by controlling the voltage of the generator rotor to adjust the generator angular velocity to track the optimal angular velocity. The simulation results show that the controller designed can well track the optimal angular velocity, and make the systems have good dynamic and static characteristics. And also the controller can realize maximum wind energy capture and increase efficiency of wind power conversion. It should be significant for the operation control of the actual system.