Magnetic Structure Based Improvement of Output Torque of Switched Reluctance Machine: A Review

This paper reviews research reported over the last three decades on enhancing the torque density of a switched reluctance machine (SRM) through improved magnetic structure of the machine. To this effect, various pole configurations, modifications to pole geometry such as introduction of teeth in stator poles, tapering of stator and rotor poles, non-uniform airgap, introduction of flux barriers in the poles, and segmental rotor are studied. All salient points in the review are supported by comparative analyses based on finite element analysis (FEA) of candidate machine designs. Increasing the number of rotor poles and introduction of teeth in stator poles enhance the torque density at low current density, while increasing multiplicity is beneficial at high current densities. Quantum of electromechanical energy conversion per individual stroke can be increased by tapering of poles, non-uniform airgap and by introduction of flux barrier in the poles. A segmental rotor can increase the stator winding flux-linkage for a given excitation, and thereby, the torque output of the machine.