Influence of end-effect on torque-speed characteristics of various switched flux permanent magnet machine topologies

Switched flux permanent magnet (SFPM) machines have the permanent magnets (PMs) and armature windings on the stator, and therefore, simple and robust rotor and easy management of the temperature can be achieved. However, the spoke location of the PMs causes not only flux leakages outside the stator but also large flux leakage in the end region, i.e. end-effect, which could result in a large reduction in the electromagnetic performance. Therefore, the influence of the end-effect on the torque-speed characteristics of three conventional SFPM machines having different stator/rotor pole combinations, i.e. 12/10, 12/13 and 12/14 as well as three novel topologies with less PMs, i.e. multi-tooth, E-core and C-core are investigated and compared in this paper. In order to obtain the end-effect influence, 3D-finite element analyses (FEA) results are compared with their 2D-FEA counterparts and validated by experiments. It has been concluded that due to end flux leakage, lower torque capability in the constant torque region is observed in the six machines. However, at high current levels, improved flux weakening capability in the conventional machines can be exhibited, while the large inductance causes lower power capability in the multi-tooth, E-core and C-core machines.