Opportunities for AC Loss Reduction in Metal Additive Formed Hairpin Windings

Rectangular bar, hairpin windings are increasingly being employed in power dense electrical machines, as they offer advantages of low DC resistance, good thermal performance and manufacture consistency. The comparably large section conductors used in hairpin windings are prone to high levels of AC loss, particularly when considering fundamental frequencies approaching or exceeding 1 kHz are now common in power dense electrical machines. Methods used to mitigate AC loss involve either reducing the conductor section, through introducing parallel paths or Litz stranding, or substituting a low electrical conductivity wire, e.g. aluminum. With all these approaches is a trade between AC loss reduction versus an increase in ohmic DC resistance. Advances in metal additive layer manufacture allows for complex 3D winding structures to be formed and near maximum (100% IACS) copper conductivity can now be printed. 3D printing allows for AC loss mitigation measures to be targeted to the active regions of the winding, where it is most needed, thereby minimizing the impact on the overall winding DC resistance. The paper develops a simplified analysis framework that enables the loss improvement of incorporating a 3D printed hairpin winding to be assessed for a target application. An EV propulsion motor case study is used to illustrate the methodology.