On Air-Gap Approximations for Slotted Electrical Machine Models Assuming Radial Magnetic Fields

For modeling electrical machine characteristics with a high level of detail, one of the important aspects is to represent slotting effects on the air-gap magnetic field. In analytical model approaches, the stator and rotor slots typically influence the magnetic field indirectly as part of air-gap permeance. This work provides a comparison of state-of-art methods to approximate the air-gap permeance including slotting effects. The selected methods are compared with regard to spatial distributions of radial air-gap magnetic flux density and of exemplary flux linkages for a theoretical movable coil. As calculation basis, a cage induction machine at a static operating point is considered. The resulting magnetic flux density distributions illustrate the accuracy differences between the air-gap approximation approaches. Special focus lies on variations in the curve shapes, which are connected to rather generalizable method characteristics. Regarding the exemplary flux linkages, a majority of the approaches lead to strongly resembling results. In this context, computing efficiencies of the methods constitute a discussion point.