Winding factors and magnetic fields in permanent magnet brushless machines with concentrated windings and modular stator cores

Removing some sections of the stator yoke in a permanent magnet brushless machine can be beneficial for reducing punching waste and simplifying motor manufacture. However in some cases, restricting the possible flux paths in this way will have a detrimental impact on the torque and air-gap harmonics. This paper discusses the potential implications of modular stator core arrangements and presents the air-gap flux density harmonics and winding factors for potential slot/pole combinations. FEA simulations are presented to support the analytical calculations. The analysis suggests that the performance reduction from using a modular stator is minimal when the number of slots and poles are similar but drops off substantially when this is not the case. A modular core stator will increase the MMF sub-harmonics due to the magnet field but can reduce the sub-harmonics due to the armature if a single layer winding is used. The effect of slotting is very similar for a modular and conventional core machine and FEA results match previously published analytical analyses.