Design and tests on a fractional-slot induction machine

This paper considers the design of fractional-slot induction machine. An analytical model is used to identify the best combinations of stator slots, rotor slots and pole pairs. Multi-layer windings (with more than two layers) are considered in both the stator and the rotor to reduce the MMF space-harmonics amplitudes and so to limit the torque ripple. After the general design procedure for the multi-layer windings, an application example is presented. Thanks to the adoption of multi-layer windings, a considerable reduction of the torque ripple is achieved. Both predictions and experimental tests on two prototypes are included in the paper.