A comparative study between aluminium and copper windings for a modular-wound IPM electric machine

This paper conducts a comparative study upon the performance of an electrical machine fitted with alternative winding conductor materials. The study focusses on an existing interior-mount PM machine (IPM), which is wound with copper (Cm) conductors in a single-layer “modular” topology. An analysis exercise is performed to investigate the impact of using alternative conductor materials, such as Aluminium (At). The studied machine employs profiled rectangular conductors, which can offer many performance and manufacturing benefits. It is however acknowledged that windings formed from large section conductors frequently suffer from elevated ac losses, e.g. from high-speed and/or high frequency operation. In this context, replacing commonly used Cm windings with a material of higher electrical resistivity, such as Al, is an interesting alternative. The immediate impact would be an increase of dc winding resistance and therefore elevated dc losses. However, under high-frequency operation, the increased material resistance helps to abate the effects of ac loss. A more detailed approach for the loss and efficiency derivation is provided herein, accounting for magnetic saturation and stator current vector in field weakening operation. Theoretical predictions suggest that the use of Al conductors offer benefits to performance under certain operating conditions and are a viable alternative to the commonly used Cm counterpart. In the analysed case, only a moderate reduction in machine performance is experienced at lower speed ranges. The mathematical models used in this work were informed from tests on a hardware prototype to provide more reliable machine performance predictions.