Introduction
Detuned operation of vector controlled induction machine drives occurs due to variations of motor parameters that are treated in the control algorithm as constant values, and due to the phenomena that are not modelled at all and are therefore unaccounted for in the controller design [1]. While all the detuning sources of the first group, as well as the iron losses (that belong to the second group), have been studied in detail in the past, stray load loss as a potential source of detuning has attracted more attention only recently. Stray losses appear in any ac machine. Higher flux density harmonics due to slotting effects, inter-bar rotor currents and skewing are responsible for their existence [2]. One part of the stray losses will exist under all operating conditions, including no-load condition (stray no-load losses), while the other part of the stray losses will appear when the machine is loaded and will in general vary with the loading and operating frequency (stray load losses) [3]. Stray no-load losses are in equivalent circuit representation lumped together with the iron losses and therefore the relevant part that remains unmodelled is the stray load loss.