Sensorless second-order sliding-mode speed control of a voltage-fed induction-motor drive using nonlinear state feedback

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.