Sensorless control of induction motors with simultaneous on-line estimation of rotor resistance and speed based on the feedforward torque control scheme

In this paper, a new speed sensorless induction motor scheme which can work at any speed including the zero speed is presented. The proposed method is robust to rotor resistance variations. Simultaneous on-line estimations of speed and rotor resistance are realized based on a feedforward type torque control scheme. The rotor flux with a low frequency sinusoidal waveform is used to help the estimation. The control scheme has no current minor loop to determine voltage references. Since the proposed estimation does not depend on any derivative terms of currents and stator voltages it contributes to speed sensorless with good performance at very low speed region. Furthermore, the proposed control is simply using motor parameters and stator currents without determining any PI gains for current feedback and any signal injection for the rotor resistance estimation. Simulations results supported by experiments are given to show the effectiveness of this method.