The improvement of performance at low speed by offset compensation of stator voltage in sensorless vector controlled induction machines

The speed range for sensorless vector controlled induction 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. This paper presents a method of improving the low speed performance of sensorless vector controlled induction machine drives by offset compensation of the stator voltage. The offset is compensated by using the fluctuation of the estimated rotor flux. The validity of the proposed method is verified by experimentation.