Manufacturing technologies for reduced AC copper losses in hairpin stators: Increasing the efficiency of electric traction machines

Modern electric machines for the main drive of automobiles contain windings made of solid copper conductors, so-called hairpins. Due to the large copper cross-sections, eddy currents occur inside the conductors, which reduce efficiency and range. This paper sheds light on the loss mechanism using the example of a four- and eight-conductor system and provides a manageable analytical estimate for the design phase. To reduce eddy current losses, current stator designs usually reduce the conductor cross-section and increase the number of conductors. However, this also increases the manufacturing effort, as the corresponding number of conductors has to be bent, assembled, twisted and welded. This paper shows a compromise based on a mixed hairpin system, motivated by the calculation results. The proposed hairpin winding combines the reduced eddy current losses of an eight-conductor system with the low manufacturing cost of the four-conductor system. This provides a cost-effective production of highly efficient traction motors. © 2023 The Authors.