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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 fractional-slot 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.
Date of Publication: 1 May 2006