Eddy Currents in the End-Windings of High Power Density Traction Machines

The main requirement for electrical machines used for traction motor applications are torque density and efficiency. Conductors with large cross section area, such as form wound-or hairpin-winding, are a popular option to increase both. However, they suffer from increased eddy current loss when being exposed to time varying magnetic fields. In this paper, such additional eddy currents in the end-windings of hairpin winding traction machines are investigated and assessed. It is shown, that commonly used analytical approaches underestimate the losses significantly at high speed and hence are not suitable for an accurate evaluation. As alternative, an FEA based workflow is applied to evaluate the influence of additional eddy currents within the full drive map of an example 150kW study case traction machine. The results show an significant increase of eddy currents, especially for high speed operation points at high load and underline the importance of accurate evaluation.