The Research Of Brushless Doubly-fed Machine And Direct Torque Control System

Brushless doubly-fed machine (BDFM) is a new kind of special machine in the electrical drive field. The different operating mode of BDFM can be modified by adjusting the frequency, amplitude value of the voltage in the stator control winding. Compared with induction motor, the BDFM can reduce the rating of the inverter; compared with double fed induction machine, the BDFM can enhance the system reliability and leave out the slip ring and the brush. Because of these advantages of BDFM, this machine is very suitable for high-capacity variable frequency adjustable speed drives and adjustable speed constant frequency generator. It is very significant to research the control strategy for BDFM and put it into practice.In this paper, systematic basic structure and mathematics model on BDFM is carried out. The frequency of every winding is converted to the same value by using frequency-conversion method. Then the BDFM state equations are given . this paper presents the BDFM's the circuit network model and the rotor reference frame d-q model by derivating the BDFM's mathematic model . The parameter calculating method of different mathematics model is dissimilar. In this paper, different method on BDFM is carried out.On the fundament of analyzing BDFM's principle and the direct torque control method, a control method of BDFM is presented. To reduce the torque ripple of Brushless Doubly-Fed Machine based on conventional direct torque control(DTC), this paper proposes a new control strategy - torque predict. The simulation shows that torque predict can reduce the torque ripple, improve the current waveform of stator . This system also has good dynamic and static performance. Base on learning the hardware structure of LF2407A and how to program, the program is designed and writed to generate the DTC and other modules. Had completed the software design of variable frequency variable speed system of brushless doubly-fed machine.The paper draws some innovative and significant conclusions by reasonable analyzing,computer simulating and experimental testifying combined with the prototype,which offer some technical foundations for the farther practical research of BDFM and its control system.