Sensorless vector controlled induction machine drives with fast stator voltage offset compensation

This paper presents a method for improving the performance at low speed of sensorless vector controlled induction machines. The speed range for such machine drives is limited to about 1:100 in industry. The main reason for this limitation is inaccuracy of stator voltage regulation. The lower the motor speed becomes, the lower the stator voltage becomes. Therefore, it is difficult to regulate or measure the stator voltage precisely at low speed, and difficult to control motor speed and motor torque precisely. The authors have proposed a method of improving the low speed performance of sensorless vector controlled induction machine drives by offset compensation of the stator voltage. However, the method needs a lot of time to estimate the DC offset value included in the measured stator voltage. In this paper, a modified offset compensation algorithm is proposed. The newly proposed method needs only a few cycles to estimate it.