Potentials and Limits of Three-Phase Fractional-Slot Concentrated Winding Optimization

Fractional-slot concentrated windings (FSCWs) in three-phase permanent magnet machines are popular for several advantages but may cause severe performance issues due to their richness in air-gap magneto-motive force (MMF) space harmonics. This paper intends to explore the potentials and limits of FSCW optimization through multi-layer arrangements when applied to mitigate three problems, namely: permanent-magnet eddy-current losses, unbalanced magnetic pull (UMP) and torque ripple. It shows that, regardless of the algorithm adopted, the winding optimization is effective only on well-defined slot-pole combinations, which are strongly different depending what the optimization target is. Permanent magnet loss minimization is shown to be the field where the most effective results can be achieved, while UMP and torque ripple can be mitigated by winding optimization to a smaller extent and for a limited set of slot-pole combinations.