Segmented Hairpin Topology for Reduced Losses at High-Frequency Operations

Abstract

Nowadays, one of the key challenges in transport electrification is the reduction of components' size and weight. The electrical machine plays a relevant role in this regard. Designing machines with higher rotational speeds and excitation frequencies is one of the most effective solutions to increase power densities, but this comes at the cost of increased losses in cores and windings. This challenge is even more pronounced in preformed windings, such as hairpins, which enable higher slot fill factors and shorten manufacturing cycle times. In this work an improved hairpin winding concept is proposed, aiming to minimize high-frequency losses while maintaining the benefits deriving from the implementation of hairpin windings onto electrical machines. Analytical and finite element models are first used to assess the high-frequency losses in the proposed winding concept, namely the segmented hairpin, proving the benefits compared to conventional layouts. Experimental tests are also performed on a number of motorettes comprising both conventional and proposed segmented hairpin configurations. Finally, these experimental results are compared against those collected from motorettes equipped with random windings, demonstrating the competitiveness of the segmented hairpin layout even at high-frequency operations.

AC losses reduction in Hairpin Windings produced via Additive Manufacturing

“…For these preliminary FEM evaluations, an electrical machine, with series connected conductors of the same dimensions (classical configuration), designed for automotive applications is taken as benchmark. The most relevant stator features are reported in Table IV [8], including the dimensions of the hairpin conductors. The machine has been analysed by means of 2D time harmonic simulations with sinusoidal current source, using a FEM-based software package, i.e.…”

“…Asymmetric hairpins, which feature a variable cross section along the stator slot as reported in Fig. 1, have shown promising results in terms of loss reduction [8]. 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.…”

On the AC Losses in the End Conductors of Hairpin Windings

“…This, in turn, also causes an uneven distribution of the Joule losses, which tend to increase from the slot bottom to the air gap. Considering the above, several studies have focused on the modelling and reduction of AC losses [8]- [11], both through analytical and numerical approaches, sometimes also corroborated by experimental measurements. In this context, recent findings in hairpin technologies have demonstrated that the main AC losses reduction techniques include:…”

“… adoption of variable cross sections, through the use of asymmetric or segmented slot conductors [11], [13]. These solutions consist of having thinner conductors near the air gap and larger ones at the slot bottom.…”

Investigation of Resistivity Impact on AC Losses in Hairpin Conductors

“…It has been shown that the conductors near the air gap are the most subjected to AC effects (most of all proximity losses due to leakage flux lines) [7]- [9]. For this reason, some research has been focused on how to specifically decrease losses in these more critical conductors, for example with the adoption of variable cross sections or the subdivision of the conductor near the air gap into parallel sub-conductors [10]- [13]. The common denominator is provided by a smaller radial dimension of one or more conductors near the air gap.…”