Comparative study of alternative modular switched flux permanent magnet machines

The electromagnetic performance of alternative single layer modular switched flux permanent magnet (SFPM) machines, i.e. conventional, C-core, E-core and modular, is compared by finite element analysis in this paper. The comparison includes winding factor, open-circuit flux density, back-EMF and electromagnetic torque, together with the influence of four slot/pole number combinations (12s/10p, 12s/11p, 12s/13p and 12s/14p). It is found that with flux gap the electromagnetic performance of modular SFPMMs does not necessarily degrade. The flux focusing and defocusing effects are observed in the C-core and some of the E-core machines. However, the flux defocusing effect occurs in all modular machines with large flux gap openings. Since the flux gap opening affects the slot area, the copper loss will be changed as well. Hence, the variation of copper loss against flux gap opening for the same current or the same torque has also been investigated.