Considerations on selecting fractional-slot windings

The paper focuses on the optimal selection of a fractional-slot winding for PM machines. The choice of the proper combination of slots and poles, and the corresponding winding layout, has a major impact on the PM machine performance, such as torque ripple, torque density, harmonic contents and then induced rotor losses, as well as capability to limit the short-circuit current and other fault-tolerance features. Among the very large possibilities to choose a winding configuration, the paper gives useful indications for a proper selection considering several aspects. The winding choice criteria are given using analytical equations, so that their implementation results to be easy. In this way, the collection of such criteria becomes an helpful tool in the design process.