Impact of Segmentation and Parallel Welding on Skin, Proximity and Circulating Current Losses in Hairpin Motor Windings

Due to the shift to electric drive trains in the automotive sector, requirements for electric motors in terms of efficiency and power density have increased significantly [1]. As a result, many optimization strategies for stator windings have recently been introduced, which account for a high proportion of overall losses due to copper losses and thus represent a limit to efficiency [2]. The widely used hairpin winding, which has better dc losses due to its high copper fill factors, suffers from its large cross section of ac losses caused by skin and proximity effects, as well as circulating current losses generated by poor transposition of parallel paths, which are necessary to meet the mmf requirements of the motor [1], [3]. To reduce ac losses, the conductor height of the hairpins is reduced and the number of conductors is increased. To ensure correct transposition, new winding layouts must be designed and, due to the higher number of conductors, more welds must be made. Another way to reduce ac losses and at the same time have a simpler layout design is segmented hairpins [4]. Here, the existing layout can be easily segmented and then connected in parallel so that the electromagnetic configuration does not change. If the parallel segments are connected with a single weld the number of welds can also be reduced. On the other hand additional loops for circulating currents are created which can generate additional losses. In this work, a 4 layer hairpin winding was used as a basis and then compared with a conventional 8 layer winding and 2 segmented variants (serial welding, parallel welding) with half the conductor height. The aim is to determine whether, despite the additional circulating current losses due to segmentation, an acceptable efficiency can be achieved in order to exploit the advantages of greater flexibility and fewer welds.2D field circuit coupled FEM analysis showed that although the segmented variants have higher circulating current losses, the overall copper losses are almost the same as in the 8 layer variant. The additional losses of the segmented variants amount to only 0.03 and 0.5% (serial welding and parallel welding) of the overall losses at 16krpm. The ac component can be reduced by up to 50% compared to the 4 layer basis, as in the 8 layer winding. This makes it possible to segment the layer into two parts for the variant under investigation if the additional losses can be accepted. In addition, parallel welding of the segmented conductors can halve the number of weld points. Although the circulating current losses increase by 14 times (from 5W to 67W at 16krpm) compared to serial welding, the reduction of welding spots of the parallel welded variant still has a very small impact on the overall losses and therefore can make use of the reduced manufacturing expense.In the future the simulation of this thesis should also be verified via 3d simulation and an experimental setup by building and measuring the respective variants. Furthermore, the potential increase of fill factor due to the decreased insulation should be investigated.