A Closed-Loop Starting Method of Sensorless Brushless DC Motor

The sensorless brushless DC motor has broad application prospects, but the sensorless control method of commutation by detecting the motor back electromotive force (EMF) is not suitable for low speed conditions, making it difficult to start stably and reliably. This paper analyzes the change of DC bus current when the control system delays switching sectors, and obtains the motor commutation timing by detecting the current change rate. A closed-loop speed control system for the starting process of sensorless brushless DC motor is designed, and the three stages of the starting process is analyzed. Finally, the designed control system has been experimentally verified that the brushless DC motor can be started reliably.