Sensorless Control Method for Single-Phase BLDC Motors Based on Phase Current Information

This paper proposes a new low-cost sensorless control scheme for the commutation of single-phase brushless direct current (BLDC) motors. For this method, the phase current information is observed and analyzed to determine the instance of triggering the commutation of the motor. The control method is based on investigating the effect of the back-electromotive force (back-EMF) on the shape of the phase current using the motor model equation. An upward inflection point is observed in the phase current waveform, which coincides with the downward inflection point in the back-EMF. After the inflection point, the phase current is observed again until the difference between the phase current and the magnitude at the aforementioned inflection point exceeds the set threshold. Once this threshold has been reached, motor commutation is triggered. Experimental verification of the proposed scheme was done with a four-pole, single-phase axial fan with improved performance compared to sensored control using a Hall-effect sensor.