Sensorless Control of Single-Phase BLDC Motors based on the Improved Winding Time-Sharing Method

Low-cost sensorless control systems for single-phase brushless direct current (BLDC) motors usually use the winding time-sharing method as the main control method. This method accomplishes commutation by detecting the zero crossing point (ZCP) of back-electromotive force (back-EMF). The key is how to accurately control the time to turn off the power transistors in advance. Turning off too early reduces phase current utilization, while too late may result in motor commutation failure. To solve the problem that the optimal turn-off time is difficult to determine, this paper proposes an improved winding time-sharing method. First, a simple function is built to pre-estimate the time to turn off the power transistors early at different speeds. To ensure that the system can detect the ZCP of back-EMF to complete the commutation. Secondly, the actual speed of the motor is estimated by detecting the time between the turn-off point and the ZCP of back-EMF. And adjust the turn-off time to the best according to the speed change. Maximizes the electromagnetic torque and output power of the motor while completing the commutation. Finally, the experimental results show that the control method can adaptively adjust the power transistors turn-off time to optimize the motor speed while realizing sensorless control, and the feasibility of engineering applications is higher.