Sensorless starting method for Brushless DC Motors using 180 degree commutation

In this paper a novel technique for determining the back electromotive force (EMF) zero crossing points for 180 degree commutation for Brushless DC (BLDC) Motors is proposed. In 180 degree commutation the motor terminal voltage is exactly the same as the inverter output. Therefore, there is no need for voltage sensors on the machine terminals. In comparison to 120 degree conduction technique, this method makes the advantage of using the machine complete capacity. Based on this new method, a novel sensorless startup technique using 180 degree commutation is proposed. The startup algorithm is based on placing the rotor in a predetermined position. The proposed zero crossing detection and starting methods are simulated and the results show the validity of those two proposed methods. Then a comparison is made between the proposed starting method and the method based on 120 degree commutation. Results show that both the required prepositioning time and the required time to reach the specified speed is less in the proposed method.