The Direct Torque Control Of Brushless DC Motor Based On Position Sensorless Control Method

Permanent magnet brushless DC motors (BLDCM) have been more and more widely used in industry applications because of their advantages such as higher ratio of power to volume, lower noise and easier maintenance compared to permanent magnet DC servo motors. However, the existence of rotor position sensor makes the application of BLDCM in some area impossible. In addition, because of various reasons, the torque ripple generated by BLDCM is inevitable. So, the position sensorless control method and the torque ripple prohibit scheme become the focus of BLDCM and researched by a lot of researcher.The direct torque control (DTC) is a high performance control method which proposed in 80s, last century, in AC motor speed control area. This method has a lot of advantages such as simple control structure, good dynamic and static performance, rapid torque response and strong robust. The DTC observes the fluxlink and torque of the motor in the stator coordinate, and compares the observed values with the set values to obtain the error. And then the control signal is obtained by inputting the error to the controller. Finally, with this control signal and the state of fluxlink, the corresponding voltage space vector is selected, so that the torque can be controlled directly. Actually, the DTC is a torque feedback control method that can control the torque well and rapidly, which make the DTC a very prospective method to prohibit the torque ripple of BLDCM. So in this paper, the DTC is used to control the BLDCM, in the purpose of reducing the torque ripple.Besides, in this paper, the research about the application of DTC in BLDCM under the position sensorless control method is did, in order to decrease the torque ripple of BLDCM which controlled by the position sensorless control method. And then the back electromotive force (BEF) method is used to perform the complex control of DTC and position sensorless control. But the BEF method can not start up the motor. To solve this problem, on the base of the work did by other people, a improved start method combined with the DTC is proposed in this paper, so that the motor can start up successfully.Finally, the BLDCM hardware control system based on the MSP430F149 MCU is introduced. And the experiment is carried out in this system, and then the experiment result is given.