Comparative study of the electromagnetic performance of switched flux permanent magnet machines

Switched flux permanent magnet (SFPM) machines have significant potential for many industrial applications because of their doubly salient structure, similar to switched reluctance machines. In recent years, several novel SFPM machine topologies, such as multi-tooth, E-core and C-core, have been developed to reduce the usage of permanent magnet materials without sacrificing the torque capability. A comparative study of the electromagnetic performance of these topologies, together with conventional SFPM machines having different stator/rotor pole combinations, that is, 12/10, 12/13 and 12/14, is presented. In addition to open circuit and electromagnetic torque performance, their torque-speed characteristics are investigated and compared. It is found that for conventional SFPM machines, the higher the rotor pole number, the better the flux-weakening capability, and higher maximum speed can be achieved. In contrast, owing to high d-axis inductance in the multi-tooth, E-core and C-core machines, infinite maximum speed can be obtained. Moreover, among all these machines, the multi-tooth machine has the highest flux-weakening factor, while the E-core machine exhibits the largest power capability. In addition to two-dimensional (2D) finite-element analysis (FEA), 3D-FEA is also performed accounting for the end effect. Finally, the torque-speed characteristics of prototype SFPM machines are measured to verify the FEA.