Self-correction Commutation Method of Position Sensorless BLDCM Using Back-EMF Adaptive Threshold Voltage Comparison Circuit

The back electromotive force (back-EMF) method, based on detecting zero-crossing points of back-EMF, is a widely used technique for sensorless brushless DC Motor. However, the commutation error caused by LPF along with hardware and software implementation results in torque deterioration and efficiency reduction. This paper explores an optimized back-EMF method, which owns the capacity of commutation error self-correction. First, a back-EMF threshold comparison circuit is proposed for commutation signal acquisition, which can adjust the commutation phase by an offset voltage. Then, a hardware-based regulator is designed to provide an auto-adjusted offset voltage for achieving the accurate commutation. Compared to the conventional method, it can achieve the realtime corrected commutation automatically without using digital processor and overcome the sampling speed limitation due to using a hardware-based closed-loop regulation. Experimental results on a magnetically suspended control moment gyroscope prototype verify the proposed method.