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. Finite-element analysis (FEA) simulations are presented to support the analytical calculations. The analysis indicates 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 subharmonics due to the magnet field but can reduce the subharmonics 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.