Induction Machine Speed Estimation - Observations on Observers

University dissertation from IEA, LTH, Box 118, S-221 00 LUND, SWEDEN

Abstract: This work focuses on observers estimating flux linkage and speed for induction machines, mainly in the low speed region. With speed estimation, sensorless control is possible, meaning that the speed of induction machines without mechanical speed sensors can be controlled. The observer based sensorless drive system has superior dynamic performance compared to a system with an open loop frequency inverter, yet it is neither more complex nor expensive. Using mechanical equivalent models of the induction machine and observers, an accurate flux observer working in the entire speed region of the induction machine is presented. The flux observer is expanded into a combined flux and speed observer, measuring only stator current and voltage. A method for sensorless control is proposed, analyzed and experimentally verified. Observer and controller calculations are performed by a digital signal processor.

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