An Assessment of Wound-Rotor Synchronous Machines with Hairpin Windings for Automotive Traction Drives

This thesis investigates the wound-rotor synchronous machine as traction machine for electric vehicles and the usage of hairpin conductors to build up its armature’s windings. Although the wound-rotor synchronous machine has been researched, designed and manufactured for decades, its adoption in variable speed drives targeting automobiles is still limited. Employing a wound-rotor synchronous machine, the field current, and thus, the rotor flux can be tuned to improve performance criteria for every operating point. The second key topic covered is the usage of hairpin windings in the machine’s armature. Using this approach, prefabricated hairpins are shaped by means of bending processes, inserted into the armature’s slots and connected to each other to realize the phase windings. As these processes are well suitable for mass-production, hairpin windings are promising means to avoid bottlenecks during manufacturing. Yet, the evaluation of the impact of eddy current effects in the armature conductors is not trivial. Due to the variability of the operating points of automotive traction machines, classical design rules aiming for an optimal conductor size are not applicable. This thesis employs analytical and numerical methods to quantify the additional ohmic losses introduced by eddy-currents. Furthermore, the manufacturing process of hairpin windings and considerations when choosing the winding layout are clarified. To analyze both key topics simultaneously and investigate the interplay between the variability of operating points and the impact of eddy-currents, a machine model is proposed that can capture effects such as eddy-currents and core saturation while still being computationally fast.