On the computation of rotor losses through a set of harmonic finite element analyses in fractional-slot concentrated-coil permanent-magnet machines

In fractional-slot concentrated-coil permanent-magnet machines, where the number of stator slots is close to the number of poles, large MMF space harmonics appear in the airgap due to the strongly non-sinusoidal winding distribution. Major effects of such harmonics are the eddy-current losses in rotor permanent magnets. For computing these losses, the use of harmonic finite-element (FE) analysis instead of a time-stepping FE approach is advantageous in terms of computational time and resources. Nevertheless, the possible interaction between different rotating harmonic fields is to be suitably considered. The paper shows how this can be done and gives a numeric application example referring to a 9-slot 8-pole machine.