Manufacture and Analysis of Compressed Aluminium Stator Windings for Low Voltage Electrical Machines

Abstract

During the transition to a fully electric transportation sector, 48 V Electrical Machines (eMachines), employed in Mild Hybrid Electric Vehicles (MHEV), offer electric capability to enhance
the fuel efficiency of petrol and diesel powered vehicles. Compared to high voltage eMachines
used in fully electric vehicles, the low voltage 48 V eMachine provides cost and regulatory reductions, both during manufacture and throughout its service life. In addition, the 48 V MHEV
architecture offers performance benefits including start-stop functionality, power assistance and regenerative braking capabilities, while supplementing the existing 12 V onboard electrical system.
Often positioned as an integrated starter generator, the operating demands of a 48 V eMachine
require high torque for engine startup, as well as high speed, high efficiency operation during
vehicle drive modes, in a constrained volume. This places simultaneous demands for high current
capacity, AC loss mitigation and predictable, uniform coil temperatures on the stator winding
design. To meet these demands, this thesis proposes multistranded, transposed and compressed,
concentrated Aluminium coils for a low-cost 48 V eMachine stator winding.
The three main research objectives concern the challenges around fabrication and analysis of this
stator winding. Firstly, creation of a thermally uniform stator winding, which mitigates operational
losses and exhibits low variation amongst the temperatures of its coils during operation. This requires fabrication and selection of coil sets which exhibit low magnitude and low variation in their
AC loss generation characteristics, and high cross-bundle thermal conductivities. Secondly, nondestructive assessment of coil damage; this will enable damage caused during manufacture to be
identified before assembly, reducing the likelihood of early machine failure. Thirdly, improvement
of the accuracy and fidelity of thermal models by characterising key thermal parameters. This will
allow thermal models to incorporate more representative material parameters, in greater resolution,
thereby informing manufacturing and assembly methods and increasing model precision.
The above contributions are incorporated into the manufacture of a 48 V eMachine prototype. The
eMachine is subjected to steady state DC and AC thermal testing, to validate the proposed design
tools and manufacturing methods as effective means of creating a low-loss, thermally uniform
winding.

Date of Award	30 Sept 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Phil H Mellor (Supervisor) & Nick Simpson (Supervisor)