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Василевський, Володимир Валентинович. "Прогнозування строку служби силового трансформатора за допомогою комплексної моделі технічного стану целюлозної ізоляції." Thesis, Національний технічний університет "Харківський політехнічний інститут", 2019. http://repository.kpi.kharkov.ua/handle/KhPI-Press/39553.
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Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.09.01 – електричні машини й апарати. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2019 р. Дисертацію присвячено удосконаленню математичних моделей для прогнозуванню залишкового ресурсу силового трансформатора та техніко-економічного обґрунтування стратегії його технічного обслуговування шляхом розробки комплексної моделі технічного стану целюлозної ізоляції. Запропоновано комплексну модель технічного стану целюлозної ізоляції, яка складається з математичної моделі формування реального ресурсу трансформатора на етапі його виробництва та моделі витрати ресурсу целюлозної ізоляції силового трансформатора на етапі експлуатації. Розроблено математичну модель вологообміну в системі целюлозна ізоляція – трансформаторне масло у взаємозв'язку з іншими математичними моделями, які описують стан трансформатора в експлуатації. Проведено аналіз впливу проведення технічного обслуговування силового трансформатора (зокрема, сушіння активної частини) на ресурсні характеристики целюлозної ізоляції. Виконано моделювання витрати ресурсу трансформатора для різних стратегій технічного обслуговування. За допомогою аналізу результатів моделювання обґрунтовано необхідність урахування проведення технічного обслуговування при розрахунках залишкового ресурсу і моделюванні витрати ресурсу ізоляції в експлуатації. Отримав пода-льший розвиток розрахунковий метод визначення скорочення строку служби ізоляції за рахунок корегування відомої формули інтегралу старіння шляхом більш точної інтерполяції вихідних даних, що використовуються для побудови залежності швидкості старіння від вмісту вологи в ізоляції. Вперше запропоновано математичні моделі для оцінки впливу етапу виробництва на призначений ресурс, які відрізняються урахуванням недосконалості засобів контролю і стохастичності процесу зміни ресурсу в ході технологічного процесу.Thesis for granting the Degree of Candidate of Technical sciences in speciality 05.09.01 – Electric machines and apparatus. – National Technical University "Kharkiv Politechnical Institute", 2019. The thesis is dedicated to the improvement of mathematical models for forecasting the residual lifetime of a power transformer and the feasibility study of its maintenance strategy by developing a complex model of cellulose insulation technical condition. The complex model of the cellulose insulation technical condition, which consists of a mathematical model of the transformer's real resource formation at the stage of its production and a model of the resource consumption of the power transformer's cellulose insulation during the exploitation phase, is proposed. The mathematical model of water exchange in the system of cellulose insulation - transformer oil in the interrelation with other mathematical models, describing the condition of the transformer in exploitation is developed. The analysis of the effect of maintenance of power transformer (in particular, drying of the active part) on the characteristics of cellulose insulation is carried out. The transformer resource consumption modeling for different maintenance strategies is executed. The simulation justified the need to take into account the maintenance in the calculations of the residual resource and the modeling of the insulation resource consumption in operation. The calculation method for determining the reduction of insulation's lifetime was further developed by adjusting the known formula of the integral of aging by more accurate interpolation of the original data used to construct the dependence of the rate of aging on the moisture content of the insulation. For the first time, mathematical models for assessing the influence of the production stage on the assigned resource, which differ by the imperfection of control and stochasticity of the process of resource change during the technological process, are proposed.
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Green, Alexander Nicholas Michael. "Modulatory charge recombination dynamics in dye-sensitive solar cells." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428505.
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FernaÌndez, Oscar. "Electromechanical characterisation of PP EMFi." Thesis, Bangor University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412567.
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Phillips, Neil William. "Application of high temperature superconductors to electric drives." Thesis, Cardiff University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521460.
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Zulu, Ackim. "Flux switching machines using segmental rotors." Thesis, University of Newcastle Upon Tyne, 2010. http://hdl.handle.net/10443/1070.
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Flux switching machines (FSM) employing a segmental rotor have field and armature systems on the stator and a presentation of an unexcited rotor with isolated segments. The single-tooth winding arrangement on the stator provides a potential for material and energy savings. The principle for producing bipolar flux in the armature stator teeth relies on the natural switching of the armature tooth flux, accomplished by the moving segments of the rotor. Three phase configurations have been studied, from conception and design to construction and testing, with field excitation provided by either a field winding or permanent magnets (PM). Flux switching machines have shown characteristics that are peculiar when employing a segmental rotor, significantly affecting the symmetry of the induced armature EMF waveform and parity of magnitudes of the positive and negative torques. For three phase operation, six topologies are feasible when employing a 12-tooth stator and two other topologies may be produced on a 24-tooth stator. An optimum topology on the 12/8-configuration and another proof-of-principle topology on the 12/5-configuration, using field-windings and permanent-magnets, have been designed and constructed, while applying modern practices and considerations for manufacture. The characteristics of FSMs employing a segmental rotor, initially predicted by finiteelement (FE) modelling, have been verified by measurements. The FSM employing a field-winding is found to have a specific torque output which is similar to the conventional switched reluctance motor and still substantially higher than that of the synchronous reluctance motor. Although the PM adaptation of the FSM produces specific torque output which is nearly twice that of the wound-field FSM and about 64% that of an equivalent permanent-magnet synchronous motor (PMSM) with surface or insert magnets, accounting for the usage of the magnets reflects its specific torque output to be about 1.48 times higher than the PMSM. Although the FSM is operated as an AC machine with sinusoidal three-phase currents, its dq-equivalent representation shows significant differences from that of the conventional AC machine. In the prediction of the performance, it is found, in both the wound-field and PM configurations, that the dq model is more dependable if the coupling dq inductance is taken into account.
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Pinguey, Edwin. "On the design and construction of modulated pole machines." Thesis, University of Newcastle Upon Tyne, 2010. http://hdl.handle.net/10443/993.
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This thesis presents two designs for modulated pole machines from concept through to validating prototypes, each comparing favourably with other modulated pole machines. The key feature to these designs is that they employ novel fabrication techniques which are realisable in low cost manufacture without compromise in performance. This is achieved by reviewing the specific properties of soft magnetic composite and laminated steel. Each material was then utilised in such a way as to take best advantage of its distinguishing properties leading to the development of novel fabrication and construction techniques. The designs are each presented in three stages. Firstly the development of the concept is presented and the use of finite element simulation to reach a design worthy of construction is documented. The development of fabrication techniques for the various parts is then presented along with the assembly into a working single phase prototype. Finally testing and comparison of results with simulated and other existing published designs is presented.
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Miti, Gideon Kalebe. "Control of brushless D.C. motor drives." Thesis, University of Manchester, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557126.
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Silva, Peththadurage S. Narendra De. "Analysis of N-phase induction machines using a generalised decoupled vector space theory." Thesis, Heriot-Watt University, 2006. http://hdl.handle.net/10399/2151.
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A generalised analysis method for N-phase induction machines is presented. The Nphase system is analysed using 2N degrees of freedom. A new conceptual view of a multi-phase system using an N-dimensional vector space has been developed. It is shown that such an N-dimensional vector space can be decoupled into 'h(N+PJ independent two dimensional vector planes, where if N is odd, p=l, otherwise P=O. Each vector plane is shown to be the combination oftwo positive and negative sequence components ofthe same phase order. Each vector space is shown to be independent and can be controlled separately by an N-phase inverter. Each inverter state is shown to have a location in every vector space. A vector control strategy has been realised for developing independent vectors in decoupled vector spaces, resulting in the desired voltage waveforms at the inverter outputs. A five-phase induction motor is designed, and constructed as an integral part of five-phase drive system. A five-phase decoupled vector space controller is implemented in a fixed-point digital signal processor and the practical five-phase inverter based drive system validates the proposed decoupled vector space theory. The analysis of multi-phase machines during imbalanced. electrical operation is considered using decoupled vector space theory. It is shown that each independent vector in the decoupled vector spaces produces unique flux distributions in an N-phase AC machine, but only one vector space develops fundamental rotor linked flux and thus fundamental torque. The interaction of decoupled vector spaces with winding harmonics is developed in order to analyse the effects of unbalanced currents in a i' practical induction motor. It is shown that torque is produced only by the primary vector space currents in a sinusoidally wound machine. The additional freedom available from auxiliary vector spaces can be used to compensate for imbalance caused by faulty machine phases. It is shown that there exists 2N-3 degrees of freedom for an N-phase system of fluxes of an N-phase machine with a floating neutral. These degrees of freedom can be used to compensate for the phase imbalance created by opencircuited inverter legs. The machine can still be fluxed to produce rotational power. At the pre-fault to post-fault transition, the current vectors of the operational phases are reoriented to produce a rotating fundamental flux. A five-phase induction motor drive system demonstrates the performance for the loss of one and two phases. Harmonic winding function generated flux interaction is analysed and interpreted in terms of a five-phase motor with single and two phase loss.
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Cotton, Ian. "Lightning protection of wind turbines." Thesis, University of Manchester, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.578062.
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Issa, Rihman H. "An investigation of efficient control strategies for a PWM inverter driven induction motor." Thesis, Loughborough University, 1987. https://dspace.lboro.ac.uk/2134/11783.
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Recent developments in power electronics switching devices have led to significant improvements in AC drives which, coupled with the obvious advantages of squirrel-cage induction motors, have generated a customerled demand for an increase in AC drive performance. This thesis describes the design and construction of a 3-phase pulsewidth modulated inverter using gate turn-off (GTO) thyristor switching devices, which drives a 0.75 kW 3-phase squirrel-cage induction motor. The inverter control circuit comprises a purpose-built large-scale integrated circuit, which generates the 3-phase pwm drive signals and allows the output voltge and frequency to be varied independently. When operating in open-loop, the drive system is capable of reverse operation, and the maximum rate of acceleration and deceleration of the motor may be controlled. Compensation for resistive voltage drop is provided when the motor is running at low speed. An analogue closed-loop proportional-integral-derivative speed controller is described, and for efficient operation under both no-load and on-load conditions torque feedback is also included. This provision both reduces the no-load losses in the motor and improves the torque-speed characteristic under load conditions. The improved closed-loop performance also includes power factor correction when the motor is lightly loaded,.together with an automatic boost to the motor voltage when loads are applied at low speed. A comparison is made between the performance of the analogue system and a digital real-time control implemented using a microcomputer. A series of computer programs are presented which simulate the performance of the drive system and which are suitable for running on the University mainframe computer. The programs enable the effects of the modulation technique and the inverter frequency on the pwm inverter steady-state output to be studied, and the performance of the induction motor to be investigated. Throughout the work, the theoretical predictions are supported by considerable experimental results.
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Saleh, Kamel Subhi. "Sensorless Control of High Power Induction Motors Using Multilevel Converters." Thesis, University of Nottingham, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523161.
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Zakaria, Khairul Parman. "The Application of Simulated Annealing for Condition Monitoring in Induction Motors." Thesis, University of Newcastle Upon Tyne, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506610.
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Leaver, Mark Edward. "High-speed drives for consumer products." Thesis, University of Newcastle Upon Tyne, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612619.
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The aesthetic design and thus market appeal of consumer products is limited by the size and weight of the universal or brushed DC motors that they typically employ. As many similar products are displayed for sale side-by-side, it is the aim of any manufacturer to ensure that their product stands out from the rest either in terms of performance, features, aesthetics or ergonomics. This thesis presents the research, design, development and product deployment of two high-speed brushless machines that remove the limitations and restrictions on machine design imposed by mechanical commutation and demonstrates the significant advantages to product design and performance that can be gained by moving away from traditional brushed motor technology. The first machine design is a 3-phase 100,000rpm permanent magnet machine which has been coupled with a high-ratio gearbox to provide a unique drive system for use within a 700W mains-powered electric drill. The research shows that for a given power rating, an optimal motor speed exists for size minimisation of a motor/gearbox transmission system when the design of the corresponding gearbox is also considered. Following the presented optimisation method, a new drive system has been designed that is half the size and 80% lighter than the existing drive, leading to an easy-to use tool that fits within the housing of a much smaller cordless drill product. The second machine is a single-phase, bifilar-wound, 32,000rpm permanent magnet machine for directly driving the impeller of a 200W cordless vacuum cleaner. This lowcost machine demonstrates that a bifilar winding with simple two-switch drive can be successfully applied at this power rating. When compared to the original machine, the presented design shows an axial length reduction from 59mm to 20mm and a 29% reduction in mass. The high speed of the new motor increases the vacuum performance of the product by 70% when using the existing vacuum impeller.
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Smith, Andrew Neil. "Speed Sensorless Induction Motor Drives : A Comparison." Thesis, University of Newcastle Upon Tyne, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506428.
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Wu, Xu. "Development of high temperature PEMFC and high temperature PEMWE." Thesis, University of Newcastle Upon Tyne, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555981.
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Polymer electrolyte membrane fuel cells (PEMFC) and polymer electrolyte membrane water electrolysers (PEMWE) are promising electrochemical energy conversion devices. This thesis describes research carried out on high temperature PEMFC and PEMWE. High temperature (> 100 QC) operation is one of the most topical research trends of PEMFC and PEMWE, because of the operational and kinetic advantages it can provide. In this research, an anhydrous solid electrolyte, Sb-doped SnP207 was prepared and characterized. The synthesis parameters, microstructure, and conductivity of Sb-doped SnP207 were studied. The Sbo.2Sno.gP207 exhibited good conductivity (0.01-0.l S cm") in the temperature range 100-300 QC, and was initially applied in PEMFCs at intermediate temperatures (200-300 QC). Research into development of polymer acid complex membranes for high temperature PEMFCs, including phosphoric acid and sulphuric acid - doped polybenzimidazole membranes, was also carried out. The maximum power density of high temperature PEMFCs achieved was 0.5-0.7 W cm-2. For high temperature PEMWEs, firstly, Sn and Ir stabilized RU02 nanopartic1es were synthesized and studied as catalysts for the oxygen evolution reaction (OER). Iro.7RUo.302 nanopartic1es were found to be the most stable and active catalysts for OER. Research to develop a catalysts coated membrane (CCM) method for PEMWE membrane electrode assembly (MEA) fabrication is described. A high performance PEMWE was developed by studying fabrication parameters of the CCM method and optimizing electrode compositions of MEAs. High temperature (> 1 00 QC) PEMWE was eventually realized, using a perfluorinated silica composite membrane. The voltage achieved at 1 A cm-2 current density of PEMWE was 1.51 V at 140 QC and 4 bar pressure. The final part of this thesis describes work on catalyst support materials, which are essential for reducing noble metal loading in PEMWEs. Although the costs of PEMFCs and PEMWEs are still high, which is due to noble metal catalysts and expensive membranes, high temperature operation (> 100 QC) can help both devices be more competitive for energy conversion applications.
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Ng, Kong. "Electromagnetic losses in brushless permanent magnet machines." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.579745.
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Abdelhamid, F. S. aleh. "Detection and Diagnosis of Electrical Faults in Induction Motors using Instantaneous Phase Variation." Thesis, University of Manchester, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520502.
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Norton, Matthew Savvas Harry. "Investigation of a novel, building-integrated photovoltaic concentrator." Thesis, University of Reading, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555862.
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This thesis examines the performance of a building-integrated 10X photovoltaic concentrator proposed within the EU Framework-5 CONMAN project. The concentrator behaves as a window or skylight, allowing diffuse light to enter the building, whilst using mirrored slats to capture direct sunlight for conversion to electricity. The underlying logic is that by building integration, the proposed design can be economically and environmentally preferential to standard building-mounted PV panels in situations where the EU Energy Performance of Buildings Directive applies. A survey of building-integrated concentrator systems was conducted and indicated this to be a novel system. A technique of pressing to form the parabolic mirrors amenable to mass production was developed, in addition to a novel tracking system. Tests on BP LSBG cells indicated an approximate cell efficiency of 19% at the concentration levels expected. These design features in combination indicated that the cost of the system could be kept reasonably low, and a detailed design, called the 'Venetian Blind' was developed, constructed and tested. A biaxial model of the collector was developed, and a Visual Basic programme developed to simulate its output. Good correlation was found between the system model and the test data. When used to simulate annual output for the system in climates typical of the south of Spain, the model indicated that the system produced electricity at an approximate module cost of $8/equivalent Wp when not building integrated, and $5/equivalent Wp when building integrated. The system incurred longer energy payback periods than flat plate PV, but not substantially so when building integrated. Overall, 1 the optimised system is projected to produce electricity for 0.3$/kWh at good sites. Note that the system's potential contributions to-the passive solar gain of a building are likely to be very substantial, in addition to its electrical output.
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Salman, S. "Parameter estimation of synchronous generators on isolated systems." Thesis, University of Aberdeen, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.593388.
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The design of electrical power systems on offshore platforms involves ensuring the safe and reliable operation of the systems. These criteria prompted the need for performing short-circuit studies and fault level calculations. Using the results obtained from these studies together with the load data, the switchgear rating and fault rating of the switchboard can be determined. This study will aid the designer in determining both transient and substransient reactances of the generators, whereby the transient reactance is used in studying the effect of starting a large motor such as a compressor or a pump and the substransient reactance is used in short circuit studies. The generators parameters are therefore essential in the determination of circuit breaker setting, switchboard ratings and the starting capability of motors. These factors have prompted research into methods for determining the parameters of synchronous generators. The tests approved by the British Standards which are usually employed by manufacturers, however suffer from a number of disadvantages such as the possibility of damage to the generator windings as a result of the sudden three phase short circuit test. On the other hand some of these tests such as the d.c. standstill decay test are quoted as 'unconfirmed testing methods'. This study is therefore aimed at developing a method whereby the parameters of synchronous machines can be estimated directly from the on-line voltage and current waveforms. The study starts by determining the parameters of two salient pole generators using the conventional methods. This is used later to establish the accuracy of the proposed method. The effect of varying the generators parameters on voltage and current waveforms is then analysed, leading to the introduction of a method using only three simple tests. The accuracy and reliability of the method is demonstrated using the software simulator SABER. Finally the new parameter estimating technique is used to determine saturated parameters of the two laboratory generators for different field excitations.
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Sayers, Laura R. "Synthesis and characterisation of M-doped titanium dioxide for the potential application in electrochemical devices." Thesis, University of Surrey, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.566823.
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The chemistry of systems intended to produce metal-doped, nanostructured oxide materials containing titaniumffV) has been investigated. Manganese and iron were chosen as cheap, sustainable metal atom dopants with a view to possible use of product materials in electrochemical devices. In particular, the aim was to enhance electronic conductivity and to introduce psudocapacitance for investigation in supercapacitor devices. Previous literature in this area was found to be misleading; products of earlier synthetic studies have been incompletely characterised, with solid products being assumed to be single crystalline phases and metal atom contents being assumed on the basis of hypothetical doping levels rather than being determined analytically. Electrochemical properties of product materials in electrode films were determined in this study via use of EIS, CV and galvanostatic charge- discharge techniques. Conventional sol-gel and micro-emulsion synthetic methods were undertaken with the view to control of product particle sizes and yields for single phase, Mn-doped titaniumfl V) oxide (ideally within the anatase structure). Other than for the pure binary oxides of manganese or titanium, the products obtained were mixtures of oxides rather than single phases, with titaniumfl V) in the rutile polymorph within the I mixed-phase products. "Doped" product materials produced by the emulsion method showed no improvements in conductivity or specific capacitance when compared with a standard anatase (undoped) sample. The mixed-oxide materials produced by the sol-gel method, containing Mn02, had enhanced conductivities but no improvement in specific capacitance. Single-phase, anatase structured, Mn-doped titanium dioxide materials, were prepared using the continuous hydrothermal synthesis (CHS) method. The maximum amount of Mn successfully incorporated into the .anatase structure was found to be approximately 8%wt, as determined by AAS, ICP-MS and SEM-EDX analytical methods; high Mu-content resulted in phase segregation and irreversibility within cyclic voltammograms, as evident in observation of an oxidation peak but no reduction peak. The highest recorded specific capacitance value for these samples was that for the CHSMn008 sample (theoretical composition Tio.92Mno.os02), with a value of 4.5 F g'l (oxide specific surface area, 34.8 m2 g·l). This compared to a similarly prepared anatase (undoped) material with a specific surface area of 48.6 m2 g'l and a specific capacitance of 2.5 F g·l. No correlation between specific surface areas and specific capacitance values was observed, but the BET-determined ·specific surface areas were for powdered samples whereas capacitances refer to composite electrode films. Chapter 1 Introduction • ", The initial eHS product materials displayed no improvement in conductivity, but p H-adjusted synthesis led to samples (denoted CHS MnKOH) with higher conductivities consequent on higher Mn contents, and these samples also had the highest specific capacitance values. In view of the success of the eHS method in producing Mn-doped anatase materials, it was also used to synthesise Fe-doped titaniumffV) oxides. The products were a range of single phase materials, but syntheses aimed at high Fecontents led to mixtures, Ti02 + Fe oxides + Fe2Ti05; the maximum amount of Fe incorporated whilst still maintaining a pure single phase product was approximately 7%wt. The conductivity of these materials showed marked improvement relative to the standard (undoped) anatase sample, comparable to those for eHS MnKOH samples, but the Mn-doped samples had higher specific capacitances than Fe-doped counterparts . . The highest specific capacitance values recorded were between 25 and 32 F g'l, regardless of dopant (MnlFe) and/or phase purity, and were associated with a high specific surface area or a high concentration of "dopant" within the sample. 1
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Edwards, S. "Fault diagnosis of rotating machinery." Thesis, Swansea University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636771.
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In this thesis, topics of importance to the fault diagnosis of rotating machinery in the power generation industry have been addressed, including a review of the relevant literature and an overview of the associated rotordynamics modelling and analysis techniques. For faults involving rotor-stator interaction it has been shown that the inclusion of torsion in mathematical models used for rotor-stator contract analyses can have a significant influence on the dynamic behaviour of the system. A 3 degrees-of-freedom model based on the Jeffcott rotor was developed and, for physically realistic systems, it was shown that very different results were obtained when including torsion, compared to when torsion was neglected, as has generally been the case in the past. An identification method for estimating both the excitation and flexible support parameters of a rotor-bearings-foundations system has been presented. Excitation due to both mass unbalance and a bent rotor were included in the analysis, which has been verified both in simulation and experimentally. The method has great practical potential, since it allows balancing to be performed using data obtained from just a single run-up or run-down, which has obvious benefits for field balancing. Using this single-shot balancing technique in experiment, vibration levels were successfully reduced by as much as 92% of their original levels. A bent rotor has been accurately identified in both simulation and experiment. It was also shown that including bend identification in those cases where only unbalance forcing was present in no way detracted from the accuracy of the estimated unbalance or foundation parameters. The identification of the flexible foundation parameters was generally successful, with measured and estimated parameters matching very closely in most cases. The identification method was tested for a wide range of conditions and proved suitably robust to changes in the system configuration, noisy data and modelling error.
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Hewings, D. B. "Probabilistic modelling of load and harmonic distortion in an A.C. traction system using an object-oriented approach." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637271.
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As a means of reducing over-design and gaining greater insight into the operation of dynamic systems, probabilistic methods have evolved as a extremely important design tool. This has been true of power system design in general over the past thirty years, and probabilistic methods are now used in the design of overhead line supports, fault-clearing plant and the assessment of load demands. However, the application of probabilistic methods to the design and analysis of traction power systems has been relatively limited. These systems involve not only the electrical characteristics of the power system, but also the mechanical aspects of an electric railway, and produce moving, frequently changing electrical loads. The electrical system itself is not easily analysed, since modern locomotives incorporate power electronic switching drives, conventionally analysed in the time domain, whilst the supply is analysed in the frequency domain. This study details the development of an object-oriented traction system model, which can incorporate both the time and frequency representations into a single integrated model. This integrated model is then used as the basis of investigation into the probabilistic characteristics of the electrical load and harmonic distortion produced by the traction system. The study shows that an object-oriented approach may be applied to switching-circuit analysis, and that a combined frequency- and time- domain analysis may be easily implemented with this type of system. The probabilistic simulations show for the first time that the load and harmonic characteristics of an a.c. traction system do not fit known parametric models, and are in fact highly dependent upon the operational characteristics of the traction system, e.g. route profile and timetable.
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Anagren, Y. N. F. "Real-time sliding mode control of a brushless DC motor." Thesis, Swansea University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.635778.
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Conventional DC-brush motors have been used extensively as variable speed drive systems due to their linear characteristics, which result in easy speed control. However, AC drives become an attractive alternative to their DC counterparts in various industrial applications. This is due to the recent developments in both power electronics and microelectronics technology. Brushless permanent magnet motors combine the advantages of brush-DC motors and AC motors. Therefore, a tremendous effort is carried out to utilise this type of electrical drive in high performance industrial applications. A robust control design, having the feature of insensitivity to parameter variations and load torque disturbances, is highly demanded in many modern variable drive systems. The recent advancements in producing fast microprocessors and high switching power devices enable the digital implementation of advanced control schemes. One of these schemes is the sliding mode control technique, which has been implemented successfully in a wide variety of industrial applications. A real-time high performance low cost speed control of brushless DC motor drive is developed in this thesis. The controller design is based on the theory of sliding mode control. The developed drive system is further improved by including a 'chattering reduction' in the controller design. The developed speed control system is assessed through both simulation and practical studies. The practical implementation is achieved using the Intel 80C196KC single chip microcontroller and all the required tasks are carried out solely through software, which has the flexibility for future development. Extensive results at different operating conditions are given throughout the thesis to prove the validity of the developed scheme.
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Buckley, Alison Jayne. "The attachment of corona ions to aerosol particles near high voltage powerlines." Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505750.
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Corona ions emitted from overhead AC high voltage powerlines have been investigated and their effect on atmospheric aerosol charge assessed for potential health effects evaluation. To quantify the influence of the powerlines on the environment, ground-level measurements have been made upwind and downwind of ten lines in South West England.
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Gordon, B. M. "Small induction motor drives." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599532.
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Domestic appliances represent very cost conscious applications for drives where the emphasis is on achieving the optimum compromise between cost and performance. The requirements placed on a domestic appliance drive are so radically different from those demanded of an industrial drive, that a detailed re-evaluation of all the constituent sub-units of the drive must be undertaken. Domestic appliances are produced in large volumes so the use of a special arrangement or custom components can be justified if an overall benefit can be demonstrated. The work presented in this dissertation is concerned with small drives which are suitable for domestic appliances. A study of the optimal number of phases for current and possible future power electronic construction methods is presented and their suitability of domestic appliance drives considered. Comparisons based on material utilisation and the quality of the air gap flux waveform are presented. With the power electronic technology available two and three phase drives were found to be the best compromise between cost and complexity, and several drives of each type were built to provide experimental evidence on the performance of each alternative drive topology proposed. The experimental results obtained from the different drives built are related to the conclusions of work on inverter topology and phases number.
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Ahmed, Saeed Mohamed. "Investigations into the improvement of a single phase permanent magnet brushless DC motor." Thesis, University of Leicester, 2011. http://hdl.handle.net/2381/10114.
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The work presented in this thesis is aimed at improving single phase permanent magnet brushless DC motors; including their operation, design, efficiency and smoothness. Three main areas were identified and researched for further improvement. As a precursor to this work, a detailed literature study related to each area is also presented. The first of these areas concentrates on the improvement of the open circuit torque for a single phase BLDC motor. The open circuit torque is not only due to the slot openings, but is also contributed by the uneven airgap which is conventionally used to solve starting problem. The aim is to enhance the starting torque at alignment positions and attenuate the torque ripple between null points where the back EMF is non-zero. The improvement of the open circuit torque was investigated in two stages. In the first stage the open circuit torque due to the slot openings was reduced, and in the second stage the focus was on enhancing the open circuit torque contributed from the uneven air gap topology with minimum ripple. The second area of investigation was to devise a new encoderless control method for a single phase BLDC motor. A detailed analysis on the derivation of the method is presented. The method has been validated both analytically and numerically. The third area of investigation was the creation of a new non-complex phase advance control method. The details of the analytical simulation and practical implementation are presented. The method has been validated experimentally and it was shown that the experimental results agree well with the analytical predictions.
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Abdelsalam, Ahmed Kadry Ahmed. "Medium-voltage PWM indirect vector controlled induction motor drive with a long motor feeder." Thesis, University of Strathclyde, 2009. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21996.
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This thesis studies two types of medium-voltage (MV) vector controlled PWM induction motor drives for long motor feeder applications, namely voltage source and current source based drives. As rectifiers and inverters are the main elements in any drive system, both are investigated, but with more emphasis on the inverter side. MV PWM current source rectifiers (CSR) usually use selective harmonic elimination as a modulating strategy which provides good harmonic reduction at a low switching frequency. The rectifier performance does not meet the IEEE 519 regulation concerning harmonics injected into the supply current. Two solutions are presented. First, line side passive filters for harmonic mitigation and power factor improvement. Second, shunt active power filters based on p-q theory, with a step-down high-frequency transformer. The presented solutions are compared to highlight their features and limitations. Several topologies can be used for PWM CSRs. A detailed study of the selection criteria for PWM CSR semiconductors is presented based on losses, physical size, and number of series devices. Utilization of a PWM voltage source inverter (VSI) drive system in long motor feeder applications leads to motor terminal over-voltage problems. Surge filters are used to mitigate this phenomenon. Among the various types of filters, the motor terminal RC filter and the inverter output RLC filter are common. A detailed investigation is presented of the effects of these filters on the VSI drive system. PWM current source inverter (CSI) drive systems are characterised by their motor friendly voltage behaviour and controlled short circuit capabilities. Therefore, a proposed indirect vector controlled PWM CSI drive is presented for long motor feeder applications. Performance comparison between PWM VSI and CSI drive systems for long motor feeder applications is performed to clarify features and limitations of each system. Motor voltage is needed for speed estimation but measurement of voltage/speed is impractical for long motor feeder drives. A model reference adaptive system speed estimator is proposed with a novel remote motor voltage calculator that depends on the inverter voltage and feeder parameters. Offset and drift problems that occur during the flux estimation process are solved by a proposed DC-offset eliminator.
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Norman, Rosemary Anne. "High-performance current regulation for voltage-source-inverter-fed induction motor drives." Thesis, University of Bradford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.514187.
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Goodwin, Roy C. "Decision-support software for the design of high-frequency wound-components." Thesis, University of Edinburgh, 1991. http://hdl.handle.net/1842/12043.
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The architecture and control strategies of computing environments able to provide decision-support, together with software selection, are described. In the area of engineering design, the need to provide both a knowledge base and a database, and direct communication between the two, is recognised as an essential pre-requisite to the successful development of decision-support software. The role of expert systems in developing and maintaining the knowledge base, and factors influencing the choice of expert system, are discussed. An integrated software network in which to build computer-aided design tools is described and fully realised. The network is based on Crystal, a commercially-available expert system shell, and Lotus 123, which provides data support and management. The expert system can interrogate directly the database via a custom interface while a second interface allows the user direct access. Library facilities are also available to permit the filing of designs produced by the system. Assessment of the interface is achieved by comparing it with a commercially-available database interface. Finally, using the software network developed, two rule-based expert decision-support systems for the design of power transformers and inductors carrying direct current, operating at frequencies up to 100 kHz, are developed. The relevant component-design methodology, and the scope and operation of the design software, are explained.
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Evans, James Paul Owain. "Development of a 3-D x-ray system." Thesis, Nottingham Trent University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393246.
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Chen, Fang. "Sliding-mode control and observer design for high performance control of an induction machine." Thesis, Heriot-Watt University, 2002. http://hdl.handle.net/10399/397.
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Masoud, Mahmoud Ibrahim. "Decoupled control of rotor torque and rotor electric power in a salient pole, synchronous machine." Thesis, Heriot-Watt University, 2003. http://hdl.handle.net/10399/389.
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Jordan, Nicholas. "Protection co-ordination within the D.C. traction network." Thesis, London South Bank University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434419.
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Allan, Malcolm. "Hardware/software strategies for the DC brushless motor." Thesis, Glasgow Caledonian University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282722.
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Lamine, Adoum. "Vector control of induction machines considering the stray load losses." Thesis, Liverpool John Moores University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.436561.
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Gerada, Christopher. "Dynamic field models of electrical machines and their control systems applied to performance enchancement and fault tolerance." Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417213.
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ShaÌneÌŒl, Martin. "Investigation of rotor cooling in salient pole electrical machines." Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412119.
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McLaren, Victoria Leah. "A study of rock salt superstructure oxide phases and their possible applications in lithium ion batteries." Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398376.
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Li, Fei. "A non-intrusive method for the determination of overhead line configuration and the derivation of system voltage waveforms." Thesis, University of Strathclyde, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435127.
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Darroman, Yann. "Reducing the energy consumption of battery-powered products by the use of switched-mode techniques." Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398535.
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Masood, Tariq. "Improvement of voltage and power flow control in the GCC power grid by using coordinated FACTS devices." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589638.
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This work presents HVDC/FACTS control device implementation framework in the Gulf cooperative council’s countries. It comprises of five layers of FACTS control devices (STATCOM, SSSC, UPFC, HVDC and centralized/De-centralized Control). This five-layer architecture is designed in order to configure and produce the desired results; based on these outcomes, GCC power system network control and operational problems can be identified and addressed within the control architecture on the GCC power grid. In the context of power FACTS-FRAME, this work is to identify and determine a number of power systems operational and control problems which are persistent on the GCC power grid e.g. poor voltage quality (SAG-Swell), poor load flow control, and limited power transfer capacity issues. The FACTS-FRAME is configured and synthesized by integrating multiple FACTS control devices (STATCOM, SSSC, UPFC) in parallel at different locations on the GCC power grid in order to meet stringent power system control and operational requirements with improved power transfer capacity, controllability and reliability. The mathematical models are derived to indentify and determine operational constraints on the GCC power grid by incorporating real-time and estimated data and the acquired desired results. Herein, FACTS-FRAME is designed to handle distributed computation for intensive power system calculation by integrating multiple FACTS devices on multiple networks within the GCC power network. Distributed power flow algorithms are also derived in order to understand and implement centralized and decentralized control topologies as appropriate. The simulation results indicate the feasibility of FACTS devices implementation and their potential benefits under current operating conditions on the GCC power grid.
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Clark, Joanna Helen. "Inorganic materials for energy conversion." Thesis, University of Liverpool, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.569768.
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In an effort to design systems that harvest solar light and convert this into chemical energy, the primary aim of the work presented in this thesis was to develop complex metal oxide materials that were active photocatalysts under visible light. The existing methods for visible light incorporation into photocatalytically active materials are reviewed. Of these, metal to metal charge transfer (MMCT) between bimetallic surface- grafted assemblies was taken as particular inspiration. It was hypothesised that MMCT between metal centres within a bulk complex metal oxide could be similarly applied to yield photocatalytic ally active charge carriers. This approach takes advantage of the stability of bulk systems and the ability to tune the compositions of complex oxide materials. Moreover, it was proposed that MMCT between metal centres located on crystallographically distinct sites of a bulk material would aid charge separation and migration throughout the extended lattice. The optical properties of the RE2 Ti207 (RE = Y, La, Ce, Pr) and Ba2XTizM3015 (X = La, Ce, Pr, Nd, Bi; M = Nb, Ta) series, which include some novel cerium(III) titanates, revealed systematic changes in the electronic structures of these materials. These were rationalised with respect to the energy of Ln 4f states. The proposed electronic structures present the partial achievement of the bulk MMCT hypothesis, with optical transitions from occupied Ce 4f midgap states to the unoccupied primarily Ti 3d conduction band. These Ce3+ /rr" charge transfer materials were inactive photocatalysts, attributed to the presence the Ce 4f-based midgap states that facilitate charge recombination. The double perovskite CaCu3T40IZ, with A-site Cu2+ and B-site Ti4+ cations and whose dielectric properties have been studied extensively in the past, is an ideal candidate for the two site MMCT strategy. Here, the optical and photocatalytic properties, rationalised with the aid of DFT calculations, present the partial achievement of the bulk MMCT hypothesis. Sol-gel derived Pt-CaCu3 Ti4012 is an active photocatalyst toward the visible light photo-oxidation of model pollutants methyl orange (MO) and 4-chlorophenol (4CP). Optical spectra and product analysis show that these reactions proceed via more selective routes than the typical reaction over TiOz P25 under DV light. Interestingly, the products of 4CP photo-oxidation were shown to be dependent on the wavelength of incident light. Cu-doping of BizTiz07 was found to stabilise the pyrochlore structure with respect to the Aurivillius phase Bi4 Ti3012 and to impart significant visible light absorption. Sol-gel derived Pt-BiI.6Cuo.4 Tiz07 photo-oxidised MO under visible light via conventional band gap excitation, as determined by quantum efficiency measurements. In contrast, sol-gel derived Pt-B4 Ti3012 photo-oxidised MO via the excitation of adsorbed MO, and was also active toward 4CP photo-oxidation under visible light. The excitation method, mechanisms and product distributions have been investigated for each of the photo-oxidation reactions presented in this thesis. In particular, the photo- oxidation of MO over some Pt-modified metal oxides has been shown to proceed via excitation of adsorbed MO and not of the semiconductor. Additionally, the mechanism and products of these processes are far more selective than the related DV reactions over TiOz P25, and have been shown to depend to some extent on the semiconductor support.
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Watson, Stuart. "Instrumentation for low-conductivity magnetic induction tomography." Thesis, University of South Wales, 2009. https://pure.southwales.ac.uk/en/studentthesis/instrumentation-for-lowconductivity-magnetic-induction-tomography(62c6312c-5158-45e6-82bf-51b379dfa2f3).html.
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Magnetic Induction Tomography (MIT) belongs to a group of techniques for the non invasive imaging of the passive electrical properties of objects which also includes Electrical Impedance Tomography (EIT). In MIT, arrays of coils are employed to induce eddy currents within an object and to detect the resulting secondary magnetic fields. Conductivity and permittivity distributions are then reconstructed from the collected set of four-terminal transimpedance data. MIT has several potential advantages relative to EIT including (i) errors due to variability of electrode contact impedances and positioning are avoided since the coils in an MIT system are typically rigidly attached to a chassis/screen, and (ii) the magnetic fields employed easily pass through high impedance boundary layers (e.g. the skull in brain imaging applications). Applications of MIT may be broadly divided into two categories: high-conductivity and low-conductivity. The development of MIT for low-conductivity applications (a < 30Sm -1)has been much slower than for highconductivity ones since the conductivities involved are lower, typically by a factor of ~1x107 resulting in much smaller signals and very challenging instrumentation design. The aim of this work was to develop MIT systems with a performance level approaching that required for low-conductivity medical and industrial applications including the detection of haemorrhagic cerebral stroke and the imaging of multi-phase flows in oil pipelines. The specification, design and performance of three novel low-conductivity MIT systems are described and are discussed in relation to the target applications. The Cardiff Mkl single-frequency MIT system was only the second multi-channel MIT system to be constructed, the first low-conductivity MIT system which allowed measurement of both real and imaginary signal components, and provided a higher measurement precision (by a factor of 6) than the previous system, with a phase noise of 17mO for 30ms time constant. A planar array system is described employing a novel coil geometry which provided a very significant reduction in phase noise and drift through the use of coil orientation. Finally, the Cardiff Mk2 multi-frequency system provided an order of magnitude improvement in measurement precision in comparison to the Cardiff Mk1 system with phase measurement precision of 1.1 m0 - 8m0 over 10MHz -0.5MHz, SNR for in vivo human head measurements estimated at 59d.B - 16dB over the same frequency range and phase drift of < 1OmO over periods of up to 12 hours.
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van, der Toorn Gregory Theo. "Investigation of losses in cage induction motors." Thesis, University of Cambridge, 2001. https://www.repository.cam.ac.uk/handle/1810/272003.
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Golightly, Ian Thomas. "Visual control of an unmanned aerial vehicle for power line inspection." Thesis, Bangor University, 2006. https://research.bangor.ac.uk/portal/en/theses/visual-control-of-an-unmanned-aerial-vehicle-for-power-line-inspection(a2a86872-1ee2-4ab4-976a-8019353aca7b).html.
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This thesis describes the investigation into the use of visual servoing to keep an unmanned aerial vehicle (UA V) aligned with overhead electricity distribution lines, in order to use it to inspect them. The UAV would carry cameras in order to capture video footage showing the line's condition. Firstly, the current methods of inspecting overhead electricity distribution lines, line-walking and manned helicopters, are described. A review of visual servoing and the relevant tracking methods is presented. Then a mathematical model of a ducted-fan UAV is developed. Analysis of the image geometry is performed to show how movements of the UAV affect the positions that the overhead lines appear in the images from the UAV's camera. This analysis shows that it should be possible to estimate the UAV's position relative to the lines if two cameras, one pointing forward and one pointing backwards, are used. The design and construction of a laboratory test rig to perform experiments is described. Then the image processing method, based on the Hough transform, used to extract the overhead lines from the image is described followed by the development of a tracker, which makes use of fuzzy logic and a Kalman filter, to track the overhead lines from frame to frame. Experiments are performed to see how well the UAV is able to follow the lines using the laboratory test rig. Finally, conclusions are drawn as to how well the system works as well as suggestions for the future direction of the project.
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Norton, Mark B. "An object oriented approach to electrical machine design." Thesis, University of Bath, 2005. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423486.
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Atallah, Kais. "Iron losses in brushless permanent magnet DC machines." Thesis, University of Sheffield, 1993. http://etheses.whiterose.ac.uk/14941/.
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A closed-loop computer-controlled single-sheet test system has been developed to characterise lamination materials and to measure, the iron loss density under any specified flux density waveform. The system has been 'used to validate predictions from a recently developed theoretical model, for the calculation of the excess loss component associated with domaiQ wall movement, under flux density waveforms typical of those encountered in the stator core of brushless permanent magnet dc motors. In addition, an improved expression for the calculation of the iron loss density component, from measured 71 and 7!vectors, due to rotatio~ in non-purely rotating flux conditions, has been derived. A simple analytical model from which the airgap flux density and spread of magnet working points can be determined and which accounts for the effects of curvature for radial-field permanent magnet machines has been developed and validated. The model has been coupled to an analytical technique for the prediction of the open-circuit flux density waveforms in different regions of the stator core, and has subsequently been employed for the prediction of the open-circuit iron loss. In order to predict the iron loss under any specified load condition, a technique which couples a brushless dc drive system simulation to a series of magnetostatic finite element analyses corresponding to discrete instants in a commutation cycle has been developed. It enables the prediction of the local flux density waveforms throughout the stator core under any operating condition, and has been employed to predict the local iron loss density distribution 'and the total iron loss and their variation with both the load and the commutation strategy, Finally, the theoretical findings have been validated against measurements on a representative low power brushless drive system.
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Thian, Boon Meng. "Methods for monitoring the condition of electrical machines fed from variable speed drives." Thesis, University of Aberdeen, 1991. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU034117.
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This thesis is concerned with the investigation and development of methods to monitor the condition of electrical machines, with particular reference to induction machines fed from variable frequency, power electronic supplies. A variety of techniques are suggested whereby the faults that most commonly afflict electrical machines can be identified. Techniques involving the detection and analysis of line current, frame vibration, and leakage magnetic field are proposed and developed to take account of the rich spectrum of harmonics that can be injected through the use of power electronic inverters. To do this it was necessary to produce methodologies that could differentiate between spectral components originating in the inverter, and those produced as a result of the fault. As an extension, two further monitoring techniques were developed in an attempt to provide a fully comprehensive strategem for assessing the health of electrical drives. They are sequence component monitoring, and pulsed eddy current monitoring. The former is an adjunct to those techniques previously mentioned, and when used in combination with them leads to a greater security of diagnosis. The use of pulsed eddy currents is aimed at the on line detection of material failure in the rotating shafts of the machines. For each technique suggested, a comprehensive theoretical basis is provided, and its effectiveness verified by suitable experiment.
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Alrifai, Fayez. "Control of a brushless permanent magnet machine using an integrated torque sensor in place of a rotor position sensor." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/control-of-a-brushless-permanent-magnet-machine-using-an-integrated-torque-sensor-in-place-of-a-rotor-position-sensor(33c96f6b-f8d6-4bab-9e79-d96b975e9fa3).html.
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The work presented in this thesis proposes the use of measured torque feedback from an integrated, low cost surface acoustic wave (SAW) torque transducer in place of a position sensor to control brushless permanent magnet (BLPM) machines. The BLPM machine closed loop control requires knowledge of the rotor position to control stator current and maximum torque per ampere. The electrical position feedback to control the phase current requires a position sensor or position sensorless technique. Position sensors such as absolute encoder or resolver are needed for position information, in the absolute encoder, an accurately patterned disk rotates between a light source and a detector giving a unique digital output signal for every shaft position. However, each bit in the digital world represents an independent track on the encoder disk, resulting in a complex and costly sensors. Brushless resolvers operation is based on inductive coupling between stator and rotor winding. The resolver with its resolver to digital converter also gives precise absolute position information, but again the cost is often prohibitive. So the disadvantages of the position sensors are the added cost and size to the machine. The position sensorless techniques for the BLPM machine are based on obtaining position from the terminal voltages and currents based on estimating the back electro-magnetic force (EMF), flux-linkage or inductance which from position can be estimated. The disadvantages of the back-EMF and flux-linkage techniques are (1) that they behave poorly at zero and low speed (2) behave poorly for load disturbances since load torque is estimated from machine parameters which can change. The inductance techniques work at zero and low speed, however the disadvantages are (1) in a surface mounted machine there is no saliency so any variation of winding inductances with rotor position arises from magnetic saturation; (2) the back-EMF dominates the rate-of-change in the current; (3) the variation of incremental inductances with rotor position undergoes two cycles per single electrical cycle of the brushless pm machine causing an ambiguity in sensed position; (4) the distortion due to the nonlinearities in the inverter; (5) the load offsets and the noise caused by signal injection. This thesis develops a start-up routine and operation algorithms that enhance the performance of position sensorless control of brushless permanent magnet machines at all speeds, including zero speed, and loads by using a machine integrated, low-cost, SAW torque transducer in place of the rotor position sensor.
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Anpalahan, Peethamparam. "Design and analysis of permanent magnet electrical machines for hybrid electric vehicles." Thesis, Imperial College London, 2007. http://hdl.handle.net/10044/1/7605.
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