Research On Direct Torque Control For Brushless DC Motor

The brushless DC motor(BLDCM) came into widespread use in industrial production due to its good speed performance, high efficiency, small size, simple structure and low noise. However, because of the great torque ripple, there are limitations in some applications for the demand of high precision conditions. Besides,the position sensor part also having a detrimental effect on the performance of the BLDCM. Aiming at these problems, the direct torque control has been used to control the BLDCM to reduce the torque ripple. And it gets the accurate rotor position of sensorless BLDCM by using the method called zero-crossing method of back EMF.DTC can observe the torque and flux linkage together of the motor, and compares the values in real time with the observed values. Then the control signal is obtained by sending the deviation signal to the hysteresis controller. Finally, based on the flux link and the control signal, choose the proper voltage space vector to control the torque directly.In the DTC control system of BLDCM, as the traditional method, PID can’t realize the parameters on-line control. And BLDCM is a nonlinear system with strong coupling and multi-variable. When the self-adaptive control method was applied to the BLDCM control system, there are some issues on real-time performance and the accuracy. When using the fuzzy control, there is no need to have the precise parameters and the structure of the controlled objects, but the rules of fuzzy control are always set up according to the expertise, there may has some subjectivity. Considered those control algorithms in this paper, the control strategy of multi-index optimization is added into the clonal selection algorithm. It can attain the optimal PID parameters through optimizing the control rules of the fuzzy controller.We choose the MATLAB/Simulink as the simulation platform in this paper, which includes motor module, speed control unit and hysteresis control. The simulation test results showed that the progressed fuzzy controller gets the better performance which has a good rising time, without overshoot and very little steady state deviation; it also has a great effect on reducing the torque ripple effectively.After the simulation, the hardware system of direct torque control of sensorless BLDCM is built based on TMS320F2812 DSP, and the software of the overall systemhas also been presented.