An Investigation of Substituting Copper with Aluminum Conductors in a High Power, Medium Speed SPM Machine

High performance permanent magnet machines are capable of achieving high torque densities and high efficiency. Producing a stator winding with a high slot-fill is a key factor in realizing a high torque density. Solid bar conductors which are a good match with the slot dimensions offer a route to high slot fill but these can suffer from prohibitive levels of associated AC loss. Litz wire and/or aluminum conductors offer a route to managing AC conductor loss, albeit at the expense of increased quasi-static ohmic loss. To fully utilize the benefits of alternative conductor configurations or materials, careful design and optimization processes are required. In this paper, the optimal material resistivity for baseline model is first evaluated over a range of excitation frequencies. Finite-element based simulation results indicate that for the particular machine design, and at certain frequency, direct substitution of copper bar with aluminum bar will be beneficial. Based on these findings, two alternative substitution strategies are proposed: partial and asymmetrical substitution This process is achieved by implementing two separate three phase windings. By adopting partial or asymmetrical aluminum designs, aluminum conductor can even outperform copper in lower frequency ranges in terms of total loss and weight.