Optimisation of Additively Manufactured Hairpin Windings for High Power Density Traction Motors

Abstract

Despite the widespread use of hairpin winding (HW) in electric vehicle (EV) traction motors, several AC loss phenomena hinder its broader application at higher operating frequencies. This paper investigates methods for reducing AC copper losses, focusing on both design approaches and advanced manufacturing techniques, particularly additive manufacturing (AM). A comprehensive analysis of various HW layouts is conducted, evaluating AC copper losses through finite element (FE) and analytical approaches, while considering the effects of circulating currents and short pitching. Detailed analysis of a HW motor is performed to address the influence of magnetic saturation and rotor-magnetomotive force (MMF) on AC copper losses. Moreover, sizing of HW dimensions at a specific operating speed is carried out analytically and validated using FE analysis, with the aim of minimizing high-frequency losses. The potential of AM to enhance manufacturing flexibility and facilitate conductor size optimization is briefly explored. A case study with in-depth optimization is performed to determine the optimal HW dimensions at representative operating points along the torque-speed curve. As a result, the most suitable HW design for EV applications is proposed and benchmarked against results from rigorous optimization processes.