I. Introduction
Detuned operation of vector-controlled induction machines may result from the variation of motor parameters that are present in the control scheme but are regarded as constant, and from phenomena that are not modeled at all in the controller development and are therefore unaccounted for. The first group includes thermal variation of stator and rotor resistance, frequency related variation of rotor parameters, and variation of magnetizing inductance and stator and rotor leakage inductance due to saturation. The existence of phenomena that are normally entirely ignored in the modeling is more difficult to deal with, since these typically require an appropriate expansion of the basic electromagnetic induction machine model, from the fourth to a higher order. One such phenomenon is the iron loss. Its inclusion results in the sixth-order machine model [1], and core losses lead to a certain amount of detuning in vector-controlled induction machines, since standard vector controllers are unaware of the iron-loss existence [1]. Typically, an equivalent iron-loss resistance is used to model the iron loss and it is placed either in parallel to the magnetizing branch or immediately after the stator resistance in the dynamic equivalent circuit [1]–[4].