Improvement of torque-speed characteristics of brushless motor by automatic lead angle adjustment

The torque-speed characteristics of a brushless motor vary depending on the lead angle (commutation advance angle). Moreover, the lead angle maximizing the torque varies depending on the speed, and this makes it necessary to change the lead angle in accordance with the speed, to obtain favorable torque-speed characteristics over the entire speed range. This corresponds to changing the installed position of the Hall elements with the speed, but it is practically impossible to do so. We proposed a method of substantially changing the lead angle in accordance with the speed, by changing the phase of the output voltage from the Hall element together with the speed, instead of moving the Hall element. We also made it clear that a problem in the realization of this method is the distortion of the output voltage from the Hall element, and examined countermeasures against it. Moreover, observation was made of the torque-speed characteristics obtained by this method.