Comparative Study of Novel Variable Flux Reluctance Machines With Doubly Fed Doubly Salient Machines

This paper presents a comparative study between novel variable flux reluctance machines (VFRMs) and doubly-fed doubly salient machines (DFDSMs), having the same stator outer diameter and axial length. For comparison, a 6-pole stator is used in VFRMs and DFDSMs, while a 5-pole rotor is optimized for VFRMs and a 4-pole rotor for DFDSMs. Compared with DFDSMs in which the flux-linkage and back-EMF are asymmetric particularly under heavy magnetic saturation, they become symmetrical and essentially sinusoidal in the VFRMs. Hence, the torque ripple in VFRMs can be significantly reduced. Further, due to the shorter flux path in the VFRMs, their average torque under the same copper loss can also be increased by 20% similar to 30% for the optimally designed VFRMs and DFDSMs within the same space envelop.