Permanent magnet brushless machines with minimum difference in slot number and pole number

This paper presents design, modeling and prototyping of three-phase permanent-magnet brushless machines having a fractional slot to pole ratio. In particular, permanent magnet brushless machines which exhibits slot number and pole number differ by either plusmn2 or plusmn1 will be considered. Such small difference in slot and pole numbers will potentially improve motor characteristics and subsequently result in better motor performance. Such fractional slot-pole number motors may also employ double-layer windings or single-layer windings in order to simplify the manufacturing process. Finite-element methods are first used to predict the flux-linkage, back-EMF and cogging torque waveforms, and they are shown to be in good agreement with the measured results. Two prototypes are built, the first motor has 12-slot/10-pole and the other motor has 9-slot/10-pole for test and validations.