Assessment of AC losses and Torque Density Enhancement in Hairpin Windings for Axial Flux Induction Motors

Hairpin windings stand out as a promising technology that enhances performance of electrical machines in terms of losses, efficiency and torque density. Extensive research has explored the use of hairpin windings in radial flux (RF) machines, such as induction, permanent magnet, and synchronous reluctance motors. Nonetheless, the potential benefits of adopting hairpin windings into axial flux (AF) topologies, such as the high-torque-density AF induction motor (AFIM), have not been addressed in the literature. This paper investigates the feasibility of using aluminum and copper hairpins in AFIMs by developing an analytical model and conducting 3D finite element simulations of a 4-pole machine. The study focuses on AC losses and torque density variations. Results show that a simple AC loss model can be used to estimate skin-effect and proximity-effect losses in AFIM, and that significant torque density enhancements can be achieved at low frequency, surpassing that of RFIM.