A Novel Starting Method for Sensorless Brushless DC Motor with Low Cost

This paper presents a novel method to improve the starting performance for sensorless brushless DC motor (BLDCM) with low cost, based on the principle of back electromotive force (BEMF). The commutation points are extracted from three phase terminal voltages achieved by AD converters integrated in the microprocessor. The phase delay caused by the detection circuit is compensated. The start process consists of alignment, accelerating, and switching. In the accelerating process, the commutation instants are determined by the zero-crossing points and phase delay table. The motor can be started reliably because of the closed-loop startup strategy. Experimental results have verified the effectiveness of the proposed method.