Influence of end-effect and cross-coupling on torque-speed characteristics of switched flux permanent magnet machines

Switched flux permanent magnet (SFPM) machines have the synergy of PM machines, including high torque density and high efficiency, and switched reluctance (SR) machines, such as simple and robust rotor structure. Therefore, they are potentially attractive for many applications, ranging from traction to aerospace. Comparing with conventional SFPM machines, multi-tooth SFPM machines have additional advantages of using less magnet material but higher torque capability. This paper investigates the influence of the end-effect and cross-coupling on the torque/power-speed characteristics of a multi-tooth (6-4 stator pole/tooth, 19-rotor pole) SFPM machine. Various models at different cross-coupling levels are considered, viz. full cross-coupling on both PM flux linkage and dq-axis inductances, partial cross-coupling on the PM flux linkage only and without cross-coupling. It is found that the partial cross-coupling model, which is much easier and faster, exhibits almost the same accuracy as the full cross-coupling model. Furthermore, the end-effect causes a large reduction in torque-speed characteristics. However, such reduction is more significant in the flux weakening operation region, as confirmed by the 3D finite element (FE) and experimental results.