Investigation of winding MMF harmonic reduction methods in IPM machines equipped with FSCWs

In this paper, implementation of fractional-slot concentrated windings (FSCWs) into an interior permanent magnet (IPM) machine, designed by using the same geometrical and operational specifications as Toyota Prius 2010 IPM machine, has been presented. In detail, the Toyota Prius's IPM equipped with integer-slot distributed windings has been considered as a reference machine. Then the geometry of the stator has been adequately modified in other five models to equip FSCWs and adopt different magnetomotive force (MMF) reduction methods. It has been validated that the FSCW technique causes a significant increase in the rotor losses due to increase in the rate of the total harmonic distortion of the MMF harmonics. To reduce the effect of these harmonics, different MMF harmonic reduction methods including phase-winding coils with different number of turns, multilayer winding with phase shifting, and stator with flux barriers have been investigated. To reveal the effectiveness of the investigated MMF harmonic reduction methods, the key thermal and electromagnetic performance characteristics including torque, torque ripple, power losses, and efficiency have been numerically calculated by finite element method and have eventually been compared.