A sensorless position control system by salient-pole brushless DC motor

An error correcting technique of an estimated position angle and rotating speed for the sensorless controlled salient-pole brushless DC motor drives is proposed. An unsymmetrical construction based on the mechanical or magnetic tolerance on the brushless DC motor appears as a modeling error of the motor. This error causes an estimating error which changes periodically. It is difficult to correct the error with hardware like filters. Then, a neuro-like fuzzy technique can he applied to correct the error of the estimated position angle. The position angle is estimated by a new AC current injection method. The errors of the estimated values change periodically, and unexpected cyclic speed errors generate when the motor is controlled as a speed servo system. The fuzzy model which estimates these errors is learned with a back propagation method which uses the cyclic errors as a teacher signal. Then, the system corrects the estimated position angles with the estimated error. The experimental results of the estimated position angle or speed are shown in the paper. From these results, the proposed sensorless control system could estimate more accurate position angle than conventional systems could.