Use of the star of slots in designing fractional-slot single-layer synchronous motors

Nowadays fractional-slot windings are proposed for synchronous motors for different purposes: reduction of end-winding losses, reduction of torque ripple, reduction of mutual coupling among the phases, fault-tolerant applications, and so on. The design of the single-layer fractionalslot synchronous motors is dealt with, in which each slot contains only one side coil. The star of slots, introduced some time ago, proves itself to be again appropriate. After a brief review of the classical theory of the star of slots, its application is extended to the design of these unconventional windings. Thanks to its graphical representation, a simple analytical formulation is carried out describing the harmonic contents of the winding distribution. Finally, the star of slots allows simple rules for the design of fractional-slot single-layer windings to be determined. As a special case, it is used to determine the synchronous motor winding solutions suitable for critical fault-tolerant applications.