Emerging Software Defined Networking (SDN) technology has provided excellent flexibility to large-scale networks in terms of control, management, security, and maintenance. On the other hand, recent years witnessed a tremendous growth of the critical infrastructure networks, namely the Smart-Grid, in terms of its underlying communication infrastructure. Such large local networks requires significant effort in terms of network management and security. We explore the potential utilization of the SDN technology over the Smart Grid communication architecture. Specifically, we introduce three novel SDN deployment scenarios in local networks of Smart Grid. Moreover, we also investigate the pertinent security aspects with each deployment scenario along with possible solutions. On the other hand, we conducted experiments by using actual Smart Grid communication data to assess the recovery performance of the proposed SDN-based system. The results show that SDN is a viable technology for the Smart Grid communications with almost negligible delays in switching to backup wireless links.

The learning demands placed on young children by current language organization techniques used to organize language concepts in AAC systems, are high. This influences the ease of learning and the accuracy with which AAC users use their AAC systems. It is therefore important to investigate the way in which children relate to different language organization techniques to better understand the learning demands placed on them in using these techniques. The aim of this study was to investigate the difference between two groups of 4-year old children’s accuracy levels when locating vocabulary in AAC technologies. The study is a replication of a part of the study conducted by Light, Drager, McCarthy, Mellot, Millar, Parrish, Parsons, Roads, Ward and Welliver (2004). Each group of subjects was assigned a specific language organization technique, i.e. schematic and taxonomic grid organization. The children had to locate vocabulary on a dynamic display system, i.e. the Dynamo. This study considered the language organization technique that best reflects the child’s developmental level. Sixteen subjects, 8 in each group, participated in 4 learning and testing sessions and 1 generalization session. The results revealed that there was no difference in the performance of the children in the two groups. This was in accordance with Light et al.’s (2004) results who also observed no difference in the 4-year-old’s performance with the schematic and taxonomic organization techniques. These results were in contrast with the literature on young children’s semantic organization, which illustrates that preschool children tend to use schematic organizations and begin to use taxonomic organizations once they reach school-age. Recommendations for future research are provided. / Dissertation (MA)--University of Pretoria, 2008. / Centre for Augmentative and Alternative Communication (CAAC) / unrestricted

<p>Computational Fluid Dynamic (CFD) simulations often produce datasets defined over unstructured grids with solid boundaries. Though unstructured grids allow for the flexible representation of this geometry and the refinement of the grid resolution, they suffer from high storage cost, non-trivial spatial queries, and low reconstruction smoothness. Rectilinear grids, in contrast, have a negligible memory footprint and readily support smooth data reconstruction, though with reduced geometric flexibility.</p><p>This thesis is concerned with the creation of accurate reconstruction of large unstructured datasets on rectilinear grids with the capability of representing complex boundaries. We present an efficient method to automatically determine the geometry of a rectilinear grid upon which a low-error data reconstruction can be achieved with a given reconstruction kernel. Using this rectilinear grid, we address the potential ill-posedness of the data fitting problem, as well as the necessary balance between smoothness and accuracy, through a bi-level smoothness regularization. To tackle the computational challenge posed by very large input datasets and high-resolution reconstructions, we propose a block-based approach that allows us to obtain a seamless global approximation solution from a set of independently computed sparse least-squares problems. </p><p></p><p>We endow the approximated rectilinear grid with boundary handling capabilities that allows for accommodating challenging boundaries while supporting high-order reconstruction kernels. Results are presented for several 3D datasets that demonstrate the quality of the visualization results that our reconstruction enables, at a greatly reduced computational and memory cost. Our data representation enjoys all the benefits of conventional rectilinear grids while addressing their fundamental geometric limitations.</p>

The entire diploma thesis analyses causes, consequences and repercussions of an electricity grid network blackout and its impact to the respective consumers. Remarkable blackouts recorded since 1965 are briefly described and basic available information is considered. The grid standard fixing measures and electricity delivery priorities are characterized. The thesis also pays attention to entire Czech Republic grid availability and its blackout endurance as well as to its robustness within last several years. Indirect Fukushima event influence to the Czech Republic electricity system is mentioned. The main part of the thesis comprises of four big European grid blackouts causes and consequences, their comparison to each other and to the Dukovany nuclear power plant grid blackout drill scenario. The preventive and standard corrective measures against blackouts are pointed out.

Thesis (PhD (Electrical Engineering))--Cape Peninsula University of Technology, 2019 / Energy systems based on fossil fuel have demonstrated their abilities to permit economic development. However, with the fast exhaustion of this energy source, the expansion of the world energy demand and concerns over global warming, new energy systems dependent on renewable and other sustainable energy are gaining more interests. It is a fact that future development in the energy sector is founded on the utilisation of renewable and sustainable energy sources. These energy sources can enable the world to meet the double targets of diminishing greenhouse gas emissions and ensuring reliable and cost-effective energy supply. Fuel cells are one of the advanced clean energy technologies to substitute power generation systems based on fossil fuel. They are viewed as reliable and efficient technologies to operate either tied or non-tied to the grid to power applications ranging from domestic, commercial to industrial. Multiple fuel cell stacks can be associated in series and parallel to obtain a fuel cell system with high power up to megawatts. The connection of megawatts fuel cell systems to a utility grid requires that the power condition unit serving as the interface between the fuel cell plant and the grid operates accordingly. Different power conditioning unit topologies can be adopted, this study considers a multilevel inverter. Multilevel inverters are getting more popularity and attractiveness as compared to conventional inverters in high voltage and high-power applications. These inverters are suitable for harmonic mitigation in high-power applications whereby switching devices are unable to function at high switching frequencies. For a given application, the choice of appropriate multilevel topology and its control scheme are not defined and depend on various engineering compromises, however, the most developed multilevel inverter topologies include the Diode Clamped, the Flying Capacitor and the Cascade Full Bridge inverters. On the other hand, a multilevel inverter can be either a three or a five, or a nine level, however, this research focuses on the three-level diode clamped inverters. The aim of this thesis is to model and control a three-level diode clamped inverter for the grid connection of a megawatt fuel cell stack. Besides the grid, the system consists of a 1.54 MW operating at 1400 V DC proton exchange membrane fuel cell stack, a 1.26 MW three-level diode clamped inverter with a nominal voltage of 600 V and an LCL filter which is designed to reduce harmonics and meet the standards such as IEEE 519 and IEC 61000-3-6. The inverter control scheme comprises voltage and current regulators to provide a good power factor and satisfy synchronisation requirements with the grid. The frequency and phase are synchronised with those of the grid through a phase locked loop. The modelling and simulation are performed using Matlab/Simulink. The results show good performance of the developed system with a low total harmonic distortion of about 0.35% for the voltage and 0.19% for the current.

The Swedish Tourist Association, STF, is an organization which strives to make the Swedish nature more accessible to people. Since its founding, STF has been a key player in the development of the tourism in the Swedish mountain regions. Today the organization have 44 mountain cabins along the Swedish mountain range, and a majority of the huts are completely off-grid with no other connection to them but hiking trails. To accommodate for the needs of hikers and skiers throughout the year, the huts need electricity for lighting and in many cases cash registers and satellite modems to run small shops selling simple commodities. Many of the huts use solar energy combined with lead acid batteries, but not all of them can make it through the year without the use of a backup gasoline generator. This master thesis analyzes the different energy systems of four huts run by STF and using solar radiance data from PVGIS to calculate whether or not they are self-sufficient throughout the year using only solar energy. In the cases where the huts were found not to be self-sufficient, suggestions on actions that STF could implement to optimize the systems were found. For two out of the four huts, the thesis found that they were not self-sufficient, but after optimizing the energy systems with new energy saving appliances as well as tilting the solar panels between the winter and summer seasons, all four huts were found to be able to reach self-sufficiency.

The way its future power systems are designed will have significant impact on sub-Saharan Africa's (SSA) aspirations to move from low electricity consumption rates to enhance life quality and further increase economic opportunity. At present, Africa is experiencing higher economic growth rates than other continents (including Asia). And so is its need for electric power. However, all too often the options that are chosen are the ones with lowest risk and that require little coordination. In part, this is because region-wide planning, coordination and institutions are in their infancy. “Low risk” power plants typically include oil generators that can be sited close to loads, other fossil fuel power plants, and hydro plants that can easily be connected to the continent’s grid. However, hydropower production has been limited due to changes in weather and climate and socio-economic impacts. Additionally, its potential has also not been reached as large sites are far from adequate grids. A restructuring of the energy system that considers both the potential for increased geographical integration while moving gradually towards more sustainable electricity generation may hold significant promise. This work considers the potential of another renewable technology namely concentrating solar power (CSP) and connecting supply and demand centers via high voltage direct current (HVDC) power lines. Specifically, the focus is on utility-scale solar power generation to supply the needs of growing urban centers of demand. It develops a Geographic Information System-based (GIS) model with a spatial resolution of 30 arc-seconds to calculate the cost evolution of the electricity produced by different technologies of CSP plants and the costs of grid development to selected centers of demand. The results show that major SSA metropolis can benefit from distant CSP economically attractive to compete with inlaid coal-based generation. In 2010, total imports of coal exceeded 1.4 million short tons with consequent economic and environmental costs. Solar towers plants endowed with thermal storage may become a leading technology for smoothing purposes with zero fuel costs. Furthermore, Africa’s vast solar resources are far from urban centers of demand and a transmission system capable to integrate high levels of renewable energy while improving reliability of supply is required. The results of this study point to the importance of SSA centers to rely on a Super Grid approach to take advantage from CSP least-cost potential and to discontinue expensive traditional sources. Overall, solar corridors can integrate with geographically-wide wind and hydro potentials to create clean energy corridors and encourage a transition towards more sustainable energy systems.

Les travaux de recherche présentésdans cette thèse ont été effectués dans le cadred'une collaboration entre Leroy Somer et lelaboratoire de génie électrique et électronique deParis (GeePs). Ils ont pour objectif lessimulations des phénomènes observés en modetransitoire des machines électriques. Cessimulations sont particulièrement orientées parles nouvelles exigences issues du Grid Code pourles alternateurs connectés au réseau.Principalement, deux types de modèles ont étédéveloppés. Le premier se base sur unereprésentation de l’état magnétique de lamachine où chaque flux est exprimé en fonctiondes courants des différentes bobines. Le secondmodèle regroupe les courants en utilisant descourants magnétisants sur les axes d et q associésà des coefficients de saturation pour chaque fluxet simplifie la représentation magnétique,notamment pour la prise encompte du circuit amortisseur. Avec unemodélisation suffisamment précise ducomportement magnétique non linéaire de lamachine, ils permettent de mieux prédire lescourants et le couple électromagnétique lors desdéfauts tels que les creux de tension. Les travauxeffectués présentés dans ce mémoire ont permis,en partant des descriptions des saturationstrouvées dans une machine, de définir desméthodes pour incorporer la saturation dans lesmodèles de type circuit et finalement d’aboutirau choix du modèle non-linéaire pour unemachine électrique donnée. Grâce à un temps decalcul réduit, ils ont aussi conduit à l'intégrationsous Simulink de modèles de la machine et dusystème d'entrainement pour la réalisationd'études de stabilité et pour créer unenvironnement de mise au point de la commandedu système. / The research presented in this thesiswas carried out in the research and developmentproject between Leroy Somer and the Group ofElectrical Engineering of Paris (GeePs). Theirobjective is to simulate the phenomena observedin the transient states of electrical machines.These simulations are particularly oriented bythe new Grid Code requirements for alternatorsconnected to the power network. Two types ofmodels have been principally developed. Thefirst one is based on a magnetic description ofthe machine where each flux is expressed as afunction of the currents flowing through thedifferent machine windings. The second oneregroups the different winding currents by usingthe magnetizing currents on axes d and qassociated to saturation coefficients for eachflux linkage and simplifies the magneticdescription, especially when taking into accountthe damper windings. With a sufficiently precisemodelling of the non-linear magnetic behaviourof the machine, it is possible to better predict thecurrents and the electromagnetic torque underfault conditions such as voltage drops. The workcarried out in this thesis has made possible,starting from the descriptions of the saturationeffects found in a machine, to define methodsfor incorporating saturation into circuit models.Finally, one can make a choice of the dynamicnon-linear model for a given machine. Thanks toshort computation time, it also led to theSimulink integration of the machine andexcitation system models paving the way forstability and control studies.

The purpose of this thesis is to explore the importance of Smart Grid and to conduct a full feasibility analysis of its implementation in Bangladesh. A smart grid is an electric power system that improves grid accuracy and effectiveness by reacting to systemic disruptions proactively. For a developing country like Bangladesh, it is important for both increased electricity generation and to prevent power outage. A basic necessity for individuals and economies is the efficient transmission and distribution of electricity alongside vital energy supplies. The thesis examines and describes the features and economic topology of Smart Grid, as well as potential solutions to Bangladesh's power issue. It also covers the sustainable transmission and distribution of electricity, as well as the integration of communication and smart monitoring technologies of smart grid.

<p>Accurate measurement of surface grids through imaging enables a variety of applications. One important example can be found in automotive manufacturing, where deformed sheet metal surface strains must be validated in safety critical regions, and rapidly measured to correct process variations. This thesis advances machine vision techniques in the context of close-range surface imaging and measurement. Sheet metal surface strain analysis provides a motivating application, but the contributions may be directly transferred to a variety of other machine vision applications where reliable, accurate measurements are required in adverse imaging conditions.</p> <p>Close-range imaging in practical environments presents a number of challenges, primarily relating to depth of field blur and the regional field of view. This thesis contributes to three major components required for close-range optically-based surface measurement. First, an approach for grid line intersection measurement in the presence of significant and varying depth-of-field blur is considered, with a solution based on scale-space ridge extraction. An architecture for acceleration of the computationally intensive algorithm is then developed, and implemented using state of the art graphics (GPU) hardware. Acceleration to camera video frame rates is achieved.</p> <p>The second contribution is a novel approach for interframe motion tracking of uniform gridded surfaces. The algorithm exploits topological structure of the imaged grid pattern, thereby reducing dimensionality of the interframe tracking problem. Intrinsic fiducial measurement is proposed to avoid the need for explicit feature detectors that locate fiducials in the presence of varying size and blur. Close-range interframe tracking is demonstrated, and statistics are presented on the registration objective function.</p> <p>Finally, an approach is considered for camera and hand-eye calibration of a monocular camera mounted to the tool point of a coordinate measuring machine (CMM). Pre-processing algorithms are contributed to prepare close-range gridded image data for the calibration process. Ideal model coordinate points are coherently assigned to detected grid features across video sequences, and grid approximation is performed for highly blurred image frames where reliable features have not been extracted.</p> <p>The contributions of this thesis make significant progress toward enabling video frame rate, close-range, computer vision-based sheet metal surface strain analysis, and other applications where challenging image conditions impede measurement.</p> / Doctor of Philosophy (PhD)