Precise speed control of the PM brushless DC motor for sensorless drives

This paper describes the method of precise speed control for the sensorless PM BLDC motor drives using the PLL. The method using the third harmonic voltage component between the networking resister of the stator phase voltage and the motor neutral point is applied for the sensorless PM BLDC motor drives. As a result, we obtained that it results of achieving a good performance over a wide speed range because it is not sensitive to the filtering delays. In addition to the estimated Hall-ICs signal circuit by the Johnson counter, the estimated Hall-ICs signal haves the identical period and frequency like sticked Hall-ICs signal in the PM BLDC motor. Also, we proposed the rotor position signal synthesizer using the PLL based 6-pulse. Because of high resolution obtained by using the PLL circuit, we can improve the wide range of speed response characteristic more exactly. Some experimental results are provided to demonstrate the validity of the proposed control method.