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This paper presents a continuous approach of sliding-mode current and flux observers for an induction machine. The proposed observer structure both decouples machine equations and makes them completely insensitive to rotor resistance variation. An estimation algorithm based on these observers is proposed to calculate speed and rotor resistance independently. In the proposed algorithm, the speed and rotor resistance are considered to be unknown constants, because the speed and rotor resistance change slowly compared to the electrical variables such as currents and fluxes. The simulation and experimental results demonstrate the good performance of the proposed observer and estimation algorithm and of the overall indirect-field-oriented-controlled system. Index Terms--Current and flux observer, induction machine (IM), speed and rotor resistance estimation.

A new close loop current model flux observer is designed to estimate the rotor flux, position and velocity of an induction machine. The current observer includes carefully designed sliding mode functions which are derivative of the fluxes along the [alpha] and [beta] axes. Therefore, when the estimated current converges to the measured one, the flux estimation is a mere integration of the sliding mode function. The rotor speed can then be derived from the sliding mode functions and the estimated flux. In the current and flux observers all of the terms that contain the rotor time constant and the rotor speed have been replaced by the sliding mode functions, thus making the proposed current and flux estimations completely insensitive to the rotor time constant variation and any error in the estimated speed. Simulations and experiments are performed under a variety of conditions to validate the effectiveness of the proposed algorithm. Index Terms--Current model flux observer, induction machine, sensorless control, sliding mode.

In this letter, a new sliding-mode sensorless control algorithm is proposed for the field-oriented induction machine drive. In the proposed algorithm, the terms containing flux, speed, and rotor time constant, which are common in both current and flux equations, in the current model of the induction machine are estimated by a sliding function. The flux and speed estimation accuracy is guaranteed when the error between the actual current and observed current converges to zero. Hence, the fourth-order system is reduced to two second-order systems, and the speed estimation becomes very simple and robust to the parameter uncertainties. The new approach is verified by simulation and experimental results. Index Terms--Induction motor, field-oriented control, sensorless control, sliding mode.