Detuned operation of vector controlled induction machines due to stray load losses

Stray load loss, as a possible source of detuned operation of vector controlled induction machines, has never been considered before. The purpose of this paper is to investigate the impact of stray load losses on accuracy of indirect rotor flux oriented (RFO) control of a current-fed induction machine by developing an analytical model. Detuning is characterized by means of the orientation angle error, actual to reference rotor flux ratio, and actual to reference torque ratio. In order to be able to evaluate the stray load loss induced detuning quantitatively, stray load losses are at first experimentally determined for two induction machines of different ratings, using the procedure outlined in IEEE 112-B standard. The parameters of a motor equivalent circuit that accounts for the stray load losses are further fitted to the measurement data and the impact of stray load losses on accuracy of field orientation is assessed. It is shown that stray load losses affect vector control to a much smaller degree than the iron losses, even when the two are of approximately the same and rather high value in the rated operating point.