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This paper presents a speed-estimation method for the induction-motor (IM) drive that is based on a special current-control scheme called integral sliding-mode current control (ISM-CC). classic current control for the IM drive is done by regulating the d-q synchronous reference frame currents using PI controllers with or without a decoupling compensator. If a decoupling compensator is used, the speed and the motor parameters are needed to compute the decoupling voltages. Often, the speed (or the speed estimate) is not available, and the decoupling compensator is omitted; this leads to a degraded performance of the current controller. The ISM-CC scheme was developed for the decoupled control of the d-q currents and does not require the knowledge of the speed. In the ISM-CC, PI controllers act on simulated ideal plant models, and the resulting command voltages are complemented with voltages generated by SM controllers. It is shown that the SM controllers play the same role as the compensation voltages produced by a decoupling compensator. The speed estimator is constructed based on this observation-speed is estimated through algebraic calculations. This paper describes both the ISM-CC method and the speed estimator. Simulations and experimental results on a 1/4-hp three-phase IM confirm the validity of the method.
Date of Publication: Sept. 2009