Research on filters for back EMF zero-crossing detecting in sensorless BLDC motor drives

In sensorless operation of brushless DC motor drives, a typical method called "back EMF method", is sampled to detect the induced EMF zero-crossing of the unexcited winding. The filters are used to eliminate high frequency components of the terminal voltages and to extract back EMF of the motor. In this paper, FFT analyses of terminal voltage contents of the BLDC motor are presented. The principles of filters are introduced, and two kinds of filters, a passive band-pass filter and an active low-pass filter, are designed for BLDC motor drives. The study shows that the theoretical analysis is coincide with that of the experiments