Strategies to model and reduce high frequency copper losses in electrical traction machine

Abstract

Nowadays, one of the challenges in transport electrification is the reduction of the components’ size and weight for improving the power density. This is often achieved by designing electrical machines with higher rotational speeds and excitation frequencies. In addition, the converter needs to control the machine over a wide speed range given by the mission profile.
However increase of the electrical frequency presents some drawbacks as well: the losses can increase significantly leading to some thermal fault if not considered at design stage; in addition the use of converters could lead to some fault to the winding insulation materials because of the uneven voltage distribution due to the pulse width modulation, which can cause overvoltage in specific portions of the winding.
With regards to losses, the main components can be identified in iron and copper losses. To reduce the iron losses big investments are needed in term of materials and technology, being possible to reduce them using exotic ferromagnetic materials with a very low thickness, which comes at a cost. Copper losses can be reduced by adopting smart distribution strategies and optimised layouts instead.
In this thesis two main winding types have been investigated in detail: the random distributed wires and the hairpin technology. The first one, is mainly adopted in large volume production lines where the stator’s design is the same for all the batches, where each winding manufactured can present differences in strands distribution because of the non ideal distribution of the wires in the slot. This leads to different winding losses and manufacturing uncertainties. A method to predict the losses of random distributed windings is proposed in this thesis, resulting in a better understanding of the physics behind the phenomena and minimising their estimation errors. This aspect has been experimentally validated by using custom made trial windings and motorettes, representative of real electrical machines for automotive applications. The hairpin winding concept has been investigated, looking at reducing the copper losses occurring at high frequency, common in high-speed applications. An hairpin topology has been proposed and as a result of the work, a peak 28% reduction has been achieved and experimentally validated, with respect to the classical hairpin distribution.

Date of Award	15 Mar 2023
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Giampaolo Buticchi (Supervisor), Christopher Gerada (Supervisor) & David Gerada (Supervisor)