Lumped parameter thermal network model investigations for an electric machine stator with flux barriers

To achieve electrification of small aircraft propulsion systems, high power density electric motors are required. The latter entail thermal losses that need to be dissipated for the machine to operate properly. Electric machines with flux barriers at stator can provide reduced harmonic losses and higher power densities. In addition, barriers provide a shorter thermal path for heat generated in the center of the machine compared to more traditional configurations. This paper presents the setup and validation of a lumped parameter thermal network (LPTN) model of a flux barrier permanent magnet motor developed in Simulink and comparing it to a computational fluid dynamics (CFD) conjugate heat transfer (CHT) simulation conducted in ANSYS Fluent. The validation is performed only on the stator because it is the component that presents a change in the possible heat paths. The LPTN model is a detailed model that includes lamination, slot windings, end windings and contact resistances. The effect of the LPTN additional discretization in axial, tangential and radial directions is tested with respect to the estimation of surface, inner and hot spot temperatures. The refinement in the axial direction proved to be the most significant for the estimation of temperatures in the case of an air-cooled machine. Alternative spatial discretization is tested and shows an improvement of the estimation of the surface temperature of certain regions.