Asymmetrical Geometries in Electrical Machines

This paper describes and classifies possibilities of using asymmetric geometry solutions in slotted electrical machines with nonlinear soft magnetic core. These asymmetrical optimizations can reduce cogging torque and torque ripple at the nominal load. Additionally, some of them can improve overload capability, and field weakening capability by proper optimization of over-saturated regions of soft magnetic core. In this paper it is shown that the geometry of the soft magnetic core regions of TC-PMSMs, exhibiting strong saturation due to the interaction of PM- and armature reaction fluxes, has a significant impact on the torque quality. Therefore, by their modifications (including asymmetrical) it is possible to improve the machine characteristics. Two types of PMSM rotor arrangements (embedded-magnet rotor PMSM and rotor-surface magnet PMSM) were simulated with 2D FEM. The results showed that slight modification of the TC-PMSMs soft magnetic regions near by the air gap which exhibit the strongest saturation can lead to significant torque quality variation as well as to synchronous inductance changes.