Edinburgh Napier University

  A high-performance and robust sensorless speed-control scheme of a voltage-fed
induction motor has been developed in which the control of speed and flux is decoupled. A robust
control strategy, specifically a sliding-mode technique, is considered here. Standard sliding-mode
control is a type of nonlinear controller and is robust to system uncertainties and parameter
variation. However, it suffers from the chattering problem. Higher-order sliding mode (HOSM) is
one of the solutions which does not compromise robustness. In particular, a super-twisting higherorder
sliding-mode algorithm coupled with equivalent control is considered in the paper for both
speed and flux control of the motor. A design procedure is developed to determine the controller
gains. Although the use of HOSM control provides robustness, accurate knowledge of rotor flux
and machine parameters is still the key factor in obtaining a high-performance and high-efficiency
induction-motor drive. Sensorless flux-estimation schemes discussed in the literature suffer from
problems associated with pure integration, instability and sensitivity to stator-resistance mismatch
at low-speed operation. In the paper, a stable sensorless adaptive rotor-flux estimator using the full
induction-machine model is proposed. Stable-model-reference-adaptive-system (MRAS) speedand
stator-resistance estimators based on current estimation are proposed and design details are
presented. A stable load-torque MRAS estimator has also been developed. Experimental results are
presented to verify the stability of the induction-motor drive in various operating modes.