Comparative Analysis of Variable Flux Reluctance Machines With Double- and Single-Layer Concentrated Armature Windings

In this paper, the variable flux reluctance machines (VFRMs) with double- and single-layer concentrated armature windings are comparatively analyzed. First, the single-layer winding is found to have an identical winding factor as a double-layer winding, but significantly larger peak value of magneto-motive force, which will result in severe local saturation in cores of VFRMs with single-layer winding. Then, based on the magnetic gearing effect and finite-element analysis, the electromagnetic performances of VFRMs with both winding types are compared. The VFRMs with single-layer winding are proved to be always lower in average torque, higher in torque ripple, larger in iron loss, and lower in efficiency than those with double-layer winding. Nevertheless, better fault-tolerance capability is achieved for a single-layer winding due to its physical separation between phases and larger phase self-inductance. Overall, the double-layer armature winding is the preferable choice for the VFRMs. Finally, a 6-stator-slot/4-rotor-pole VFRM with both double- and single-layer windings is prototyped for verification.