Systematic Analysis of the Design Principle of Fractional-Slot Sinusoidal Windings

Abstract

Fractional-slot winding machines have been widely used in electric vehicles, aerospace, and other fields due to advantages such as high power density. However, the high magnetomotive force (MMF) harmonic content has, to some extent, limited their further development. To this end, this article systematically analyzes the design principle of fractional-slot sinusoidal windings (FSSW) under different pole-slot combinations, so that only the fundamental and slot harmonics remain in the MMF. First, a conductor arrangement method for FSSW is proposed: based on the coil axis (CA) and the positions of positive and negative slot numbers in the fundamental slot number phase diagram, the conductors of each phase form a double-layer concentric configuration for both odd and even denominators of the number of slots per pole per phase. Then, by utilizing the periodicity of winding factors, the turns ratios among coils that eliminate all other MMF harmonics are analyzed for any number of coils. Next, FSSW designs under different pole-slot combinations are verified by finite element analysis (FEA) to examine the MMF harmonic content. Finally, a permanent magnet synchronous motor (PMSM) with an FSSW and a slot per pole per phase of 3/2 is manufactured to further verify the analysis.