Analytical estimation of torque enhancement of the SR machine with saw-shaped (shark) pole surfaces

The paper presents an electromagnetic analysis of the switched-reluctance (SR) machine with saw-shaped (shark) pole surfaces. This design aspect facilitates an increase of the 'maximum/minimum' inductance ratio, relative to the flat-pole structure, and, as such, it has drawn attention as a concept for the enhancement of the 'torque/volume' ratio. The analysis is based on the analytical model for estimation of the minimum and maximum inductances, which determine the extreme flux-linkage against current characteristics. These characteristics are used to predict the average phase torque at a constant current, from a given set of geometric parameters and the B-H curve describing the machine. The optimisation of the axial airgap profile is carried out by varying the tooth angle and the axial airgap pitch of the shark structure, while the other geometric parameters were kept the same as in the conventional (flat-pole) machine, which was optimised to produce the maximum torque/volume ratio. The maximum torque achievable with the shark machine is compared with the torque of the conventional SR machine at their rated currents.