Favourable slot and pole number combinations for fault-tolerant PM machines

A new approach is described for selecting pole and slot numbers for fault-tolerant permanent-magnet machines so that there is inherently negligible coupling between phases (regardless of other design detail). The preferred slot and pole number combinations thereby help to ensure that a fault in one phase does not undesirably affect the remaining unfaulted phases. Other well-known criteria for fault-tolerant operation, including high phase inductance, also have to be met. It is demonstrated how particular slot and pole combinations can be used to eliminate low pole number armature MMF, thereby reducing the vibration and stray loss present during normal operation.