Effects of armature windings embedding methods on magnetomotive force of rare earth permanent magnet brushless DC motor

To our knowledge, in most cases, two sets of armature windings are embedded in every two stator slots of a dual-windings rare earth permanent magnet (REPM) brushless DC motor (BLDCM). The motor thus made is costly and complicated in its structure. To overcome these shortcomings, we used a new method for embedding two sets of armature windings in the same stator slot. We compared the magnetomotive force (MMF) of the dual-windings REPM BLDCM when it used the every two stator slots embedding method with that of this motor when it used the same stator slot embedding method in the single-windings scheme and in the dual-windings scheme respectively. The comparison results show that: when the dual-windings REPM BLDCM is working in the single-windings scheme and uses the same stator slot embedding method, the flux weakening effect of the armature MMF is less than that which uses the every two stator slots embedding method; when the dual-windings REPM BLDCM is working in the dual-windings scheme and uses the every two stator slots embedding method, the flux weakening effect of the armature MMF is less than that which uses the same stator slot embedding method. Therefore it is concluded that the every two stator slots embedding method should be used under the normal condition when the dual-windings REPM BLDCM is working in the dual-windings scheme; the same stator slot embedding method should be used under the normal condition when the dual-windings REPM BLDCM is working in the single-windings scheme. Finally we carried out the finite element simulation of the air gap magnetic flux density distributions of armature MMF, no-load magnetic field and load magnetic field and the speed-torque. The simulation results and the results of their comparison with the tested speed-torque curves of the prototype motor that uses the every two stator slots embedding method agree well with the theoretical analysis results.