After conditions for observability of a linearized induction machine model are examined, an approach for speed-sensorless flux estimation based on two-time-scale theory is developed. This approach relies on the natural time-scale separation between the electrical and mechanical dynamics of the induction machine. A full-order observer of an induction machine is presented, incorporating a correction term which has an intuitive explanation when one considers steady-state stator currents. Using two-time-scale theory, convergence of the observer is shown for all stable operating points of the induction machine with the exception of DC excitation. Sensitivity of the observer to parameter deviations is discussed. Experimental results are presented confirming the validity of the above approach.
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