Detuned operation of rotor flux oriented induction machines in the field-weakening region due to iron loss

Iron loss, traditionally ignored in vector control schemes, inevitably causes certain detuning during operation of a rotor flux oriented induction machine. The studies that discuss detuning in the base speed region, for operation at rated speed with rated rotor flux command, are already available. However, it appears that no detuning study has been performed for the field-weakening region so far. Any such study would require identification of equivalent iron loss resistance at frequencies other than rated. The aim of this paper is twofold. Firstly, an experimental method that enables identification of equivalent iron loss resistance over the frequency range of interest is described and experimental results are presented. Then, the equivalent iron loss resistance values are utilised in evaluation of detuning in the field-weakening region, for speeds up to five times rated. Detuning in the field-weakening region is found to be significantly in excess of the one met at rated speed, if the machine operates at high speeds with relatively light loads.