The Study On The Control Of Double-Fed Variable-Speed Constant-Frequency Induction Generator

Wind power is clean and non-polluting energy, its technology is more mature, the most suitable for large-scale development. From our country and other country’s current situation and prospects of wind power, the installed capacity and generating capacity is growing, the wind power is developing in the new direction of increasing single-machine capacity, offshore wind, bus monitoring in wind farm and low voltage ride through. The control technology has undergone development from fixed pitch to variable pitch, from constant speed constant frequency (CSCF) to variable speed constant frequency (VSCF).With the development of power electronics and the problem exposed from the traditional control methods, in recent years, the new control method of converter has been applied, including the variable structure of sliding model, intelligent control and inverse system control method Etc.Firstly this paper analyzes the mathematical model of DFIG, through the requirement of the converter of DFIG, the AC-AC converter, Matrix AC-AC converter, dual PWM converter are compared. The dual PWM converter is sure to be used, and then the working principle of DFIG working in VSCF and energy flow in different conditions is studied.Against the dynamic stability’s deficiency of the vector control strategy of gird voltage-oriented when the system parameter changes.On the basis of the mathematical model of grid-side converter,by analyzing the principle of the inverse system and the variable structure of sliding model,this paper establishes the mathematical model of the current inner-loop control based on inverse system and the voltage outer-loop control based on the variable structure of sliding model.Through the software of Matlab/simulink,the simulated waveforms in two control method are compared when the operation is normal, the load changes, and the voltage drops, the simulation and experiment verify the feasibility and superiority of this method.To the modulated method of the PWM converter,the Space Vector PWM is used and the method of applying DSP is studied.Then the working principle of wind turbine and operational characteristics are introduced, the principle of capturing the maximum power is studied. On the basis of the mathematical model of DFIG, the vector control strategy of stator flux-oriented is established, and the structure of the power outer-loop and the current, voltage inner-loop is determined. By simulating the system, the decoupling of the active, reactive power and capturing maximum power is achieved. When the grid voltage is unbalanced in the traditional vector control strategy of stator flux-oriented, the active power, reactive power of stator side and the electromagnetic torque have2octave pulses. So this paper proposes the double dq, PI current loop control of the motor in the stator voltage-oriented can eliminate the2octave pulses, the simulation results verify the feasibility of this method.Finally, the wind power experimental simulation system is founded, this system takes the single DSP controlling back-to-back PWM converter as the core,the auxiliary systems contain the Simmens’DC speed controlling DC motor to simulate the wind velocity,PLC controlling the main circuit on and off,PC used in the unit of monitoring and management.The PC monitoring interface based on the Schneider configuration software CITECTSCADA7.10is designed.By setting up the case of basic wind, progressive wind and gust, the experimental waveforms are achieved, it verifies that the inverse system and the variable structure of sliding model can achieve the goal the grid-side converter,the vector control strategy of stator flux-oriented can achieve the goal of the machine-side converter.