Analytical Approach to Design Hairpin Windings in High Performance Electric Vehicle Motors

This work deals with the analysis and design of a hairpin winding. Such a winding type is more and more used in traction motor of electric and hybrid electric vehicle. It allows a higher slot fill factor in comparison with the traditional round wire windings. This yields a high reduction of the Joule losses, when the motor is required to develop high torque, e.g., during accelerations. However, due to the high cross-area section of such rectangular-shape conductors, the current is non-uniformly distributed in the conductors, and this causes a reduction of the benefit of the higher copper area. In addition, due to the high frequency at the higher speeds, parallel paths are often required. Particular care has to be posed when such parallels are designed, with proper transposition of the wires, to avoid a non uniform distribution of the current in the parallel paths. The motor parameters are computed analytically and then validated by means of a Finite Element analysis. Satisfactory results are achieved. The additional losses are computed according to the conductor geometry and the whole winding connections (parallel paths, transposition, and so on) with a satisfactory precision.