Hairpin Windings: An Opportunity for Next-Generation E-Motors in Transportation

Abstract

The advancements in electrical machines and power electronics technologies seem permitting to achieve the power density and efficiency levels required nowadays by the transportation sector. However, the reliability of components and of their production process is currently a challenge. This is especially true for electrical machines, whose winding processes are still far from obtaining the high levels of automation, programmability and repeatibility required by the transportation market. This article looks into hairpin windings and outlines a number of future [5]. Nevertheless, such new solutions often reflect on increased losses in cores and windings, with limited flexibility to suit the transportation production requirements. Hence, new winding concepts, and flexible and automatized manufacturing processes are required to mitigate these challenges, as EMs intended for transport applications require compact windings with high slot fill factor, low losses, high reliability, etc. This article further elaborates on the topics discussed in [5], first reviewing hairpin technologies with focus on the fill factor as a key enabler for power density, and then discussing their impact on AC losses,

Analysis of Voltage Distribution and Connections within a High-Frequency Hairpin Winding Model

“…Hairpin conductors are pre-formed wires which can achieve a high fill factor, thus also a higher slot thermal conductivity [10]- [15]. This aspect allows to increase the electric loading, especially at low frequencies, making them suitable for automotive applications requiring high torque densities.…”

AC losses reduction in Hairpin Windings produced via Additive Manufacturing

“…Currently windings represent one of the main bottlenecks, so unconventional solutions are required to improve the performance of electrical machines. Of these, hairpin windings are becoming more and more popular, and many manufacturers are investing on this technology, especially in the automotive field [3]. The main reasons of their success relate to the higher fill factor, greater thermal conductivity, and higher automation of the manufacturing process compared to conventional random windings [4], [5].…”

“…Some practical solutions have been proposed to reduce AC losses [7]. These include decreasing the total amount of copper in the slot and pushing the conductors towards the slot bottom; increasing the number of conductors, whose effectiveness depends on the frequency range; adopting new winding concepts, such as segmented or asymmetric bar layouts [3].…”

“…However, these would have a significant impact on the manufacturing process, since the asymmetric layout implies the need of hairpins with legs featuring different cross sections to guarantee the change of layer. Alternatively, single leg conductors could be used (I-pins), but this would double the number of welding points [3]. However, these complications relate to conventional hairpin winding manufacturing lines, where copper wires are used to create the hairpin conductors.…”

Analysis and Mitigation of AC Losses in High Performance Propulsion Motors

“…At high operating and switching frequencies, the winding AC losses become more prevalent in electrical motors [5][6][7]. This is especially true in hairpin winding machines [8,9]. However, the focus of this paper contribution is on classical random windings with round wires.…”