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Title: A design methodology for permanent-magnet electrical machines with concentrated modular windings
Author: Baker, James Leslie
ISNI:       0000 0004 5920 4032
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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Electric propulsion provides many benefits when compared to fully-mechanical power transfer. These benefits include increased configurability, efficiency, ease of control and an ability to offer redundancy. The improved fuel-consumption offered by hybrid electric-mechanical propulsion systems is particularly important to the transport sector. Recent governmental and climate-change targets, which have been driven by the depletion of fossil-fuel reserves, place a growing focus on these propulsion and actuation technologies. The demand to electrify existing commercial products burdens manufacturers to develop and mature electrical systems such that they can be produced in high volumes at low-cost. This pressure places a strong emphasis on the adopted design procedure's suitability for a given application and system requirements. A series-hybrid transmission system for a skid-steered vehicle forms the basis of presented work. The thesis design focus is a high-speed, fault-tolerant electrical machine and is purposed to actuate a "steering input" on this bespoke transmission. The electrical machine design requirements are unusual. The physical envelope is unconstrained and the transmission will be designed to accommodate the prototype; however, a compact machine with minimised mass is desirable. A design methodology for modular-wound electrical machines is developed and presented. The method draws upon published work in electro-magnetic and thermal optimisation; however it is specifically tailored to handle a design problem with an unspecified physical envelope. It is shown that a template electro-magnetic design may be generated to produce an optimal initial geometry; this template is subject to a thermal scaling study which ensures the output requirements are satisfied. Sub-assembly testing provides a useful approach for obtaining difficult to model thermal parameters and calibrating 'stray' AC loss effects. The presented methodology requires fewer design iterations when compared to common procedures; furthermore, it reduces the overall design and prototyping costs without incurring a disproportionate increase in computation-time. The research culminates in a prototype 12000 rpm, 40 kW, 12-slot, 10-pole, interior permanent magnet electrical machine. Electrical fault-tolerance is demonstrated utilising a segmented, 3-phase "machine-modular" stator design, comprising of single-layer concentrated windings. The machine stator is constructed with inexpensive solid conductors. With careful consideration of winding conductor placement, reduced AC losses are exhibited which yields a prototype with a competitive power-density. The dominating factor which governs a machine's achievable specific-output is shown to be the stator's thermal characteristics. These characteristics are not only a function of the materials and construction techniques used, but are equally impacted by stator split-ratio and the choice of physical envelope. The presented design method allows these envelope dimensions to be identified and generates an initial design which is close to the global optimum.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available