Research Of Direct Torque Control Strategy Applied To Doubly Fed Induction Generator In Wind Power Generating System

As the world's fossil energy scarcity and increasingly severe environmental pollution, wind energy, as a kind of renewable green energy, is paid more and more attention during lots of countries in the world. In order to make wind energy more effective and improve the level of wind power, this dissertation on direct torque control strategy applied to doubly fed induction generator in wind power generating system is analyzed. The main contents are as follows:Firstly, the current level of wind power is described in the dissertation, introduces the unique advantages of doubly fed induction generator in variable speed constant frequency (VSCF) wind power generation system, particularly analyzes the advantage of the direct torque control compare with traditional of vector control is used in doubly fed induction generator.Secondly, a mathematical model of wind turbine and its simulation are established, obtaining curve between the relationship of the wind turbine output mechanical power and speed in different wind conditions. All these provide a demonstration basis for the final simulation of the entire system. In the dissertation, using the proportional control to replace the complicated PI or PID methods to control the wind turbine pitch, overcoming the defects of pitch institutions movements frequently and low effect, and more conducive to maximum power tracking, improving the efficiency of wind power.Thirdly, in the dissertation analyze basic principles of the doubly fed induction generator and establish the mathematical model.Then in the thesis analyze the basic principles of direct torque control with doubly fed induction generator, and build a block diagram of direct torque control strategy using in VSCF doubly fed wind power generation system. In this process, using nearly circular paper of the space voltage vector flux to replace the traditional hexagonal space voltage vector flux, which is more effective in reducing the torque ripple and content of current Harmonic. In addition, the dissertation adopted the Schmidt three-point torque regulator to replace the traditional two-point torque regulator,which is more detailed analysis of the deviation of torque and improving the performance level of the whole system.Fourthly, in the thesis, we analyze the double PWM converter structure and function, emphatically analyze the functions of the grid side of the converter, and using the software of MATLAB/simulink simulate the grid side of the converter in grid voltage keep in constant and changes on simulation analysis. The results demonstrate that in the condition of grid voltage keeping in the constant, wind power generation system can operate in steady. When the grid voltage mutation, wind power generation system will produce fluctuation instan-taneous, but it returned to normal soon. Finally, using the software of MATLAB/simulink simulate the entire system in the two case of grid voltage in constant and mutation. Simulation results test and verify the methods of direct torque control work in the doubly fed induction generator of VSCF run in stable, the effect of adjusting the speed well, little torque ripple, etc., thus these can ensure that the wind power system use the wind energy more effective.