| As a kind of clean and renewable green energy, the wind energy resource is an effective solution of global energy tension and pollution of natural environment problems.The correlative wind power generation technology has been attracting more and more attention worldwide.For its high efficiency and practicability, the variable speed constant frequency (VSCF) wind power generation technology has the vast potential for future development.VSCF wind power generation system with doubly-fed induction generator (DFIG) is the object of study in this paper. DFIG is the core of this system. After analyzing its work principle and operating characteristic, the coordinate transforma-tions with power and number of turns of winding invariance constraint conditions are discussed respectively. The mathematical models of DFIG both in three-phase stationary reference frame and in d-q synchronized rotating reference frame are deduced in detail.The steady-state equivalent circuit and power flow process of the machine are also studied in the paper.Wind turbine is the important component of the wind power generation system which transforms wind energy into mechanical energy. Based on the theory of wind, running mechanisms about wind and wind turbine system are studied, and each relevant mathematical model of them is built. The quantity relationship among output power of wind turbine, rotate speed, wind velocity, tip-speed ratio and rotor power coefficient are discussed detailedly, and the maximum wind energy tracking control strategy is also deliberated. To realize the decoupling control of active power and reactive power of VSCF wind energy generation system and its maximum wind energy tracking in rated wind speed range, the stator flux oriented vector control system is presented and designed in the paper, and both of them are splendidly completed.The converter is key component of system to make the wind power generation system able to operate in VSCF mode.On the basis of serious analysis on main circuit configuration, operating principle, the cosine wave crossing and triggering control principles of the converter, its output voltage harmonic is studied. Then the influence of various situations and parameters to the output voltage harmonic characteristics is analyzed. The harmonic calculation method of VSCF wind power generation system is deduced with DFIG harmonic equivalent circuit model.The system harmonic characteristics, the influence of harmonic to system and harmonic restraining measures are also briefly described in this paper.Finally, simulation models of each part of the VSCF wind power generation system are built by the software MATLAB and the simulation experiments are performed. The simulation results validate the correctness of the simulation models. The paper has done all-around study on VSCF wind power generation system from theory to simulation, which has some applicable reference value for correlational research and has established stability theoretical foundation for future study work.
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