Abstract: Brushless dc motors are getting more attention in many areas owing to its compactness, maintenance, high efficiency and low cost. Precise detection of rotor position is essential to achieve high efficiency. Mechanical sensor based methods increase size and inaccuracy. Back EMF method is one of the most popular control method for sensorless brushless dc motor. But this method is not suitable for high-speed operation, for the pulse width of zero-vector may be very short. Z-source inverter based approach to zero-crossing point detections during the shoot-through vectors for sensorless brushless dc motor is discussed here. This approach separates the zero crossing point detections from speed adjustment, and makes the shoot-through vector not influence the motor speed-adjustment directly. With this approach, the sensorless drive can operate in a wide speed range. It not only provides boost voltage for sensorless brushless dc motor drive system, but also improves the utilization rate of dc source voltage and the safety of the drive system.
Keywords: Brushless dc motor, sensorless, zero-crossing point detection, Z-source inverter