Lumped parameter thermal network for thermal analysis of a rotor-excited axial flux switching machine with electromagnetic-thermal design

Abstract

In this paper, a three-dimensional (3-D) lumped parameter thermal network (LPTN) model is presented for the first time for a rotor-excited axial-field flux-switching permanent magnet (RE-AFFSPM) machine. The 3-D LPTN predicts the steady-state temperature of different parts in various operating conditions. To enhance the LPTN accuracy and comprehensiveness, (i) the convection heat transfer in the internal and external areas, as well as radiation from the end-windings, (ii) core material anisotropic thermal conductivity, (iii) the equal thermal conductivity of the winding in the slot, and (iv) contact thermal resistances are all considered. Heat transfer coefficients are obtained mathematically to be applicable for the RE-AFFSPM machines with different parameters. A 3-D finite element method (FEM) is established to calculate the electromagnetic losses and thermal analysis with high accuracy. Eddy current losses in the stator core, rotor core, permanent magnets (PMs), and carriers, along with hysteresis losses in the stator and rotor cores, are calculated by 3-D FEM then coupled to the thermal analysis to predict the temperature distribution. By comparing the temperature results of the 3-D LPTN and 3-D FEM at various speeds, air–gap lengths, loading levels, and simultaneous variation of the current density and speed, the performance of the proposed 3-D LPTN is further investigated and verified. Results indicate that by the proposed 3-D LPTN, components temperature can be approximated with high accuracy in a lesser time than the 3-D FEM.