Position sensorless commutation method of coreless BLDC motor based on synchronous frequency extraction algorithm

In this paper, a position sensorless commutation method without phase shift is proposed for brushless DC motor (BLDCM). First, the unexcited phase back electromotive force (back-EMF) is reconstructed through a multiplexer, and the fundamental wave signal of reconstructed unexcited phase back-EMF is obtained through a synchronous frequency extraction algorithm. Then, the accurate zero-crossing points (ZCPs) of the extracted fundamental wave signal are obtained via detecting the fundamental waveform crossing zero point. Because there is no phase shift on the ZCPs, the BLDCM can achieve high accurate commutation, which improves the system efficiency.