Design Considerations For High Power Density Traction PM Motors With Hairpin Windings

The automotive industry trend is to push e-axles power density to reduce the weight, maximize the available space and reduce cost of the vehicle. Pushing power density means high mechanical speed and high peak current density. Maximum speeds for traction machines found in the industry are in the range of 12-20 krpm. The trend is to move towards maximum speeds of the traction motor above 20 krpm, in particular for high performance electric vehicles. This paper analyzes the design challenges of selecting the concept design for a high speed traction PM motor and high current density. The study is limited to hairpin winding PM machines for vehicle traction application and with a maximum operating speed above 20 krpm. The trade-off between power density, efficiency and cost is studied analyzing the most relevant pole/slot combinations and rotor topologies considering electromagnetic, thermal and mechanical aspects.