Soft Magnetic Composite Materials AC Properties and their Application in Electrical Machines

Abstract

Eddy current losses in alternating current electromagnetic applications are ruled by resistivity. The traditional solution is to use stacks of electro-steel sheets, which effectively break the induced current paths. However the lamination technique is normally applied in 2D-designs and in addition can become more costly and complex as the frequency of the application increases. Soft Magnetic Composites, SMC, are isotropic, have improved high frequency performance and can be compacted to 3D-shapes using the established powder metallurgy process. Excellent dimensional accuracy, smooth surfaces and flexibility in component design opens new dimensions for creating innovative 3D machine concepts. SMC-materials are basically pure iron powder particles coated with a very thin, electrically insulating layer. A range of Somaloy® products are available today and the range is being extended. An SMC material is defined, not only by the base powder, but also additive(s) selected and the processing route chosen. This allows tailoring of properties for specific application requirements. An overview of available SMC materials and properties achievable will be given. Thanks to SMC materials high resistivity and ability to carry flux in three dimensions complex flux paths in machine types such as transverse flux motors can effectively be produced on an industrial scale. Larger structures can be realized by dividing the core into segments. Joining is easily managed thanks to the possibility to integrate assembly features on SMC components. 3D flux path enables deeper and more efficient flux concentration. A low air gap flux density in e.g. a radial flux machine can be concentrated into the tooth body in the circumferential as well as the axial direction. This minimizes the winding turn length required. Flux can furthermore be distributed in the same directions in the core back realizing a radialy thinner core back, thus reducing the diameter of the machine. If the new design opportunities are carefully implemented, SMC-motors can successfully compete with lamination-motors even at grid frequencies. Recent progress in applications will be described as well as some examples of commercial products presented.