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.

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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 and 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 In the current and flux observers all of the terms that contain the rotor time constant and the rotor speed have been replaced by the sliding mode functions, thus making the proposed current and flux estimations completely insensitive to the rotor time constant variation and any error in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.

Abstract-Interior permanent magnet (IPM) synchronous machines are vulnerable to uncontrolled generator (UCG) faults at high speed that can damage the inverter. One approach to reducing this risk is to impose limits on the maximum machine back-emf voltage at top speed. This paper presents the results of a comparative design study that clarifies the nature and extent of the penalties imposed on the IPM machine metrics and performance characteristics as a result of imposing progressively tighter values of back-emf voltage limits. As an alternative to limiting back-emf and penalizing machine designs, this paper also investigates the effectiveness of the system-side protection approach to the same UCG fault problem.