Advanced thermal management in sustainable high-power-density traction motors
Publication Date
July 27, 2026
Creator
Lima Bezerra, Danielly
Abstract
Electric vehicles (EVs) are at the heart of the electric revolution in the transportation sector. Central to an EV is the electric traction motor, where high power density and high efficiency help to minimise energy losses, extend battery life, and increase the driving range.
In this context, hairpin winding technology is a key enabler of high-power-density traction motors due to high slot fill factor, uniform end windings, and automated manufacturing. However, its large conductor cross-sections increase AC losses due to skin and proximity effects, and manufacturing inconsistencies can cause circulating currents, resulting in additional AC losses. Therefore, accurately predicting and mitigating these losses is crucial for improving thermal management in traction machines.
This work proposes and validates an analytical model that enables the rapid calculation of power losses in hairpin windings. It also examines how manufacturing-related conductor misalignment can induce circulating currents, using analytical, numerical, and experimental results. The analytical model is based on the Sub-Domain Model (SDM) and an equivalent electrical circuit formulation, allowing the calculation of power losses in distributed hairpin winding layouts. In addition, validations against the Finite Element Method (FEM) indicate the models’ accuracy across a wide frequency range, with deviations of less than 2%.
On the thermal management side, a hairpin stator is investigated for single-phase oil spray cooling, employing mesh-free Computational Fluid Dynamics (CFD) to calculate the convective Heat Transfer Coefficient (HTC) in the end windings. The results are used as boundary conditions for a steady-state thermal Finite Element Analysis (FEA) to explore the influence of end-winding geometry on spray cooling performance. The findings provide insight into how the hairpin end windings’ geometry can be modified to improve convective HTC, wettability, and minimise temperature gradients in hairpin stators.
At last, a comparative analysis of copper and aluminium windings is carried out to explore trade-offs between efficiency, thermal behaviour, and sustainability. Results show that while copper windings exhibit lower winding power losses, aluminium can achieve competitive performance and stay within the thermal constraints imposed by the insulation materials when paired with advanced cooling, offering an alternative towards a more sustainable, less energy-intensive motor design.
This work advances hairpin winding technology by introducing a fast, high-fidelity analytical model for calculating winding losses, assessing manufacturing effects on circulating currents, optimising end winding geometry for better cooling, and analysing the thermal effects of using aluminium instead of copper in windings. The validated models and practical insights can be used to improve the design and manufacturing of hairpin windings for sustainable high-power-density traction motors.
Item Type
ethesis
Thesis Type
PhD
Supervisors
University of Nottingham, UK
University of Nottingham
University of Nottingham
University of Nottingham
University of Nottingham
Subjects (LC)
Associated Schools / Departments
UoN Repository URI
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