Comparative study of wound-field flux-switching machines and switched reluctance machines

Abstract

In this paper, comparisons between two permanent-magnet-free (PM-free) machines, namely a wound-field flux-switching machine (WFFSM) and a switched reluctance machine (SRM), covering skewed-rotor and straight-rotor structures are conducted. The topologies and operation principles of the WFFSM are illustrated firstly. Then, the effects of rotor skewing angle on static characteristics, e.g., open-circuit phase flux-linkage and back electro-motive-force due to field currents, electromagnetic torque, and torque ripple, have been investigated in depth by finite element analysis (FEA). Consequently, the optimal rotor skewing angle is determined. In addition, comparisons between the WFFSM and a prototype SRM having the same stator outer diameter and stack length are conducted, and the results indicate that for both PM-free machines, the skewed-rotor WFFSM exhibits better performance, including larger torque capacity and smaller torque ripple. Moreover, the reductions of average torque and torque ripple due to rotor skewing for the WFFSM are acceptable, whereas for the SRM rotor skewing results in degraded performance.