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An adaptive controller for correcting the rotor time constant estimate used in the slip frequency calculator of indirect field oriented controllers is presented. The controller possess near digital deadbeat performance, and simultaneously maintains its correctness down to zero speed. The robust controller dynamics are based on an operating point form of digital deadbeat control. In this controller, an operating point approximate inverse model relates changes in the machine parameters to deviation in the rotor flux components. This allows nearly exact, one step (deadbeat) prediction of the correction necessary for the slip calculator gain.>
Moreira et al. (Mon,) studied this question.