The invention of the Rotor Field Oriented Control (RFOC) has made the induction machine (IM) dominate the high performance drives market. Fifteen years later, the Direct Torque Control (DTC) strategy has been introduced to give fast torque and flux control with reduced software and hardware requirements. However, the use of flux, speed, current and three-phase stator voltage sensors to monitor the drive states increase the drive cost and reduce the overall system reliability. The number of sensors can be minimised using estimation. However, estimation at low stator frequency operation suffers from pure integration, stability problems, observablity problems, parameter detuning and inverter non-linearity. Thus, it has been suggested to develop and implement stable sensorless RFOC and DTC drives with stator and rotor resistance estimators that can work at low stator frequency with minimal number of sensors. Thus, two types of model reference adaptive system (MRAS) estimators that do not include pure integration have been adopted. A novel design procedure based on linear control theory has been stated to design stable speed, stator resistance and rotor resistance estimators in various operating modes for individual and simultaneous use. The observablity problem at zero stator frequency operation has been eliminated using high frequency injection. The inverter non-linearity has been modeled and thus the model has been used to compensate the inverter voltage losses. The designed estimators have been employed to realise and implement stable sensorless RFOC and DTC IM drives that work at low stator frequency. Furthermore, the classic DTC with fixed switching frequency suffers from torque ripples, flux ripples, torque control offset and flux collapse at low speed and light load. A novel torque ripple minimisation (TRM) DTC scheme has been proposed to predictively eliminate the torque ripple and reduce the flux ripple and also eliminate the torque offset and the flux collapse. In addition, a novel Space Vector Modulation (SVM) DTC has been proposed as an alternative to the TRM DTC scheme and has shown better performance and less computational time. To achieve successful development of sensorless RFOC and DTC drives which can work at low speeds, well-designed stable estimators are the key factor. This research work has given important contribution towards clear vision to analyse and design stable parameter estimators for RFOC and DTC IM drive. It follows, stable speed and stator and rotor resistance MRAS based on back-EMF estimators have been designed for individual and simultaneous use, following the proposed design procedure. These estimators have been employed to implement a stable sensorless RFOC IM drive for low speed operation that insensitive to parameters variation. The performance of the drive has been investigated extensively using simulations and experimental work. In addition, stable speed and stator and rotor resistance MRAS based on current estimation estimators have been designed for individual and simultaneous use. These estimators have been also used to realise a stable sensorless RFOC IM drive for low speed operation. Simulations and experimental work have been carried out to also investigate the performance of the drive. These stable estimators have been also employed to develop two stable sensorless SVM and TRM DTC IM drives for low speed operation and insensitive to stator resistance. The performance of the drives has been investigated for low speed operation using simulations and experimental work. They have shown excellent performance.

The overall aim of the thesis was to provide a holistic view of the potential for electrical energy generation from harvesting of human mechanical work in the urban environment. This required consideration of a broad range of topics including, energy in people, energy conversion technologies and the activity of people and focussed on floor and door integrated devices. The initial step was to consider the potential offered by an individual through consideration of the flow of energy within people and the potential available for harvesting from single actions on floor and door integrated devices. Secondly the process and technologies available for converting mechanical work into electrical energy were considered with a focus on the efficiency with which this could be achieved. Finally, computer based modelling was carried out to determine the expected energy outputs from a device or system of devices to both determine the maximum achievable values and for various assumption based location scenarios in the urban environment. In addition the economic value and displaced carbon dioxide emissions from the generated energy were considered in terms of replacing grid energy. It was concluded that although significant potential exists in the form of human activity, utilising this potential is problematic for a variety of reasons. Much of the energy expended by people is required to complete actions necessary for survival and everyday life, leaving only a small fraction available for energy harvesting. The efficiency with which mechanical work can be converted into electrical energy was found to vary greatly between technologies. In addition it was found that the energy potential is spread diffusely throughout the built environment, with even the most suitable locations returning only modest energy generation values. As a direct consequence it was highlighted that the cost and embodied emissions of devices must be low if human energy harvesting is to offer any benefits.

Partial discharges (PD) are electrical discharges which occur when the insulation of equipment under high voltage stress starts to break down. As their presence provides early warning of equipment failure, detection and location of PD is important for monitoring/assessing the state of equipment. This thesis evaluates the performance of time-difference-of-arrival (TDOA) algorithms and algorithms for locating PD sources -in three dimensions. The complex nature of the statistics associated with location results of iterative and non-iterative algorithms is demonstrated for the first time. Evaluation of iterative and non-iterative location algorithms performance was completed through simulating a range of PD positions with different antenna arrangements. Analysis demonstrates that ability to determine PD position, and location accuracy, is influenced by the error bound, number of iterations and initial values for the iterative algorithms, and antenna arrangement for both iterative and non-iterative algorithms. A novel approach for selecting adequate error bounds and iteration number, using results of non-iterative methods, is proposed, thus solving some iterative methods dependencies. Regarding noise influence on location performance, results indicate that, when applied to individual TDOA, iterative algorithms can eliminate positions with high noise levels while non-iterative algorithm outputs are greatly influenced by noise. A normality test can be used to improve and quantify the accuracy of possible PD location by assessing confidence levels. Location results depend on signal-to-noise ratio (SNR) in acquired data when using a specific sampling rate and the TDOA algorithm used. Higher sampling rate for data capture does not always provide more accurate location results.

This research is concerned with the problem of network power quality when grid connected systems are used to feed the network distribution grid. A parallel connection of photovoltaic (PV) system is the main interest of study for this research. This type of PV system uses power electronic components such as inverter and current controller that produce harmonics which adversely affect the power quality of the distribution network. Development and simulation of current controller using the proportional resonance (PR) scheme is considered to overcome the harmonic problems in single and parallel PV inverters. This scheme eliminates specific harmonic in the low order part. The control parameter randomisation technique is added to the scheme to produce a more efficient current controller system. Thus, the inverter harmonic performance (inverter output current) is improved. This concept is extended to parallel inverter based systems, where opportunities for harmonic cancellation improve the inverter harmonic performance further. Experimental hardware setup using TMS320F2812 is also developed to verify the promising simulation results.

This thesis explores the development of the Segmental Rotor Switched Reluctance Machine (SRM) to provide electric vehicle traction. This electrical machine, which has a topology distinct from the conventional SRM and has been previously shown to offer enhanced torque density, is selected based on its potential to offer a low cost, sustainable alternative to today’s state-of-the-art electric vehicle traction motors. With the launch, as long ago as 1997, of the Toyota Prius Hybrid Electric Vehicle and of the more recent Nissan Leaf Electric Vehicle in 2010, volume produced vehicle traction drives are an established reality. However hurdles remain in order to reduce the cost of electric and hybrid electric vehicles so that they become cost-competitive with more conventional vehicles. From an electrical machine perspective, one clear cost driver stands out; the rare-earth metals which form the key ingredient in today’s class leading electrical machines. These materials are both expensive (>100USD/kg) and, as was seen in 2011 / 2012, subject to significant price volatility. Equally the mining and refinement of rare-earth materials, such as Neodymium, Dysprosium and Samarium, has been shown to have a much higher environmental footprint than that of the other materials typically used in electrical machines. Beyond the elimination of rare-earths, the thesis looks to further improve the sustainability and cost of the Segmental Rotor SRM. Copper conductors, expensive and difficult to recycle at an electrical machine’s end-of-life, are replaced by more easily recycled aluminium. Aluminium windings are compressed, prior to assembly with the electrical machine, in order to achieve very high fill factors to overcome their relatively low electrical conductivity. Methods are also sought to reduce overall material waste and simplify assembly processes; these include computer based optimisation of the motor structure along with the use of modular manufacturing techniques. With the Nissan Leaf’s Neodymium Iron Boron based Interior Permanent Magnet machine selected as a comparator, an 80kW Segmental Rotor SRM is constructed and tested. The design is shown to have promise and a number of industrially funded follow-on projects are now underway in order to develop the technology further for use in a volume electric vehicle application.

No description available.

The fundamental operation of Solid Oxide Fuel Cells (SOFCs) relies on the liberation of electrons at reaction sites within porous electrodes. These reaction sites, or triple-phase boundary (TPB) points, must be percolated to allow for reactants and products to flow to and from these sites. Due to the fact that electrochemical reactions in composite electrodes are dependent on the presence of TPB sites, a direct link exists between SOFC electrode microstructures and electrochemical performance. Recently, the development of advanced tomography and imaging techniques has allowed for this link to be better understood and quantified. This thesis presents the development of a novel effective conductivity model (ResNet) for 3D composite, anisotropic microstructures in the context of Ni-YSZ electrode characterization. The ResNet model is first used to derive the effective conductivity of simple structures, conductivities of which can be found in the literature. Good agreement was found in this initial study. The model is then used to compute the effective conductivities of more complex synthetic microstructures, comparing model outputs to those given by COMSOL Multiphysics, a commercial modeling platform. It was found that for a sufficiently high resolution, both models converge to the same results. Varying the discretization resolution allowed for an optimum discretization resolution to be determined, based on the mean particle size used for fabrication. The introduction of Volume Elements into the ResNet model is then presented, and the optimum aggregation resolution is extracted from a set of simulations. This allowed for the analysis of a real SOFC anode microstructure to be carried out, and underlined the importance of selecting a microstructure sample of a size that can be considered representative of the entire electrode. After a series of simulations on synthetically generated microstructures, several microstructural parameters are varied to carry out a sensitivity analysis on the effective conductivities and current densities of the microstructures. This analysis yielded an optimum ratio of 7 particles per structure length for microstructure size representativeness. Using the parameters derived from the studies presented in this thesis, the effective conductivities of two experimental Ni/10ScSZ anodes are extracted using the ResNet model and compared to their experimentally determined values. Excellent agreement was obtained, validating the ResNet model and associated work. In a final instance, it was shown that using the ResNet model in the electronic phase in conjunction with the VOF model developed by Golbert et al. does not yield a noticeable difference in current density output when compared to results obtained without using the ResNet. When applied to the ionic phase however, using the ResNet model in conjunction with the VOF model is found to predict as much as 50% lower computed area current densities than when the volume fraction average model is used.

Layered Ruddlesden-Popper (RP) type La_n+1Ni_nO_{3n+1} (n = 1, 2 and 3) oxides have recently been suggested as candidates for solid oxide fuel cell (SOFC) cathodes. However, the transport properties of the higher order (n = 2 and 3) phases have not been well-understood. The aim of this work is to achieve well-defined epitaxial La_3Ni_2O_{7-δ} and La_4Ni_3O_{10-δ} films deposited by the pulsed laser deposition (PLD) technique in order to fundamentally investigate their intrinsic anisotropic properties for SOFC applications. This research involved PLD target synthesis and PLD deposition for these RP materials. The obtained films were evaluated through crystallographic, compositional, surface morphological and microstructural characterisation. Their electrical, oxygen diffusion and surface exchange properties were characterised by 4-point DC van der Pauw and the isotopic exchange depth profile (IEDP) with secondary ion mass spectrometry (SIMS) method. Finally, the surface and interface information were also obtained via SIMS and low energy ion scattering (LEIS) techniques. An effect of target degradation during deposition was found to have significant influence on the microstructural and compositional variation with increasing film thickness. Successful epitaxial growth of the higher order phases (n = 2 and 3) of lanthanum nickelate have been demonstrated by PLD for the first time. The total planar electrical conductivity of these higher order RP epitaxial films exhibits a more promising conductivity value than La_2NiO_{4+δ}. These dense higher order RP epitaxial films enabled the first information about the oxygen diffusion and surface exchange properties along the c-axis to be obtained. Also, an outermost surface structure of LaO-termination, followed by a Ni-enrichment in the sub-surface region for these RP materials was found by LEIS analysis. These studies provide useful information to help the further development of these materials and related RP-phases for the potential SOFC applications in the future.

Since the traditional power grid has been showing incapability of meeting the requirements of modern society, the development and implementation of the smart grid (SG) have been a common consensus among policymakers, business leaders, and other stakeholders. The SG is expected to have pervasive control and provide reliable services by utilizing modern information and communications technologies (ICTs). With the advent of smart grid, a number of technical and procedural challenges has emerged and developing efficient algorithms and effective solutions is increasingly urgent. In smart grid, the machine-to-machine (M2M) communication is regarded as one of the key techniques that allow pervasive control and monitoring. In this thesis, various challenges in M2M applications in SG are investigated. ~Thile sparsity plays an instrumental role in signal processing techniques, which enables the theory of compressive sensing (CS) , this thesis explores the sparse properties in M2M networks and exploits the sparsity in various M2M applications in smart grid.

The combustion engine and fossil fuels have transformed human civilization through access to high densities of energy for transport and electricity. However, as fossil fuel resources decline and issues of climate change grow, alternative sources of energy are required. Fuel cells provide the possibility of clean energy through the use of a variety of fuels. Before widespread use of fuel cells is possible, obstacles in the design must be overcome, the greatest of these is the electrode design. Electrodes require a high activity for the electrocatalytic reactions and a high stability during operation. Typically Pt group metals are required to meet these targets. Control of the deposition of these metals, particularly Pt, is essential for the design of the next generation of fuel cell electrodes. In this project a protocol is developed for the epitaxial deposition of Pt using the galvanic replacement of controlled amounts of electrosorbed H. Control was achieved through the selection of the galvanic replacement potential limits and the use of Pd films (1-10 ML thick) on Au as the substrate. Pd thin films exhibit a well known interaction with H characterised by energetically separated processes: H adsorption and H absorption at lower underpotentials. The galvanic replacement kinetics and the reaction stoichiometry were investigated with electrochemical and the quartz crystal microbalance (QCM) techniques. The deposition on the 2 ML Pd/ Au films showed the expected deposition efficiency (2:1 H to Pt). On 10 ML Pd/Au samples the galvanic replacement of the absorbed H resulted in a higher amount of Pt deposition per growth cycle. Pt film surface composition has been confirmed by X-ray photo emission spectroscopy (XPS) , while scanning tunnelling microscopy (STM) results showed quasi-2D Pt film growth. Surprisingly the Pt-10 ML Pd/ Au films showed more reversible absorption/ desorption behaviour than on the corresponding 10 ML Pd/ Au films. A novel method of retrieving H desorption curves from the combination of open circuit potential(OCP) transients and QCM data was developed. This provided the equivalent of continuous H UPD sweeps during the deposition of Pt, characterising changes in the Pt surface as it forms. From this it was observed that the absorbed H peak remained constant during deposition while the adsorbed H peak increased by 5-7% per replacement cycle after the first replacement. The increase in H adsorbed to the surface was interpreted as an increase in surface area due to nano scale roughening of the surface as Pt was deposited.