An improved rotor resistance estimator for induction motors adaptive control

An online rotor resistance estimator for induction motor adaptive control is presented. The rotor resistance scheme uses the rotor speed, the stator current, voltage provided by the controller, time-derivatives of the stator current and voltage. The time-derivatives of the stator current and voltage are estimated using 2nd order sliding mode observer. The finite time convergence of the estimated rotor resistance to the nominal value is achieved when the classical persistent excitation condition is satisfied by the input signal. The method is suitable for online operation to continuously update the rotor resistance value. Experimental results with online variation of the rotor resistance show that the proposed algorithm gives better performance compared to the previous work. The other interesting feature of the proposed method is the robustness properties with respect to the variation of the stator resistance both at relatively high speed and low speed.