Variable-speed Constant-frequency Doubly-fed Induction Generator Control Strategy Research

In recent years, energy crisis and the greenhouse effect have become important issues all over the world. To develop and utilize new energy is the fundamental way to solve the above problems. Wind power has become one of the world's fastest growing new energies. Variable speed constant frequency (VSCF) double-fed induction generator (DFIG) not only greatly broadens the range of speed in cutting-in process, more importantly, but also achieve maximum power point tracking (MPPT). DFIG improves the stability of the grid and has become the mainstream. Control technology is the core of wind power utilization. DFIG's parameters are easily affected by many factors and it will degenerate the control performance. This paper focuses on DFIG cutting-in control, operating control, as well as the influence of parameters perturbation to both cutting-in control and operating control.Vector control strategy based on flux-oriented has been widely used in the field of speed control technology of A.C. drive. As the control subject of VSCF-DFIG is Doubly-fed Induction Generator, vector control is quickly spreading to wind turbine technology. In fact, vector control is a decoupling way. It is reasonable to adapt vector control method in active-reactive power decoupling control.Using stator flux-oriented vector control method, the paper respectively deduced the no-load cutting-in control strategy and active-reactive power decoupling control strategy. As for cutting-in control strategy, it designed DFIG open loop cutting-in control algorithm and the double closed loops control algorithm based on voltage-current feedback. As for power decoupling control strategy, it designed both DFIG active-reactive power decoupling open-loop control algorithm and double closed loops control algorithm based on power-current feedback. The paper studied the MPPT control strategy on the basis of wind turbine analysis. Also, taking the sensibility of vector control into account, it rightly deduced the mathematical expressions showing the exact influence of parameters perturbation on DFIG cutting-in control and for the first time researched the influence of parameters perturbation on DFIG output power.On MATLAB7.0/SIMULINK platform, simulation models were set up to testify the algorithms the paper designed. The simulation results show that the control algorithms designed are effective and lay a theoretical foundation for the implementation of control strategies. The analysis on parameters perturbation of DFIG provides theoretical proof for the disturbance rejection control research.