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Identification of the Rotor Time Constant in Induction Machines without Speed Sensor



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1 Identification of the Rotor Time Constant in Induction Machines without Speed Sensor M Li J N Chiasson M Bodson L M Tolbert University of Tennessee ECE Department Knoxville USA The University of Utah ECE Department Salt Lake City USA The Abstract A differential algebraic method is used to estimate the rotor time constant TR of an induction motor without measurements of the rotor speed position The method consists of solving for the roots of a polynomial equation in TR whose coefficients depend only on the stator currents stator voltages and their derivatives Experimental results are presented Index Terms Rotor Time Constant Sensorless Speed Observer Induction Motor I I NTRODUCTION Induction motors are very attractive in many applications owing to their simple structure low cost and robust construction Field oriented control is now used to obtain high performance drive of the induction motor because it gives control characteristics similar to separately excited DC motors Implementation of a rotor flux field oriented controller requires knowledge of the rotor speed and the rotor time constant TR to estimate the rotor flux linkages There has been considerable work done in the last several years to implement a field oriented controller without the use of a speed sensor 1 2 3 4 5 6 However many of these methods still require the value of TR which can change with time due to ohmic heating that is to be able to update the value of TR to the controller as it changes is valuable The work presented here uses an algebraic approach to identify the rotor time constant TR without the motor speed information It is most closely related to the ideas described in 7 8 9 10 11 Specifically it is shown that TR satisfies a polynomial equation whose coefficients are functions of the stator currents the stator voltages and their derivatives A zero of this polynomial is the value of TR It is further shown TR is not identifiable by this technique under steady state conditions It is also



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