A Comprehensive Design Guideline of Hairpin Windings for High Power Density Electric Vehicle Traction Motors

The rapidly increasing demand on power density levels of electric vehicle (EV) drive systems is pushing the boundaries of traction motor performance. Hairpin windings are becoming a popular option for EV motors due to their reduced dc losses and improved heat dissipation capability when compared to traditional random windings. In this article, a comprehensive design approach of hairpin winding layouts is first presented. The flexibility and limitation of end-winding patterns are thoroughly investigated in terms of basic pin connections, special jumpers, transposition, parallel branches, terminal positions, phase shift, winding pitches, as well as slot-pole combinations. To address the challenge of much reduced practical layout options with increased slot number per pole per phase, two novel hairpin winding designs are proposed. A 160-kW, 18 000-r/min permanent magnet (PM) traction motor featuring the new winding layout with 54-slot, 6-pole is developed using a multidomain design platform, which puts special focus on the conductor size optimization. The advantages of the designed motor are clearly revealed by comparison with the more traditional 48-slot, 8-pole counterpart. Finally, a corresponding stator prototype with the proposed hairpin winding is built to validate its manufacturability.