Quantification of End Turn Leakage Effects for a Double Stator Single Rotor Axial Flux Machine

Paper in proceeding, 2025

Accurate consideration of end leakage inductance is essential to avoid overestimation of the high-speed output power in permanent magnet synchronous traction motors. However, the end leakage inductance is often neglected or estimated empirically, since its calculation involves a time-consuming Three Dimensional (3D) Finite Element Method (FEM), together with the normally used Two Dimensional (2D) FEM model. Most of the end-turn leakage inductance calculations in the literature are for Radial Flux Machines (RFMs). This paper investigates the possibilities of using a modified 2D FEM model that can incorporate the estimated end leakage effects of an off-the-shelf 4kW Axial Flux Permanent Magnet (AFPM) machine with Concentrated Windings (CWs). Such calculation methods can be used efficiently for optimization and control purposes. Two methods from literature are examined and adapted whereof, one method is originally proposed for RFMs and the other method was suggested for single-layer AFMs. It is found with FEM that the end-turn leakage inductances in the d- and q-directions are 22% and 21% of the total d- and q-axis inductance, respectively. The impact on the maximum high-speed power shows around 10% decrease. The investigated analytical/empirical methods found from the literature fail to capture the end-turn inductance well, with the best guess of a 30% lower value compared to FEM simulations.