Theory and design of fractional-slot multilayer windings

This paper deals with fractional-slot multilayer windings. They are becoming attractive since they allow to reduce the harmonic content of the windings magneto motive force. Some examples of such a type of windings are reported in literature, but they are limited to a few slot/pole combinations. On the contrary, in this paper the general theory is presented. General rules for the design of multilayer windings are illustrated. It is also investigated when the adoption of a multilayer winding makes possible to limit the torque ripple and the rotor losses of the machine. Several examples and experimental tests are reported to investigate the advantages and convenience of adopting multilayer windings.