Litzpins: Hybrid Solid-Transposed Hairpin Conductors Enabled By Additive Manufacturing

Hairpin windings are gaining increasing industrial and research attention as they are an attractive option for high power-density electrical machines, offering advantages in automated manufacture, batch consistency, and good thermal performance owing to high slot fill-factor and end-windings that lend well to spray cooling thermal management techniques. However, the large section conductors in proximity to the air-gap are prone to high levels of AC loss, particularly for high speed or frequency operation, or when inverter current waveform harmonics are pronounced, which limits performance. Methods proposed to address these high levels of non-uniform AC loss include increasing the number of conductor layers, using asymmetric conductor heights, radially segmenting individual hairpins, or combining rectangular litz with solid conductors to minimize AC loss by continuous transposition. However, these methods typically reduce overall winding packing factor and increase the complexity of the end-winding connections by requiring joining of dissimilar conductor types. In this paper, hybrid solid-transposed hairpin conductors termed Litzpins are introduced in which metal Additive Manufacturing is employed to create a seamless transition from solid to litz-type transposition, only in regions prone to AC loss, with a high degree of control over the number of parallel strands and pitch to optimally reduce AC loss. Prototype Litzpins are manufactured and experimentally assessed against conventional and asymmetric hairpin arrangements showing significant improvement in AC loss performance when used as drop-in replacement conductors.