An Approach to Position Sensorless Control System for Brushless DC Motor

This paper describes a control system of sensorless brushless DC(BLDC) motor. Firstly, the back-EMF is adopted to detect rotor position. Secondly, the back-EMF is very small in the motor starting process, and it is difficult to obtain rotor position efficiently. A re-setting method of the rotor is proposed in the paper, and current closed loop is used for high-speed and safety in the motor starting process. Finally, a good speed and current double closed loops system is designed. The current commutation and motor speed withdraw problem without the position sensor is discussed in details. The experimental results have shown the validity of the sensorless control system and the accuracy of the detective position signal obtained from a prototype BLDC motor of 400 W rating.