Approach to Zero Crossing Point Detection of Back EMF 

Based on the Z-source inverter, this paper proposed a novel approach to zero-crossing point (ZCP) detections during the shoot-through vectors for sensorless brushless dc motor (BLDCM). The proposed approach separates the ZCP detections from speed adjustment, and makes the shoot-through vector not influence the motor speed-adjustment directly, while the zero-vectors and active-vectors are used exclusively to adjust the speed of BLDCM. With the proposed approach, the sensorless BLDCM can operate in a wide speed range without switching the detection points and the reference levels, and it is unnecessary to change the reference levels according to the PWM technique.

The terminal voltages limited by diode can be directly compared with the reference zero level during the shoot-through vectors, so as to reduce the detection error caused by attenuation. Moreover, Z-source inverter not only provides boost voltage for sensorless BLDCM drive system, but also improves the utilization rate of dc source voltage and the safety of the drive system. In addition, this paper analyzed the terminal voltages of the floating phase during each vector. The experimental results verified the correctness of above theories and proved the effectiveness of the proposed approach.