University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

D.Ing. / Transformer design is an art which spans a century. Although the basic transformer has changed little over this period, the challenges that face high frequency power transformer designers today have grown considerably. Increasing frequency and power density and decreasing size and profile are among the most important. Eddy currents, controlling circuit behaviour and minimising losses are important aspects of design, and close attention is paid to heat removal and cooling. Modern transformers are no longer limited to certain shapes and sizes; choosing the topology and optimising the shape is often part of the design process. For each aspect of design, numerous modelling techniques exist for analysing transformer behaviour, with varying degrees of complexity. A common feature of optimisation techniques is the large number of variables and interdependent functions that relate different aspects, from the associated behavioural models, to one another. In this study, this complexity is reduced by integrating the individual analytical models for transformer behaviour. Since a convenient thermal model for high frequency transformers does not exist at present, a new thermal reference model is devised and verified. It is specifically suited to high frequency transformer applications and design, and practical sets of reference data are provided for a few ferrite materials and for copper. Transformer losses are considered next, with special attention given to eddy current analysis techniques. New formulations of eddy current solutions are given, with extensions of the orthogonality principle for skin- and proximity effects and superposition thereof. An investigation of leakage impedance design as a function of frequency scaling follows. The relationship between leakage reactance voltage drop as a function of frequency scaling by dividing a monolithic transformer into distributed elements is considered, and the results are applied to two case studies of a 35kVA transformer for a plasma burner application. A new model, the generic proportionality model, applies the thermal referenCe model to scaling of transformer parameters. A case study is also presented, demonstrating the relationships that exist between design parameters and performance functions. Another generic model, the scant model, is introduced, which integrates the thermal reference model into optimisation of transformer shape. It uses a limited number of functional and form parameters, and is applicable to a wide variety of geometries. Two case studies, demonstrate the effects of varying the shape of a rectangular configuration on derating factors.

M.Tech. / The majority of low income households in South Africa are based in either informal settlements or low cost housing. These households use paraffin as their primary fuel source for cooking and heating. The objective of this study was to identify design factors that should inform paraffin stove design. These factors include the design process, the problem context, the problem identification, the understanding of stove safety and interface issues through laboratory testing, understanding the user through user testing and developing recommendations from the research of these factors. The four main problems associated with paraffin usage as identified in this research are unsafe stoves, fires caused by these appliances, the high levels of emissions given off by these appliances in small enclosed households and issues related to the storage of paraffin that leads to the accidental ingestion of paraffin. The outcome of this research includes a set of findings and recommendations which were compiled to inform the design of future paraffin stoves. Finally, this study reflects on a commercial design process that was used to develop a series of design solutions for the Paraffin Safety Association of South Africa’s paraffin stove design competition in 2005.

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High voltage RF systems are used to accelerate proton beams for nuclear physics experiments. The acceleration process shapes the proton beam into a train of narrow pulses with the same period as the RF. This bunched beam structure is used to separate and identify secondary particles that are produced when the proton beam is directed at a "target". An RF controller for a system that separates secondary particles was built. Control of high power RF cavities that operate near resonance is discussed. The emphasis is on developing a control model for resonant systems and building a control system based on hardware and software modules that can be easily configured for different RF systems. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Magnetic bearings have recently begun to be employed in rotating machinery for vibration reduction, elimination of oil lubrication problems and prevention of failures. This thesis presents an analysis and design of an experimental model of a magnetic suspension system. The magnetic bearing, its control circuit and the supported object are modeled. Formulas are developed for the position and current stiffness of the bearing and the analogy with a mechanical system is shown. The transfer function is obtained for the control and experimental results are presented for the double pole one axis magnetic support system. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

A refractory self-aligned gate fabrication process for gallium arsenide MESFETs has been developed and applied to a sample and hold circuit. The process has been shown to reduce the parasitic end resistance of MESFETs which can be a limiting factor in their microwave performance. A mask set was designed to be compatible with Cascade Inc. probes which allowed on chip microwave measurements to be made. Usable gain was measured up to 18GHz on FETs and 5GHz on buffer amplifiers with the microwave probes at the Communications Research Centre in Ottawa Ontario. The microwave probes were also used to test sample and hold operation. The maximum tested sampling rate was limited by the test equipment to 250 MHz. The fabrication process included a plasma etch for producing an undercut 'T' gate structure for self-aligned ion implantation. A method of sputtering a thermally stable alloy of TiW refractory metal was developed to provide suitable Schottky contacts to GaAs. It was found that a rapid thermal anneal following the self-aligned implant maintained suitable TiW/GaAs Schottky characteristics and yielded MESFETs with reduced end resistance when compared to those fabricated by the more conventional selective implant process. A technique was developed to reduce the gate resistance of self-aligned MESFETs using an evaporated metal overlayer. Also, procedures for fabricating airbridges using a single evaporation and Metal-Insulator-Metal (MIM) capacitors using silicon nitride as the dielectric were developed. The effect of gate resistance on the microwave performance of the self-aligned MESFETs was investigated by modeling with the EEsof Inc. microwave software package, Touchstone. The modeling showed that self-aligned MESFETs are capable of giving greater high frequency gain than are selective implant devices with the same design geometry. The operation of the sample and hold circuit was simulated using a version of SPICE that included the Sussman Fort GaAs MESFET model. The simulations showed that the sample and hold could be used for gigahertz sampling. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The techniques of computer modeling and simulations are used to develop a design procedure for greenhouse solar heating systems. In this study a flexible computer program was written based on mathematical models that describe the various subsystems of the solar heating system that uses the greenhouse as the solar collector. Extensive simulation runs were carried out for predicting system thermal performance, and subsequently correlations were established between dimensionless variables and long term system performance. The combined greenhouse thermal environment - thermal storage model along with the empirical relationships and the values of constants approximated in the simulation yielded reasonably accurate computed results compared to observed data. The computer model was then applied to predict the system behaviour using long-term average climatological data as forcing functions. A parametric study was made to investigate the effects of various factors pertinent to greenhouse construction and thermal energy storage characteristics on system performance. The key performance indices were defined in terms of the 'total solar contribution' and the 'solar heating fraction'. Correlations were developed between monthly solar load ratio and total solar contribution, and between total solar contribution and solar heating fraction. The result is a simplified design method that covers a number of alternative design options. It requires users to obtain monthly average climatological data and determine the solar heating fraction in a sequence of computational steps. A crop photosynthesis model was used to compute the net photosynthetic rate of a greenhouse tomato canopy; the result may be used to compare crop performance under different aerial environments in greenhouses equipped with a solar heating system. This research program had attempted to generate technical information for a number of design alternatives, and as design optimization of greenhouse solar heating is subject to three major criteria of evaluation: thermal performance, crop yield and cost, recommendations were put forward for future work on economic analysis as the final step required for selecting the most cost effective solution for a given design problem. / Graduate and Postdoctoral Studies / Graduate

This thesis deals with bridge design as an important part of road design and layout. Bridges frequently dominate roads and railways, and are, in many cases, a prominent feature of the landscape. Discriminating selection of the type of bridge and material to be used, having regard to technical and aesthetic requirements is therefore essential. Road construction and bridge design are both applied arts in landscaping, and should be considered as such throughout the planning sequence. Since the main thrust of this thesis is directed toward the aesthetic and engineering aspects, no attempt has been made to include overall economic analyses or details of construction; however, to indicate the basic nature of the engineering principles and to demonstrate appropriate dimensions of bridge components, calculations and sketches of a few bridges are included. Various types of bridges are evaluated and discussed in terms of their accordance with modern environmental requirements. The design of the new bridge across the Alouette River at the U.B.C. Research Forest is taken as a particular case study, the analyses of this crossing showing that thoughtful selection of both bridge and location can not only enhance the landscape, but also improve route conditions. Engineers should blend their talents with nature so as to create a harmonious landscape. / Forestry, Faculty of / Graduate

At the time of publication of this thesis little if any reliable technical data was available on the design, construct ion and operation of gas fired pottery kilns. A few publications have some information but for the most part very little information on the proportional relationships of the various' aspects of gas kiln designs are available. If one was to use only the information available in previous publications, inefficient, unsafe and illegally built kilns could easily be manufactured. Students, teachers and various public institutions are finding it necessary to design, build and operate gas kilns to fulfill the education of their students or fully explain the traditional methods of combustion firing and its unique results. It becomes more apparent that guidelines are necessary so that an efficient, safe and inexpensive kiln can be built and utilized without hampering the usefulness of a variety of designs available. This search for information about kiln design and construction had two main directions, the author consulted authorities having jurisdiction over gas kilns in British Columbia and Alberta and secondly he built and tested kilns using the data collected. These two sources of information were compared in relevant locations to publications available up to publication time. For the most part the investigation into kiln operation comes from informal instruction from a number of successful kiln builders and operators and provincial gas inspectors. It has been the researcher's finding that there is a very strong indication that the parameters given are a reliable and useful guide to safe, efficient and pollution controlled kiln design. The main parts of kiln design seem to be dimensional and dynamically interrelated and the parameters of design have shown a very high improvement in efficiency and pollution control which are important benefits. The dynamics of kiln design are only preliminary and broad in this thesis. Much more could be done with closer testing using more elaborate equipment and controls and with the guidelines used from this paper and further investigation even further improvements in design parameters may improve the efficiency and safety of future kilns. This thesis is designed to serve as a handbook which is the result of applied research. The thesis is set out in three parts. A brief essay establishing a rational for having a gas kiln, the model for designing a gas fired pottery kiln, and lastly examples of research and kiln firing logs from kilns designed using the model. Methods of construction, brick laying application of insulation and arch construction are not covered in this paper as they are well covered in the Olsen and Rhodes books. (see bibliography) / Education, Faculty of / Graduate