Robust control against rotor resistance variation for speed sensorless induction motors

In this paper, a new speed sensorless induction motor scheme which can estimate rotor speed and rotor resistance simultaneously is described. The rotor flux reference is given as sinusoidal waveform to conduct on-line simultaneous estimation of the rotor speed and the rotor resistance without affecting precise torque control. The estimation can be performed under the condition of not only steady state but also transient state. Hence, the proposed sensorless control scheme is basically robust against rotor resistance variations. Especially, the rotor resistance estimation is performed simply without calculating troublesome trigonometric functions and complicated integral computation. Moreover, the sensorless control scheme has no current minor loop to determine voltage references. It contributes to good control performance at low speed area. Some simulation results supported by experiments are given to show the effectiveness of this method