Research Of Control Theory Of DFIG Variable-speed Wind Turbine

With attachment importance to energy source scarcity and environment pollution, the wind electric power generation has developed dramatically around the world. How to enhance unit capacity and operation effectively becomes important matter of the wind electric power generation.Variable-speed constant-frequency (VSCF) operation is a new highly efficient technology for power generation, which has a good future in the field of wind power generating. In this paper, several schemes of VSCF are compared firstly, of which gets doubly-fed generating mode. Doubly-fed VSCF wind power generating system uses a doubly-fed induction generator, which rotating speed can be changed according to wind speed, and it ensures a constant-frequency output by controlling the frequency of current input to rotor windings. Among the various wind generation systems, variable speed constant frequency doubly-fed induction generator (DFIG) becomes mainstreamed for its advantages.By making use of simulation experiment, this paper has also carried out detailed analysis and research of the vibration problem of permanent magnet synchronous generator. The immanent cause of producing vibration for synchronous generator is found out.According to systematic analysis of the principle of wind turbine, simulating models of wind speed and wind turbine are given. After running of the models, the power, torque and turbine speed curves of wind turbine on variable wind speed are given out and analyzed.After analyzing the mathematical model of wind turbine and doubly-fed induction generator, schemes of the power flow between wind turbine and generator are given. A static equivalent circuit is also shown. Through the reference frame transformation, the electromagnetic equation, dynamic equivalent circuit, and vector graph of doubly-fed generator can be gotten in the d-q reference frame. Furthermore, under the vector control strategy of stator field-orient, a vector control model is derived from the generator,and a close loop control system is built accordingly. By using vector control strategy, the control of stator active power and the reactive power can be essentially decoupled.