Dissertations / Theses on the topic 'Grid'

In recent times, with the development of renewables, the concept of micro-grid emerged, representing a novel bottom up power distribution organization. The micro-grid can integrate the nearby distributed, and mostly renewable, energy sources, the storage devices and the loads into the grid, with increased efficiency, flexibility and reliability, showing significant economical and environmental benefits. The micro-grid concept can be further scaled down to the range of a single house or small building, and differentiated by a new terminology, nano-grid. The proposal of the nano-grid concept is aimed at simplifying the application scenarios, so that a hierarchical bottom-up power distribution network can be established, where the nano-grid plays the lowest-end role. It can not only operate autonomously, feeding the typical household appliances from the available renewable sources; thanks to the modular smart grid architecture, it can also be conveniently interconnected to other similar units, operating in parallel and harmoniously energizing a larger region in a city, a small-island or a village. In addition, the nano-grid also has the possibility of self-integrating into the utility grid, exchanging power with the mains when needed, thanks to a specifically designed grid interface converter. Referring to the latter, a variety of requirements are defined by applicable standards, in terms of load power quality, grid support functionalities, abnormal condition ride-through and protection means. The realization of the above functionalities is heavily dependent on the control of the grid interfacing inverter hosted within the nano-grid, about which numerous solutions have been proposed in the existing literature. However, few of them can realize all the functionalities simultaneously in a single controller. The target of this dissertation is therefore proposing, analyzing and testing a high-quality, multi-functional control scheme for grid-tied inverters. This goal is reached in three steps: i) a deep literature review, ii) the identification, study and realization of the multi-functional inverter controller, and iii) the implementation of further, higher level functionalities, like the grid-supporting and parallel operation capabilities. Accordingly, the study is initiated from step i), with an overview of existing control strategies and key functionalities of grid-tied inverters. The comprehensive review of a research topic is, in any case, very advantageous to define the state of the art solutions and to evaluate the margins for improvement in the existing technology. In this research case, it allowed to understand that a triple-loop controller structure is the most suitable to achieve high-performance control of the nano-grid electrical system and the most promising as to the capability of implementing multiple interface and protection functionalities jointly. In the second step ii), a large-bandwidth triple-loop controller is proposed, whose implementation is the first contribution of this dissertation. The peculiarity of the proposed controller is the large-bandwidth control of the injected grid current, which brings in many beneficial features. Leveraging on this controller organization, multiple functionalities are later implemented by means of a superimposed flexible mode-transition manager and an auto-tuner, altogether forming a high quality, multi-functional control scheme for grid-tied inverters. This represents the second contribution delivered by this dissertation. Finally, in step iii), the extended scenario of multiple parallel-connected grid-tied inverters is discussed, targeting the realization of distributed grid-supporting functionalities in grid-tied mode and the automatic balanced power sharing in parallel-islanded mode. The final implemented control scheme provides a feasible solution for the forthcoming smart nano-grids and represents the third contribution of this research activity.

Durant els darrers anys el Grid ha sorgit com una nova plataforma per la computació distribuïda. La tecnologia Gris permet unir diferents recursos de diferents dominis administratius i formar un superordinador virtual amb tots ells. Molts grups de recerca han dedicat els seus esforços a desenvolupar un conjunt de serveis bàsics per oferir un middleware de Grid: una capa que permet l'ús del Grid. De tota manera, utilitzar aquests serveis no és una tasca fácil per molts usuaris finals, cosa que empitjora si l'expertesa d'aquests usuaris no està relacionada amb la informàtica.
Això té una influència negativa a l'hora de que la comunitat científica adopti la tecnologia Grid. Es veu com una tecnologia potent però molt difícil de fer servir. Per facilitar l'ús del Grid és necessària una capa extra que amagui la complexitat d'aquest i permeti als usuaris programar o portar les seves aplicacions de manera senzilla.
Existeixen moltes propostes d'eines de programació pel Grid. En aquesta tesi fem un resum d'algunes d'elles, i podem veure que existeixen eines conscients i no-conscients del Grid (es programen especificant o no els detalls del Grid, respectivament). A més, molt poques d'aquestes eines poden explotar el paral·lelisme implícit de l'aplicació, i en la majoria d'elles, l'usuari ha de definir aquest paral·lelisme de manera explícita. Una altra característica que considerem important és si es basen en llenguatges de programació molt populars (com C++ o Java), cosa que facilita l'adopció per part dels usuaris finals.
En aquesta tesi, el nostre objectiu principal ha estat crear un model de programació pel Grid basat en la programació seqüencial i els llenguatges més coneguts de la programació imperativa, capaç d'explotar el paral·lelisme implícit de les aplicacions i d'accelerar-les fent servir els recursos del Grid de manera concurrent. A més, com el Grid és de naturalesa distribuïda, heterogènia i dinàmica i degut també a que el nombre de recursos que pot formar un Grid pot ser molt gran, la probabilitat de que es produeixi una errada durant l'execució d'una aplicació és elevada. Per tant, un altre dels nostres objectius ha estat tractar qualsevol tipus d'error que pugui sorgir durant l'execució d'una aplicació de manera automàtica (ja siguin errors relacionats amb l'aplicació o amb el Grid). GRID superscalar (GRIDSs), la principal contribució d'aquesta tesi, és un model de programació que assoleix els
objectius mencionats proporcionant una interfície molt petita i simple i un entorn d'execució que és capaç d'executar en paral·lel el codi proporcionat fent servir el Grid. La nostra interfície de programació permet a un usuari programar una aplicació no-conscient del Grid, amb llenguatges imperatius coneguts i populars (com C/C++, Java, Perl o Shell script) i de manera seqüencial, per tant dóna un pas important per ajudar als usuaris a adoptar la tecnologia Grid.
Hem aplicat el nostre coneixement de l'arquitectura de computadors i el disseny de microprocessadors a l'entorn d'execució de GRIDSs. Tal com es fa a un processador superescalar, l'entorn d'execució de GRIDSs és capaç de realitzar un anàlisi de dependències entre les tasques que formen l'aplicació, i d'aplicar tècniques de renombrament per incrementar el seu paral·lelisme. GRIDSs genera automàticament a partir del codi principal de l'usuari un graf que descriu les dependències de dades en l'aplicació. També presentem casos d'ús reals del model de programació en els camps de la química computacional i la bioinformàtica, que demostren que els nostres objectius han estat assolits.
Finalment, hem estudiat l'aplicació de diferents tècniques per detectar i tractar fallades: checkpoint, reintent i replicació de tasques. La nostra proposta és proporcionar un entorn capaç de tractar qualsevol tipus d'errors, de manera transparent a l'usuari sempre que sigui possible. El principal avantatge d'implementar aquests mecanismos al nivell del model de programació és que el coneixement a nivell de l'aplicació pot ser explotat per crear dinàmicament una estratègia de tolerància a fallades per cada aplicació, i evitar introduir sobrecàrrega en entorns lliures d'errors.
During last years, the Grid has emerged as a new platform for distributed computing. The Grid technology allows joining different resources from different administrative domains and forming a virtual supercomputer with all of them.
Many research groups have dedicated their efforts to develop a set of basic services to offer a Grid middleware: a layer that enables the use of the Grid. Anyway, using these services is not an easy task for many end users, even more if their expertise is not related to computer science. This has a negative influence in the adoption of the Grid technology by the scientific community. They see it as a powerful technology but very difficult to exploit. In order to ease the way the Grid must be used, there is a need for an extra layer which hides all the complexity of the Grid, and allows users to program or port their applications in an easy way.
There has been many proposals of programming tools for the Grid. In this thesis we give an overview on some of them, and we can see that there exist both Grid-aware and Grid-unaware environments (programmed with or without specifying details of the Grid respectively). Besides, very few existing tools can exploit the implicit parallelism of the application and in the majority of them, the user must define the parallelism explicitly. Another important feature we consider is if they are based in widely used programming languages (as C++ or Java), so the adoption is easier for end users.
In this thesis, our main objective has been to create a programming model for the Grid based on sequential programming and well-known imperative programming languages, able to exploit the implicit parallelism of applications and to speed them up by using the Grid resources concurrently. Moreover, because the Grid has a distributed, heterogeneous and dynamic nature and also because the number of resources that form a Grid can be very big, the probability that an error arises during an application's execution is big. Thus, another of our objectives has been to automatically deal with any type of errors which may arise during the execution of the application (application related or Grid related).
GRID superscalar (GRIDSs), the main contribution of this thesis, is a programming model that achieves these mentioned objectives by providing a very small and simple interface and a runtime that is able to execute in parallel the code provided using the Grid. Our programming interface allows a user to program a Grid-unaware application with already known and popular imperative languages (such as C/C++, Java, Perl or Shell script) and in a sequential fashion, therefore giving an important step to assist end users in the adoption of the Grid technology.
We have applied our knowledge from computer architecture and microprocessor design to the GRIDSs runtime. As it is done in a superscalar processor, the GRIDSs runtime system is able to perform a data dependence analysis between the tasks that form an application, and to apply renaming techniques in order to increase its parallelism. GRIDSs generates automatically from user's main code a graph describing the data dependencies in the application.
We present real use cases of the programming model in the fields of computational chemistry and bioinformatics, which demonstrate that our objectives have been achieved.
Finally, we have studied the application of several fault detection and treatment techniques: checkpointing, task retry and task replication. Our proposal is to provide an environment able to deal with all types of failures, transparently for the user whenever possible. The main advantage in implementing these mechanisms at the programming model level is that application-level knowledge can be exploited in order to dynamically create a fault tolerance strategy for each application, and avoiding to introduce overhead in error-free environments.

The term Vehicle-to-Grid (V2G) refers to the technology that enables a bidirectional power exchange between the electric grid and the batteries of plug-in electric vehicles (PEV). V2G technology can be a key element of the intelligent network, which may use the batteries of the vehicle as a system of local storage. The vehicle battery may contribute to the stability of the grid and to meeting the energy demand, especially in peak hours. A PEV needs a bidirectional charger to implement V2G, and, consequently, the studies regarding their design, functionality and efficiency are of the utmost interest. This thesis describes the state of art of these chargers and discusses some aspects of a bi-directional converter and some case studies related to this topic. The main objective of this work is to develop the design and the control algorithms of a bidirectional battery charger with capability to charge the battery of a PEV and simultaneously to act as an active filter for the supply line. After the first introductory chapter, the second chapter reports the terminology used in this field of research. Several smart strategies for charging, approaches for the implementation of the battery chargers for PEVs and the recharging standards are briefly described. The analysis of different types of charger is detailed in chapter three. The conventional battery chargers (CBC) with front-end formed by a diode rectifier, battery chargers with power factor correction (PFC), bi-directional battery chargers (BBC), and integral battery chargers (IBC) are considered. In chapter four, definitions are given of the electrical power in non-sinusoidal conditions, together with some examples of the inadequacies of the classical power theory in describing non-linear phenomena that occur during the operation of a power system. The fifth chapter presents the basic concepts of the theory of instantaneous active and reactive power (also known as p-q theory) applied to the compensation of non-sinusoidal systems. Definition of real, imaginary and zero sequence power are introduced and it is shown how this theory makes it easier to understand the phenomena caused by non-sinusoidal voltages or currents. The theory is particularly suitable for the design of a battery charger when it is seen as a power conditioner. Chapter six is devoted to the basic concepts of shunt active filters. They can perform different types of functions, such as the compensation of current harmonics generated by nonlinear loads to prevent their propagation in the network. The compensation algorithm based on powers defined in reference  is very flexible and therefore the theory of instantaneous power has been considered as the basis for the development of the control system of active filters. Some examples of compensation described in the previous chapter were simulated and the results have been included. In chapter seven, sizing of the power devices that constitute the battery charger is considered in relation to the various auxiliary services that it can provide. The power electronic switches, the coupling inductors and the other passive components have been sized in voltage and current. In chapter eight it is considered a charger that supplies its load and simultaneously compensates for non-linear loads connected nearby. These additional features in terms of power conditioning were quantified in order to determine the capacity of a battery charger that is formed by given active and passive components to support the network acting as an active filter. In the ninth chapter the filter inductances of a battery charger are sized for a specific case study in which it is required the capability to recharge the battery and to inject active power in the network, both in the case of single-phase and three-phase connection. Evaluation of the ripple current is an important requirement for the design of inductors. Therefore a precise calculation was made of this magnitude both in the case of a battery charger connected to the single phase grid and operating according to the PWM technique, and, in the case of connection to the three-phase grid, operating according to the technique SVM. In chapter ten a case study is considered regarding the design of an LCL filter. Chapter eleven contains a theoretical study of resonant controllers. They solve the problem posed by the conventional PI controllers that, when used for the control of alternate quantities as it occurs for the currents of a DC/AC converter, are not able to cancel the steady state error due to the finite gain at the operating frequency. Instead, a resonant controller has a gain ideally infinite at the operating frequency and thus ensures a zero steady-state error. The effectiveness of the resonant regulators has been verified by means of simulations. Chapter twelve deals with the regulations regarding connectors, charging modes and ways of connecting the PEV chargers to the grid. They are intended to define a charging procedure common to all the PEVs and to all the charging infrastructures, whether public or private.
Il termine Vehicle-to-Grid (V2G) si riferisce alla tecnologia che permette uno scambio di potenza bidirezionale tra la rete elettrica e le batterie dei veicoli elettrici di tipo plug-in (PEV). La tecnologia V2G può essere un elemento chiave della rete intelligente, che può utilizzare le batterie dei veicoli come un sistema di accumulo locale. Le batterie dei veicoli possono contribuire alla stabilità della rete e a soddisfare la domanda di energia soprattutto nelle ore di punta. Un PEV ha bisogno di un caricatore bidirezionale per implementare il V2G, e, di conseguenza, gli studi riguardo il loro progetto, la funzionalità e l'efficienza sono del massimo interesse. Questa tesi descrive lo stato dell’arte di questi caricabatteria e tratta alcuni aspetti di un convertitore bidirezionale e alcuni casi di studio relativi a questo argomento. L'obiettivo principale di questo lavoro è di sviluppare il progetto e gli algoritmi di controllo di un caricabatteria bidirezionale con capacità di caricare la batteria di un veicolo plug-in e contemporaneamente di agire come filtro attivo nei confronti della linea di alimentazione. Dopo il primo capitolo introduttivo, nel secondo capitolo viene riportata la terminologia usata in questo campo di ricerca. Vengono anche brevemente descritte diverse strategie intelligenti di ricarica, gli approcci per la realizzazione dei caricabatteria dei PEV e gli standard di ricarica. L’analisi dei vari tipi di caricabatteria viene approfondita nel terzo capitolo. Sono considerati il caricabatteria tradizionale (CBC) con front-end costituito da un raddrizzatore a diodi, il caricabatteria dotato di correttore del fattore di potenza (PFC), il caricabatteria bidirezionale (BBC), e il caricabatteria integrale (IBC). Nel capitolo quattro vengono date le definizioni della potenza elettrica in condizioni non sinusoidali assieme ad alcuni esempi delle inadeguatezze della teoria classica della potenza nel descrivere fenomeni non lineari che si verificano durante il funzionamento di un sistema di potenza. Nel quinto capitolo sono presentati i concetti di base della teoria potenza istantanea attiva e reattiva (nota anche come teoria pq) applicata alla compensazione di sistemi non sinusoidali. Vengono introdotte le definizioni della potenza reale, immaginaria e di sequenza zero e viene mostrato come questa teoria renda agevole la comprensione dei fenomeni causati da tensioni o correnti non sinusoidali. Essa è particolarmente adatta per il progetto di un caricabatteria quando esso viene visto come un condizionatore di potenza. Il capitolo sei è dedicato ai concetti di base dei filtri attivi di tipo shunt. Essi possono svolgere diversi tipi di funzioni, come la compensazione delle armoniche di corrente generate da carichi non lineari impedendo la loro propagazione nella rete. L’algoritmo di compensazione basato sulle potenze definite nel riferimento αβ è molto flessibile e quindi la teoria della potenza istantanea è stata considerata come la base per lo sviluppo del sistema di controllo dei filtri attivi. Alcuni esempi di compensazione descritti nel capitolo precedente sono stati simulati e sono stati riportati i risultati. Nel capitolo sette è considerato il dimensionamento dei dispositivi di potenza che costituiscono il caricabatteria in relazione ai diversi servizi ausiliari che esso può fornire. Sono stati dimensionati in tensione e corrente gli interruttori elettronici di potenza, gli induttori di accoppiamento con la rete e gli altri componenti passivi. Nel capitolo otto viene considerato un caricabatteria che alimenta il proprio carico e contemporaneamente compensa i carichi non lineari connessi nelle vicinanze, costituiti da raddrizzatori. Queste funzionalità aggiuntive in termini di condizionamento della potenza di rete sono state quantificate al fine di determinare la capacità di un caricabatteria costituito da determinati componenti attivi e passivi di supportare la rete svolgendo la funzione di filtro attivo. Nel nono capitolo sono state dimensionate le induttanze di filtro di un caricabatteria per uno specifico caso di studio in cui era richiesta la capacità sia di ricaricare la batteria che di iniettare potenza attiva in rete, sia nel caso di connessione monofase che trifase. La conoscenza dell’ampiezza dell’ondulazione di corrente è un requisito importante per il dimensionamento delle induttanze. Perciò è stato effettuato un calcolo preciso di questa grandezza sia nel caso di un caricabatteria connesso alla rete monofase e operante secondo la tecnica di PWM, sia nel caso di connessione alla rete trifase e adozione della tecnica SVM. Nel capitolo dieci viene considerato un caso di studio riguardo il dimensionamento di un filtro LCL. IL capitolo undici contiene uno studio teorico dei regolatori risonanti. Essi risolvono il problema posto dai convenzionali regolatori PI, che quando sono impiegati per il controllo di grandezze alternate, come accade nel caso delle correnti in un convertitore dc-ac, non sono in grado di annullare l’errore a regime a causa del guadagno finito alla frequenza di funzionamento. Un regolatore risonante presenta invece un guadagno idealmente infinito alla frequenza di funzionamento e quindi garantisce un errore a regime nullo. L’efficacia dei regolatori risonanti è stata verificata per mezzo di simulazioni. Nel capitolo dodici sono riportate le normative riguardanti i connettori, le modalità di ricarica e la connessione dei caricabatteria dei PEV alla rete elettrica. Esse mirano a definire una procedura di ricarica comune a tutti i PEV e tutte le infrastrutture di ricarica, siano esse pubbliche o private.

A set of algorithms building a program package for the generation of twoandthree-dimensional unstructured/hybrid grids around complex geometrieshas been developed. The unstructured part of the grid generator is based on the advancing frontalgorithm. Tetrahedra of variable size, as well as directionally stretched tetrahedracan be generated by specification of a proper background grid, initiallygenerated by a Delaunay algorithm. A marching layer prismatic grid generation algorithm has been developedfor the generation of grids for viscous flows. The algorithm is able to handleregions of narrow gaps, as well as concave regions. The body surface is describedby a triangular unstructured surface grid. The subsequent grid layers in theprismatic grid are marched away from the body by an algebraic procedurecombined with an optimization procedure, resulting in a semi-structured gridof prismatic cells. Adaptive computations using remeshing have been done with use of a gradientsensor. Several key-variables can be monitored simultaneously. The sensorindicates that only the key-variables with the largest gradients give a substantialcontribution to the sensor. The sensor gives directionally stretched grids. An algorithm for the surface definition of curved surfaces using a biharmonicequation has been developed. This representation of the surface canbe used both for projection of the new surface nodes in h-refinement, and theinitial generation of the surface grid. For unsteady flows an algorithm has been developed for the deformationof hybrid grids, based on the solution of the biharmonic equation for the deformationfield. The main advantage of the grid deformation algorithm is that itcan handle large deformations. It also produces a smooth deformation distributionfor cells which are very skewed or stretched. This is necessary in orderto handle the very thin cells in the prismatic layers. The algorithms have been applied to complex three-dimensional geometries,and the influence of the grid quality on the accuracy for a finite volumeflow solver has been studied for some simpler generic geometries.
QC 20100812

This thesis has been conducted in cooperation with the Norwegian transmission system operator, Statnett, and their research on two new interconnectors linking Norway to England and Germany. The work presented in this thesis has considered one of these interconnectors, with a third terminal connected offshore to allow for integration of offshore wind power and oil platforms, as shown in fig.~ref{fig:theGrid}.Investigation of the voltage source converters (VSCs) control ability as well as operational aspects of multi-terminal DC-grids has been performed. Identified as the key control variable of a DC-grid is the DC-voltage serving as a measure of power balance, since an unbalance will affect the DC-voltage through charging or discharging of the DC-capacitances. Utilizing VSCs allowing a fast and accurate control of the DC-voltage can lead to a stable operation of a DC-grid.The three-terminal structure, fig.~ref{fig:theGrid}, was implemented in the simulation tool SIMPOW and connected to a 35-node AC-grid model representing the Nordic grid. The simulation model was used for analyzes of the DC-grid operation and its affect on the connected AC-grids. The converter station connected to the Nordic grid were applied with DC-voltage control, implying that it will act as the power balancing unit of the DC-grid. The simulations performed show that the control structure implemented could assure a stable DC-grid operation within 0.3s of a fault. It identified the need for a fast response to changes in the DC-voltage as the influence of the other connected AC-grids were directly linked to DC-voltage oscillations. Simulations were also conducted to study the advantage of applying AC-voltage control compared to reactive power for the converter connected to the Nordic grid. It was identified that an increased stability of the Nordic grid could be assured during faults in the grid itself. This also affected the DC-grid operation through an increased capability of power exchange with the Nordic grid.

Darbo „Grid projektavimas“ tikslas – suprojektuoti, sukonfigūruoti telkinį Šiaulių universitete ir prijungti jį prie bendro Litgrid ir Balticgrid tinklyno. Pagrindiniai šio darbo uždaviniai yra orientuoti į darbo tikslą ir apima ne tik programinius sprendimus, bet ir vartotojų mokymų organizavimą bei galimybių šiam tikslui panaudoti mokymo klas÷se esančius kompiuterius analizę ir rekomendacijas. Šiame darbe įdiegta ir sukonfigūruota programin÷ įranga, telkinys prijungtas prie virtualiųjų organizacijų Litgrid ir Balticgrid, sukurti scenarijai, automatizuojantys programų diegimą ir konfigūravimą. Telkinio pristatymas, metodin÷s rekomendacijos ir mokymai darbui su juo buvo realizuoti dviejose konferencijose. Darbas inovatyvus tuo, kad tokio pobūdžio virtualus kompiuteris yra pirmasis ir vienintelis Šiaulių regione - jis sudaro sąlygas panaudoti jau turimus kompiuterius didel÷s apimties skaičiavimo resursams imlių uždavinių sprendimui.
The purpose of the project "Grid designing" is to design and to configure the cluster at Siauliai University and connect it to Litgrid and Balticgrid. The main problems of this project are orientated towards the objective of the project and include not only software solutions, but also organization of users training and analysis as well as recommendations on possibilities to employ computers located at the teaching classes for that purpose too. This project has installed and configured software, the cluster is connected to virtual organizations of Litgrid and Balticgrid, it has created scripts, which automates installation and configuration of programs. Cluster, methodological recommendations and training for it were presented in two conferences. The project is innovative because it is the first and the only virtual computer of such nature in Siauliai region, which enables to use available computers to solve tasks that require big volumes of calculating resources.

Textile Grid är ett undersökande textildesignprojektsom utforskar olika tekniker och material för atttänja på gränserna i textil. Utgångspunkten ärett enkelt rutmönster som översätts i teknikernatryck, väv och trikå. Rutmönstret fungerar som enkonstruktion i textilen och genom att jobba medkontrasterna mellan hårt och mjukt, samt rörelseoch stabilitet utforskas både textilens utseendeoch rörelse. Resultatet är fem material som viksoch formas efter sin egen konstruktion.

Textile Grid is a design projekt about exploring

different techniques and materials to expand the

boundaries of textile; what textile usually looks

like and how it appears. The starting-point is a

simple grid that is translated in screen-print,

knitting and weave. The grid works as a

construction in the textile. By playing with the

contrast between soft and hard, stability and

movement both the expression and the behavior

of the textile are explored.

Program: Textildesignutbildningen

The objective of the current study is development of a coupled orthogonal curvilinear/Cartesian grid solver. The solver requires a thin orthogonal boundary layer grid and a non-uniform Cartesian grid to resolve the boundary layer on a solid surface and the flow region away from the surface, respectively. Flows inside the orthogonal boundary layer and Cartesian background grids are solved by different CFD solvers which are coupled by an overset grid method. SUGGAR code writes the grid domain connectivity information into a file that identifies grid points necessary for the overset grid interpolation. In order to satisfy mass conservation across the overlapping region, the pressure Poisson equations and the overset interpolation equations are encompassed from both of the solvers and solved simultaneously by an iterative method.

Accuracy of the coupled orthogonal curvilinear/Cartesian grid solver was evaluated in terms of flows past circular cylinders because the orthogonal boundary layer grids can be generated easily due to its simple cylindrical shape. In this study, additional numerical simulations were also performed by the original orthogonal curvilinear and Cartesian grid solvers in order to obtain the benchmark data to compare with the results of the coupled orthogonal curvilinear/Cartesian grid solver.

The coupled orthogonal curvilinear/Cartesian grid solver was applied to steady and unsteady laminar flows at Re = 40 and 200, single-phase turbulent flows at subcritical Re = 3900 and supercritical Re = 5 × 10 ⁵ and 1 × 10⁶, and two-phase flows at (Re, Fr) = (2.7 × 10⁴, 0.20), (2.7 × 10⁴, 0.80), and (4.58 × 10⁵, 1.64). Those numerical results are in good agreement with the experimental and numerical results in the literature.

Effects of the grid resolution on the numerical results were analyzed in this study. The analysis showed the more accurate resolution of near-wall regions by the boundary layer grids for the coupled orthogonal curvilinear/Cartesian grid solver. It also presented the similar trends of the flow at the subcritical Re with the vertical resolution to those observed in the literature.

The coupled orthogonal curvilinear/Cartesian grid solver predicted much delayed separations of the boundary layers at both the supercritical Re, which caused the narrower wakes and the shorter recirculation regions than those at the subcritical Re. The features of surface pressure corresponded to the postponed separations.

The solver developed in this study showed the similar trends in the two-phase flows at Fr = 0.20 and 0.80 to those observed by the past numerical studies. The trends of the vortex shedding, deviating shear layers, and the expanded wake on the free surface are more prominent in the flow at Fr = 0.80 than that at Fr = 0.20. At Re = 4.58 × 10⁵ and Fr = 1.64, the flow near the free surface includes the small recirculation region behind the cylinder, which corresponds to the cavity structure on the free surface in the same region, and two large symmetric recirculation regions. The shear layers separating from the cylinder surface move along the outer edges of the recirculation regions. Another pair of the shear layers is separated from the smaller recirculation region.

With the rapid development of high-speed wide-area networks and powerful yet low-cost computational resources, grid computing has emerged as an attractive computing paradigm. The space limitations of conventional distributed systems can thus be overcome, to fully exploit the resources of under-utilised computing resources in every region around the world for distributed jobs. Workload and resource management are key grid services at the service level of grid software infrastructure, where issues of load balancing represent a common concern for most grid infrastructure developers. Although these are established research areas in parallel and distributed computing, grid computing environments present a number of new challenges, including large-scale computing resources, heterogeneous computing power, the autonomy of organisations hosting the resources, uneven job-arrival pattern among grid sites, considerable job transfer costs, and considerable communication overhead involved in capturing the load information of sites. This dissertation focuses on designing solutions for load balancing in computational grids that can cater for the unique characteristics of grid computing environments. To explore the solution space, we conducted a survey for load balancing solutions, which enabled discussion and comparison of existing approaches, and the delimiting and exploration of the apportion of solution space. A system model was developed to study the load-balancing problems in computational grid environments. In particular, we developed three decentralised algorithms for job dispatching and load balancing—using only partial information: the desirability-aware load balancing algorithm (DA), the performance-driven desirability-aware load-balancing algorithm (P-DA), and the performance-driven region-based load-balancing algorithm (P-RB). All three are scalable, dynamic, decentralised and sender-initiated. We conducted extensive simulation studies to analyse the performance of our load-balancing algorithms. Simulation results showed that the algorithms significantly outperform preexisting decentralised algorithms that are relevant to this research.

The installation of power generation systems based on renewable energy sources has been increasing exponentially over the last decades. However, in spite of the well-known merits of such energy sources, the expansion of renewable-based generation (RG) plants, which interface the grid through power converters, can produce also negative impacts on the electrical grid, due to its power processing mechanism, which is different from traditional generation plants. In fact, the regulation capability of the grid can decrease as much as the share of the RG increases. To avoid this, power conversion systems belonging to RG plants are requested to be more grid-friendly, and responsive to the electrical network conditions. In this way, they can contribute to the electrical network stability as other generation does, instead of behaving as simply grid-feeding systems focused on injecting as much power as possible.This PhD dissertation is focused on the control of grid-connected power converters with grid support functionalities based on the Synchronous Power Controller (SPC) concept. The SPC is an established solution for controlling grid connected power converters and equipping them with emulated and improved synchronous machine characteristics. In addition to the general goal of improving the grid interaction of the RG plants, grid support functionality stands as a main property among the characteristics given by the SPC. In this dissertation the virtual admittance structure, contained in the electrical block of the SPC, which emulates the stator output impedance of the synchronous machines, is analyzed. Moreover, it is extended to a study case where the admittance value can be different for positive- and negative-sequence components. The designed virtual admittance block contains three branches, which are responsible for positive-sequence current injection, negative-sequence current injection and other harmonic components, respectively. The converter¿s performance under asymmetrical grid fault is especially considered in this case.The analysis and arrangements in the design of the SPC¿s power loop controller is another contribution of this research. Other methods that consider synchronous machine emulation normally construct the controller by reproducing the synchronous generation swing equation. Based on the virtual implementation, which is free from mechanical constraints, one can set a proper damping factor achieving thus better dynamics compared to the traditional synchronous machines. However, the increase of the damping factor changes the inherent power-frequency (P-f) droop characteristics, which may lead to undesired deviations in the active power generation. In the framework of this PhD, a method that modifies the conventional swing equation emulation and lets the inherent P-f droop characteristics be configurable, independently of the inertia and damping characteristics, is proposed.The work presented in this dissertation is supported by mathematical and simulation analysis. Moreover, in order to endorse the conclusions achieved, a complete experimental validation has been conducted. As it will be shown, the performance of the SPC has been validated in tests once the main parts, namely virtual admittance and power loop controller, and other parts are settled. The simulation and experimental test scenarios include events like changes in the power operation point, frequency sweeps, voltage magnitude changes, start-up and parallel converters operation, which are given under different control configurations like the different structures for the power loop controller and different control parameters. This PhD research also compares the transient performance of the SPC-based power converters with the ones achieved with conventional control methods.
Los convertidores de potencia conectados a la red actúan comúnmente como interfaz entre plantas de generación basadas en energía renovable y la red eléctrica, permitiendo así el procesado de energía eólica y fotovoltaica y su inyección a red. El control de estos convertidores conectados a la red ha sido objeto de estudio en las últimas décadas, ya que su comportamiento y prestaciones influye de forma determinante tanto en la calidad de la red eléctrica, así como en el cumplimiento de los requisitos de conexión a la red fijados por los códigos de red. Junto con la expansión de las plantas de generación de energía renovable, su impacto en el sistema eléctrico ha crecido también, lo cual ha hecho que se lleven a cabo muchos trabajos de investigación orientados a armonizar la penetración de renovables con la estabilidad de la red. Con los sistemas de control actuales la capacidad de regulación de la red disminuye tanto como la proporción de la generación renovable aumenta. En las redes eléctricas del futuro, se espera que los convertidores de potencia, que actúan como interfaz, exploten sus posibilidades de cómputo y control permitiendo mejorar la interacción de la generación renovable con la red. En este contexto los controles de tipo “droop control”, los cuales son ampliamente utilizados en sistemas de generación tradicionales, se pueden aplicar a los convertidores conectados a red para habilitar funciones de soporte de red, ya que estos contribuyen al control de tensión y frecuencia primaria ajustando el intercambio de potencia activo y reactiva de forma proporcional a la desviación de la frecuencia y magnitud de la tensión en el punto de conexión. En el caso de regulación de frecuencia, y para que este sea bidireccional, el convertidor puede interactuar con la red con la ayuda de sistemas de almacenamiento de energía. Sin embargo, la inclusión del “droop control” no conlleva una solución global. Incluso si se ajusta de forma óptima y se dispone de reserva de energía, aún hay cuestiones como la respuesta inercial que no se pueden dar con este tipo de control. La generación en los sistemas tradicionales se lleva a cabo principalmente por generadores síncronos. Comparados con estos, los convertidores conectados a la red difieren principalmente en la falta de la característica electromecánica. En consecuencia, la estática y la dinámica de las unidades de generación de energía renovable son diferentes en comparación con los generadores síncronos. La dinámica de estos convertidores es altamente dependiente de los sistemas de sincronización (PLL), cuyo comportamiento se degrada en condiciones de red adversas o distorsionadas. Además, el control de potencia normalmente depende control de potencia instantáneo. Debido a las diferentes dinámicas, la inercia total en la red no aumenta junto con la integración de las energías renovables. Sin embargo, los códigos de red han incluido requerimientos tales como “inercia sintética" en los requisitos. Otras deficiencias del control del convertidor convencional incluyen el rendimiento inferior bajo condiciones de avería de red, en conexión de red débil y conexión de red de relación X / R baja. Esta tesis doctoral estudia y valida el control de los convertidores conectados a la red con funcionalidades de soporte de red. El objetivo general del trabajo es mejorar las características de interacción de la red de las plantas de generación de energía renovable mediante la especificación de los convertidores conectados a la red con características de la máquina síncrona emulada y mejorada. La tesis ha aportado contribuciones o ha mostrado originalidades en los siguientes aspectos: Un enfoque de ajuste de bucle de control de corriente interno generalizado; Diseño detallado y validación de la admisión virtual para convertidores conectados a la red; Diseño detallado y validación del circuito de control de potencia para la emulación de inercia y amortiguación.

Nordic Light are one off the leading companies in manufacturing and development of lamparmatures and have been doing that since 1980. Since LED lamps are getting more and more common, the demands on optimizing thearmatures are rising. Because of the competition in the lamp industry the customers put highdemands on the efficiency and price. The purpose of this paper is to optimize an existingarmature and the focus will be on efficiency and manufacturing costs. An analysis of the existing armature was made to establish the function and cost of everycomponent. This was the foundation for the ideation of the new armature. To ensure that thenew armature would manage the requirements, a calculations of manufacturing costs and ananalysis in OpticStudio was made. The result shows a solution more cost efficiant than the original with high efficiency where itis possible to attach the armature in the roof or to profiles. It is recommended to make aprototype and to perceive with additional calculations before the manufacturing starts.

Smart Grid (SG) is an electrical grid enhanced with information and communication technology capabilities, so it can support two-way electricity and communication flows among various entities in the grid. The aim of SG is to make the electricity industry operate more efficiently and to provide electricity in a more secure, reliable and sustainable manner. Automated Meter Reading (AMR) and Smart Electric Vehicle (SEV) charging are two SG applications tipped to play a major role in achieving this aim. The AMR application allows different SG entities to collect users’ fine-grained metering data measured by users’ Smart Meters (SMs). The SEV charging application allows EVs’ charging parameters to be changed depending on the grid’s state in return for incentives for the EV owners. However, both applications impose risks on users’ privacy. Entities having access to users’ fine-grained metering data may use such data to infer individual users’ personal habits. In addition, users’ private information such as users’/EVs’ identities and charging locations could be exposed when EVs are charged. Entities may use such information to learn users’ whereabouts, thus breach their privacy. This thesis proposes secure and user privacy-preserving protocols to support AMR and SEV charging in an efficient, scalable and cost-effective manner. First, it investigates both applications. For AMR, (1) it specifies an extensive set of functional requirements taking into account the way liberalised electricity markets work and the interests of all SG entities, (2) it performs a comprehensive threat analysis, based on which, (3) it specifies security and privacy requirements, and (4) it proposes to divide users’ data into two types: operational data (used for grid management) and accountable data (used for billing). For SEV charging, (1) it specifies two modes of charging: price-driven mode and price-control-driven mode, and (2) it analyses two use-cases: price-driven roaming SEV charging at home location and price-control-driven roaming SEV charging at home location, by performing threat analysis and specifying sets of functional, security and privacy requirements for each of the two cases. Second, it proposes a novel Decentralized, Efficient, Privacy-preserving and Selective Aggregation (DEP2SA) protocol to allow SG entities to collect users’ fine-grained operational metering data while preserving users’ privacy. DEP2SA uses the homomorphic Paillier cryptosystem to ensure the confidentiality of the metering data during their transit and data aggregation process. To preserve users’ privacy with minimum performance penalty, users’ metering data are classified and aggregated accordingly by their respective local gateways based on the users’ locations and their contracted suppliers. In this way, authorised SG entities can only receive the aggregated data of users they have contracts with. DEP2SA has been analysed in terms of security, computational and communication overheads, and the results show that it is more secure, efficient and scalable as compared with related work. Third, it proposes a novel suite of five protocols to allow (1) suppliers to collect users accountable metering data, and (2) users (i) to access, manage and control their own metering data and (ii) to switch between electricity tariffs and suppliers, in an efficient and scalable manner. The main ideas are: (i) each SM to have a register, named accounting register, dedicated only for storing the user’s accountable data, (ii) this register is updated by design at a low frequency, (iii) the user’s supplier has unlimited access to this register, and (iv) the user cancustomise how often this register is updated with new data. The suite has been analysed in terms of security, computational and communication overheads. Fourth, it proposes a novel protocol, known as Roaming Electric Vehicle Charging and Billing, an Anonymous Multi-User (REVCBAMU) protocol, to support the priced-driven roaming SEV charging at home location. During a charging session, a roaming EV user uses a pseudonym of the EV (known only to the user’s contracted supplier) which is anonymously signed by the user’s private key. This protocol protects the user’s identity privacy from other suppliers as well as the user’s privacy of location from its own supplier. Further, it allows the user’s contracted supplier to authenticate the EV and the user. Using two-factor authentication approach a multi-user EV charging is supported and different legitimate EV users (e.g., family members) can be held accountable for their charging sessions. With each charging session, the EV uses a different pseudonym which prevents adversaries from linking the different charging sessions of the same EV. On an application level, REVCBAMU supports fair user billing, i.e., each user pays only for his/her own energy consumption, and an open EV marketplace in which EV users can safely choose among different remote host suppliers. The protocol has been analysed in terms of security and computational overheads.

This thesis evaluates software engineering methods, especially event modelling of distributed systems architecture, by applying them to specific data-grid projects. Other methods evaluated include requirements' analysis, formal architectural definition and discrete event simulation. A novel technique for matching architectural styles to requirements is introduced. Data-grids are a new class of networked information systems arising from e-science, itself an emergent method for computer-based collaborative research in the physical sciences. The tools used in general grid systems, which federate distributed resources, are reviewed, showing that they do not clearly guide architecture. The data-grid projects, which join heterogeneous data stores specifically, put required qualities at risk. Such risk of failure is mitigated in the EGSO and AstroGrid solar physics data-grid projects' designs by modelling. Design errors are trapped by rapidly encoding and evaluating informal concepts, architecture, component interaction and objects. The success of software engineering modelling techniques depends on the models' accuracy, ability to demonstrate the required properties, and clarity (so project managers and developers can act on findings). The novel formal event modelling language chosen, FSP, meets these criteria at the diverse early lifecycle stages (unlike some techniques trialled). Models permit very early testing, finding hidden complexity, gaps in designed protocols and risks of unreliability. However, simulation is shown to be more suitable for evaluating qualities like scalability, which emerge when there are many component instances. Design patterns (which may be reused in other data-grids to resolve commonly encountered challenges) are exposed in these models. A method for generating useful models rapidly, introducing the strength of iterative lifecycles to sequential projects, also arises. Despite reported resistance to innovation in industry, the software engineering techniques demonstrated may benefit commercial information systems too.

Smart grid technologies are starting to be the future of electric power systems. These systems are giving the utilities detailed information about their systems in real time. One of the most challenging things of implementing smart grid applications is employing the communications into the systems. Understanding the available communications can help ease the transition to these smart grid applications. Many of the utility personnel are spending too much time trying to figure out which communication is better for their application or applications. So this thesis presents the different communication types available with discussing the different attributes in which these communication types are going to offer to the utility. Then these communication types are looked such that utilities can quickly understand how to approach the difficult task of obtaining the information from the different smart grid applications by the use of different communication options.

Thesis (M. Arch.)--Massachusetts Institute of Technology, Dept. of Architecture, 2007.
Includes bibliographical references (p. 87-90).
The American landscape chronicles the dreams of an agricultural nation through a series of regular lines en-scribed on a flat plane. Each 6 mile x 6 mile square frames a lose-lose situation in which government subsidies encourage intensive monocultural production resulting in loss of topsoil, biodiversity and population while contaminating the ground with chemicals and glutting global commodity markets. Current "advances" in agricultural research demonstrate that age-old technologies - small scale rotational systems - properly managed, can multiply productivity while rehabilitating soils, retaining moisture and reducing or eliminating chemical applications. At a fragile moment in history when only 2% of the population produces the agriculture which supports the other 98%, this thesis proposes an alternative to the current agro-political landscape in which rational lines no longer suffice to measure a rotational landscape.
Ophelia Wilkins.
M.Arch.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Architecture, 2011.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 99-101).
The grid in architecture is a systematic organization of space. The means that architects use to organize space are, almost by definition, rigid and totalizing. The Cartesian grid, which will serve as the antagonist of the soft grid, is geometrically and topologically unyielding on both the local and global scales. There are, however, alternatives to such hard grids. Through a series of studies, this thesis will catalog and analyze the soft girds, i.e. those that are adaptive, variable, scalable, asymmetrical and entropic. Computational tools in architecture have, in recent years, enabled designers to manage geometries that until now have been realizable only by analog means. The instrumental capacity for complex designs has lead to increased demand for soft gridding systems as is evidenced by the profusion of Voronoi diagrams, pixelations, distorted grids and Danzer tilings in student and conceptual work. However, the built scale of such projects is rarely beyond installation largely because of the difficulty in managing spatial organizations that are not essentially Cartesian. Th is thesis will lay the groundwork for a systematic understanding of the possibilities of soft grids while providing much of the computational tools to generate and manage specific examples.
by Ari Kardasis.
S.M.

Ruins have always fascinated me. These eerie, abandoned, man made buildings, hold you in awe. Buildings no longer in use, tell their story through whatever remains. What does one do with the ruins? Preserve, destroy or reinterpret? How do you build with ruins? How much do you destroy? How much do you retain? How do you build anew? One such ruin is that of Mc Millan Sand Filtration Plant in Washington DC. A completely utilitarian structure, with a huge grid of columns covered with a roof spread over 25 acres of land. What appears from the eye level as a 25 acre lawn with a grid of manholes, interspersed with two rows of gigantic concrete towers, is actually a water purification plant that used a slow sand fi ltration process (purifying water by passing it through sand and gravel) to supply potable drinking water. The grids (of columns and manholes) are the most striking features. When the manhole covers are opened, they cast a pattern of light on the fl oor. The manhole grid itself can be interpreted as a grid of skylights. Furthermore, there are various extents of deterioration this purification plant has undergone, due to which the grids are presented in a variety of ways: As a grid of columns with the roof of manholes (structure intact); As a grid of columns without the roof (columns not strong enough to hold the roof); As a collapsed structure/ mass of earth (complete state of deterioration). Though water was the essence, the very reason why this plant was in existence, today this piece of land lies parched and thirsty. Much was happening on this seemingly calm piece of land. I wanted to bring out its essence, reveal its grids, the unending array of columns, the play of light and shade they caused and most importantly, I wanted to bring water back to where it belonged. This thesis also explores the possibility of building on/with the â oldâ in a strong existing context by introducing a shift/rotation in the grid and with the help of material and texture.
Master of Architecture

Variable renewable energy sources are today increasingly integrated in the power system as a step towards the renewable society. The large-scale introduction of converter-based energy sources brings challenges in terms of reduced damping to the power system due to the reduced number of synchronous generators. This can be manifested as high rate-of-change-of-frequency and decreased grid stability. To forestall this reduced performance, it is suggested that the grid-following control of today’s converters are restructured to a grid-forming control, enabling the converter to behave closer to a synchronous machine.   This thesis compares grid-following and grid-forming control and seeks to further describe this grid-forming behavior by applying a grid-forming control method on an energy storage enhanced STATCOM-system. A continuous time model and a linearized model based on state space representations are constructed in order to investigate the grid-forming behavior but also how the converter stability is affected by a restructure from grid-following to grid-forming control.   The results indicate that the investigated grid-forming control method displays a behavior similar to synchronous machines and incorporates the ability to provide frequency response services and so called “synthetic inertia” to the grid.  The results also show that the stability of the converter (the ability to provide a bounded output when the system is perturbed) is ensured when the control method is restructured from grid-following to grid-forming and that the investigated grid-forming method is stable also in weak grid situations.

Målet med den här undersökningen har varit att se om fastigheten Orkestern 1 går att koppla off-grid och om det är ekonomiskt försvarbart eller om en on-grid lösning är bättre. Förutsättningarna är goda med ett stort tak med plats för solpaneler i öst-västlig riktning och en årsmedelvind på 4 m/s. Då huset är nybyggt och välisolerat är även energiförbrukning låg. För att kunna beräkna hur mycket energi som ska produceras i form av värme och el med hjälp av solceller, vindkraftverk, pelletskamin och dieselverk upprättas en energibalans och energifördelning med hjälp av transmission och ventilationsberäkningar. Lagring av energi görs i form av pellets, batteri och biodiesel. Simuleringsprogrammet för solceller Polysun används för att beräkna produktion av solel över varje månad på året. Diagram upprättas över året indelat i månader där det framgår hur stort energibehovet är och visar hur stor del varje energiproducent har varje månad. En pay-off kalkyl görs för att se om det är ekonomiskt lönsamt och för att kunna jämföra mellan två olika off-grid system. Pay-off kalkylen används också för att jämföra mellan off-grid och on-grid system. Resultatet landar i att on-grid systemet är ekonomiskt hållbart medan off-grid systemet inte är det men är ändå fullt genomförbart.
The main target of this examination has been to see if the real estate Orkestern 1 has the possibility to go off-grid and if it is economical defendable or if on-grid solution is a better way to go. The prerequisites are good with a large roof to place solar panels to the east and west, a yearly average windspeed at 4 m/s and a low energy consumption because the house is new built and well insulated. To calculate how much energy that must be produced in form of heat and electricity with solar cells, windmills, pellet stove and diesel generator an energy balance and an energy distribution will be prepared with help of calculations of transmission and ventilation loses. Storage of energy will be done in form of pellets, battery and biodiesel. The simulation program for solar panels Polysun is used to calculate the produced solar energy for each month on the year. Diagram is prepared for each month to see the need of energy and how much every energy producer is delivering. A straight pay-off calculation is done to see if there are any economic benefits and to compare between off-grid and on-grid systems. The result will be that on-grid system is better economical but still the off-grid system is doable.

An increased need for collaborative research among different organizations, together with continuing advances in communication technology and computer hardware, has facilitated the development of distributed systems that can provide users non-trivial access to geographically dispersed computing resources (processors, storage, applications, data, instruments, etc.) that are administered in multiple computer domains. The term grid computing or grids is popularly used to refer to such distributed systems. A broader definition of grid computing includes the use of computing resources within an organization for running organization-specific applications. This research is in the context of using grid computing within an enterprise to maximize the use of available hardware and software resources for processing enterprise applications. Large scale scientific simulations have traditionally been the primary benefactor of grid computing. The application of this technology to simulation in industry has, however, been negligible. This research investigates how grid technology can be effectively exploited by simulation practitioners using Windows-based commercially available simulation packages to model simulations in industry. These packages are commonly referred to as Commercial Off-The-Shelf (COTS) Simulation Packages (CSPs). The study identifies several higher level grid services that could be potentially used to support the practise of simulation in industry. It proposes a grid computing framework to investigate these services in the context of CSP-based simulations. This framework is called the CSP-Grid Computing (CSP-GC) Framework. Each identified higher level grid service in this framework is referred to as a CSP-specific service. A total of six case studies are presented to experimentally evaluate how grid computing technologies can be used together with unmodified simulation packages to support some of the CSP-specific services. The contribution of this thesis is the CSP-GC framework that identifies how simulation practise in industry may benefit from the use of grid technology. A further contribution is the recognition of specific grid computing software (grid middleware) that can possibly be used together with existing CSPs to provide grid support. With its focus on end-users and end-user tools, it is intended that this research will encourage wider adoption of grid computing in the workplace and that simulation users will derive benefit from using this technology.

This thesis investigates the dynamic behaviour and transients of a sub-system when operating in two scenarios: Grid-connected mode, and islanding mode. The sub-system consists of two distributed generators (DGs). One DG is modeled using a rotating synchronous machine fitted with a governor to represent a diesel generator, while the other is modeled using a DC voltage source and a converter to represent a photovoltaic (PV) energy source. The distribution network also consists of a grid connected source known as the main grid. During normal operation, the supply of electricity to the connected loads is shared among the three energy sources, the DGs supplying about 80 percent of the loads and the rest are supplied by the main grid. When the main grid is disconnected from the network, supply to the connected loads is shared by the two DGs. The PV energy source system is equipped with real and reactive power control mechanisms that minimize islanding transients and maintain angle stability and voltage quality of the network. The study includes examples of micro-grid transient analysis carried out in the past. This is followed by the study of how transient analysis can be carried out in PowerFactory software. The simulation studies show that the electronic power control system in a PV generator is capable of maintaining the angle stability of a micro grid in response to transient conditions. These transients may result from changes in power demands from connected loads or severe islanding events. The diesel generator through the use of a governor responds to supply the required power to the system when the PV has reached its maximum supply limits. The diesel generator acts as a back-up to the PV supply.

The global energy production from renewable sources is increasing, with high penetration of both wind and solar in key regions. Ocean Wave Energy is projected to contribute with an increasing share of the future power supply, and the focus of this work is to investigate the requirements for connecting wave energy to the power grid, in context of the Fred. Olsen (FO) Wave Energy Project. Most Wave Energy Converters (WECs) produce highly distorted power due to the reciprocal motion induced by the ocean waves. Some WEC systems have integrated energy storage that overcomes this limitation, but adds significant expenses. As an alternative approach, this work investigates direct power export that relies on aggregate smoothing among several WECs. By optimizing the position of the WEC devices with respect to the incoming waves, fluctuations may be mutually canceled out between the devices. FO has closely monitored the global development within wave energy for about two decades, and has worked actively on developing WECs since 2002. The latest WEC system, named Lifesaver, has been in operation since April 2012 and is the basis of this thesis work. The Lifesaver system is described in detail, and comprehensive data on operational performance is presented. The major cost driver for grid integration is the peak to average power ratio, which can be as high as 20 in the early power conversion stages. Thus, it is crucial to improve the power quality early in the conversion chain so that the downstream power system is efficiently utilized. The simulations undertaken in this work indicate that a high quality power output can be achieved at the farm level, but that significant oversize factors will be required in the intermediate power systems within the farm. Cost-benefit analysis of the system show that a grid connected system at the current technology level will return marginal profitability. Therefore, several alternative approaches are investigated that could serve as a bridge towards future large scale systems. This includes autonomous systems that could supply power to remote ocean based units such as measurement and surveillance buoys, aquaculture facilities and support systems for the off-shore oil and gas industry. In general, the findings show that the WEC system is well suited for grid integration, although it becomes clear that significant development remains before wave energy can become an important supplement in the energy mix. Moreover, there seems to be a market for autonomous systems that is economically viable at the current technology level that could allow for immediate deployment of commercial systems.

This thesis proposes an approach for the design and implementation of collaborative cache systems in grids that supports capabilities for monitoring and controlling cache interactions. Our approach permits to compose and evaluate high-level collaborative cache functions in a flexible way. Our proposal is based on a multilayer model that defines the main functions of a collaborative grid cache system. This model and the provided specification are used to build a flexible and generic software infrastructure for the operation and control of collaborative caches. This infrastructure is composed of a group of autonomous cache elements called Grid Cache Services (GCS). The GCS is a local administrator of temporary storage and data which is implemented as a grid service that provides the cache capabilities defined by the model. We study a possible configuration for a group of GCS that constitutes a basic management system of temporary data called Temporal Storage Service (TSS)
Cette thèse propose une approche de la conception et de l'implémentation de systèmes de cache collaboratif dans les grilles de données. Notre approche permet la composition et l'évaluation des fonctions d‘un système de cache collaboratif de haut niveau de façon flexible. Notre proposition est basée sur un modèle multicouche qui définit les fonctions principales d'un système de cache collaboratif pour les grilles. Ce modèle et la spécification fournie sont utilisés pour construire une infrastructure logicielle flexible et générique pour l'opération et le contrôle du cache collaboratif. Cette infrastructure est composée d'un groupe d’éléments autonomes de cache appelés "Grid Cache Services" (GCS). Le GCS est un administrateur local de moyens de stockage et de données temporaires. Nous étudions une possible configuration d’un groupe de GCS qui constitue un système basique d'administration de données temporaires appelé "Temporal Storage Service" (TSS)

Thesis (Ph. D.)--University of California, San Diego, 2006.
Title from first page of PDF file (viewed December 13, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 110-115).

1 Einleitung 1.1 Motivation 1.2 Aufgabenstellung 1.3 Aufbau der Arbeit 2 Fachliches Umfeld 2.1 Grid Computing 2.2 Idle Time Computing 3 Ressourcenpartitionierung 3.1 Ressourcenpartitionierung und Scheduling 3.2 Ressourcenpartitionierung in Idle Time Computing 3.2.1 Administrative Kontrolle der Ressourcen 3.2.2 Mindestgarantien zur Sicherstellung der Lauffähigkeit 3.3 Vorhandene Lösungen und verwandte Arbeiten 3.3.3 Ressourcenmanagement im Globus Toolkit 3.3.4 Ressourcenmanagement in Condor 3.3.5 Das GARA Framework 3.3.6 Distributed Resource Management Application API 3.3.7 Grid Resource Allocation Agreement Protocol 3.3.8 SNAP 3.3.9 OGSI-Agreement 3.3.10 PBS/Maui und andere Batch Systeme 3.3.11 Wide Area Distributed Computing 3.3.12 Weitere verwandte Arbeiten 3.3.13 Überlegungen zum Ressourcenbedarf 4 Ressourcenkontrolle in Desktopbetriebssystemen 4.1 Ressourcen 4.2 Ressourcenpartitionierung unter Linux 4.2.14 Festplattenkapazität 4.2.15 Arbeitsspeicher 4.2.16 Netzwerkbandbreite 4.2.17 CPU Kapazität 4.3 Ressourcenpartitionierung unter Microsoft Windows XP 4.3.18 Festplattenkapazität 4.3.19 Arbeitsspeicher 4.3.20 Netzwerkbandbreite 4.3.21 CPU Kapazität 4.4 Fazit 5 Entwurf und Design des Frameworks 5.1 Entwurfsgrundlage - Komponentenarchitektur 5.2 Architektur 5.2.22 Broker Server 5.2.23 Broker Software auf den Clients 5.2.24 Schnittstellen 5.3 Komponententypmodell 5.4 Ressourcenidentifikation und Ressourcenzuordnung 5.5 Anbindung ans Grid 5.6 Datenbankentwurf 5.7 XML RPC Schnittstelle 6 Implementierung 6.1 Broker Server 6.1.25 Datenbank 6.1.26 Komponenten 6.1.27 Webserverskripte 6.1.28 Database Crawler 6.2 Komponenten 6.2.29 Network 6.2.30 DSCP 6.2.31 Quota 6.2.32 FSF 6.3 Linux Client 6.3.33 Broker Client 6.3.34 Komponenten 6.4 Windows Client 6.5 Abhängigkeiten 7 Evaluierung 7.1 Durchgeführte Test- und Anwendungsfälle 7.1.35 Test der Clientsoftware 7.1.36 Test der Serversoftware 7.1.37 Durchführbare Anwendungsfälle 7.2 Evaluierung der Frameworkimplementierung 7.2.38 Performanz der Serverimplementierung 7.2.39 Zuverlässigkeit der Partitionierungen 7.3 Evaluierung von Traffic Shaping mit iproute2 7.3.40 Szenario 1 7.3.41 Szenario 2 7.3.42 Szenario 3 7.3.43 Fazit 8 Zusammenfassung und Ausblick 8.1 Fazit 8.2 Weiterentwicklung 8.2.44 Weiterentwicklungen auf Entwurfsebene 8.2.45 Weiterentwicklungen auf Implementierungsebene Anhang A: Details zum Datenbankentwurf Anhang B: Bildschirmfotos der Weboberfläche Anhang C: Quellcode Linux Broker Client Anhang D: Inhalt des beiliegenden Datenträgers

Tiek atskiro žmogaus, tiek ir šalies gyvenime saugumas – pamatinė vertybė, kuri yra neatsiejama bei labai svarbi ir šių dienų informacinių technologijų pasaulyje. Todėl, natūralu, kad informacijos saugumas tampa vis aktualesne problema. Organizacijose vykstančių procesų saugumui užtikrinti kuriami įvairūs saugumo įrankiai, kurie turi užtikrinti vartotojų ar paslaugų identiškumą (autentifikaciją), apsaugoti bendravimo vientisumą, privatumą, apibrėžti kam yra leidžiama kokius veiksmus vykdyti ir informacijos išteklius naudoti (autorizacija) ir kita. GRID sistemos suteikia galimybę naudotis WS (interneto paslaugų) pagrindu ir ne WS pagrindu paremta autentifikacija ir autorizacija GSI (GRID saugumo infrastuktūrai) užtikrinti. Abu metodai yra pagrįsti tokia pačia baze, t.y. paremti X.509 galinės esybės ir proxy sertifikatų standartu, kuris yra naudojamas identifikuojant pastovias esybes, tokias kaip vartotojai ir paslaugos, be to, leidžia priskirti laikinas privilegijas kitoms esybėms. Darbo tikslas – ištirti sertifikatų sistemą, šios sitemos komponentus, kurie yra diegiami į GRID sistemas bei pasiūlyti savo metodus ar modelius, kaip būtų galima pašalinti esamų sistemų saugumo trūkumus. Uždaviniai: 1. Išanalizuoti GRID saugumo infrastruktūros elementus ir suformuluoti egzistuojančias saugumo problemas. 2. Išanalizuoti suformuluotų problemų sprendimo būdus. 3. Remiantis problemų sprendimo būdais, suprojektuoti sertifikatų centro modelį ir proxy sertifikatų valdymo mechanizmą. 4... [toliau žr. visą tekstą]
Both in the persons and in the country's life security - the underlying value, which in these days is an integral and very important in information technology world. It is therefore natural that information security is becoming increasingly urgent problem. To ensure the safety of organizations processes the various security tools are being developed. They should ensure the identity of users or services (authentication), to protect communication integrity, privacy, to define who is allowed to carry out all activities and information resources to use (authorization) and the other. GRID system provides ability to use the WAS (Web Services) and non-WS based authentication and authorization to ensure the GSI (GRID Security infrastructure). Both methods are based on the same basis - X.509 end entity certificates and proxy certificates standard, which is used to identify end entities such as users and services, in addition, allows to assign privileges to other temporary end entities. The aim of the work – investigate a system of certificates, components of these system, which is introduced into GRID systems and to offer the methods or models how to eliminate security weaknesses in existing systems. The tasks: 1. To analyze the GRID security infrastructure elements and to formulate the existing safety problems. 2. To analyze formulated problem-solving techniques. 3. On the basis of problem-solving techniques to design certificate center model and proxy certificates management... [to full text]

High-voltage direct current (HVDC) has been proven an affordable and technically capable solution to bring vast amounts of power over long distances, though overhead lines, underground or undersea cables. As a result, a large number of point-to-point HVDC links appeared in several locations over the last decades. The technological step currently going on is the connection of point-to-point links to form a multi-terminal dc (MTDC) grid, a configuration that would bring several advantages. The construction of MTDC grids faces a few technical challenges, where the most notorious one might be dc grid protection. This thesis presents protection strategies for MTDC grids equipped with different dc fault clearance and isolation devices. These include ac circuit breakers (ACCBs), converters with fault blocking (FB) capability, dc circuit breakers (DCCBs) and fast dc disconnectors (only for isolation purposes). Each of these strategies in presented in a chapter, where the steps of the protection strategy are described and overvoltage suppression methods are proposed. The protection strategies include dc fault detection and dc fault discrimination algorithms. In literature, extensive research is available regarding dc fault discrimination, potentially the "hottest" topic in dc protection. In this thesis, discrimination algorithms are proposed being those based on analysis of local currents and voltages. Thus, link communication channels are not required, which reduces the overall decision-making time. The performance of the developed protection strategies is tested in PSCAD/EMTDC environment. DC faults are applied on two MTDC grids, including a 4-terminal meshed grid and the CIGRE 11-terminal dc grid. The main outcomes of this thesis include the discriminative fault criteria and the tailored protection strategies for dc grids equipped with either ACCBs, FB converters or DCCBs as main fault current clearance devices.

The ultimate goal of this study is to develop a 'tool' by which large-scale unstructured grids for realistic engineering problems can be generated efficiently on any parallel computer platform. The adopted strategy is based upon a geometrical partitioning concept, where the computational domain is sub-divided into a number of sub-domains which are then gridded independently in parallel. This study focuses on three-dimensional applications only, and it implements a Delaunay triangulation based generator to generate the sub-domain grids. Two different approaches have been investigated, where the variations between them are limited to (i) the domain decomposition and (ii) the inter-domain boundary gridding algorithms only. In order to carry out the domain decomposition task, the first approach requires an initial tetrahedral grid to be constructed, whilst the second approach operates directly on the boundary triangular grid. Hence, this thesis will refer to the first approach as 'indirect decomposition method' and to the second as 'direct decomposition method'. Work presented in this thesis also concerns the development of a framework in which all different sub-algorithms are integrated in combination with a specially designed parallel processing technique, termed as Dynamic Parallel Processing (DPP). The framework adopts the Message Passing Library (MPL) programming model and implements a Single Program Multiple Data (SPMD) structure with a Manager/Workers mechanism. The DPP provides great flexibility and efficiency in exploiting the available computing resources. The framework has proved to be a very effective tool for generating large-scale grids. Grids of realistic engineering problems and to the order of 115 million elements, generated using one processor on an SGI Challenge machine with 512 MBytes of shared memory, will be presented.

This thesis aims at facilitating the design and deployment of distributed applications on Grids, using a component-based programming approach. The specific issues in Grid computing addressed by the proposal of this thesis are: complexity of design, deployment, flexibility and high performance. We propose and justify a component model and an implementation framework. Our component model grounds on the Fractal component model and the active object model, It takes advantage of, first, the hierarchical model, well defined semantics and extensibility of the Fractal model, and second, the identification of components as configurable activities. We define a deployment model based on the concept of virtual architectures, and we propose primitives for collective communications through the specification of collective interfaces. Collective interfaces handle data distribution, parallelism and synchronization of invocations. They establish a basis for defining complex interactions between multiple components. We realized an implementation of this model on top of the ProActive Grid middleware, therefore benefiting from underlying features of ProActive. We demonstrate the scalability and efficiency of the framework by developing and deploying on several hundred nodes a compute and communication-intensive application, and we take advantage of the collective interfaces to develop a component-based SPMD application with benchmarks
L’objectif de cette thèse est de faciliter la conception et le déploiement d’applications distribuées sur la Grille, en utilisant une approche orientée composants. Les problématiques du calcul sur grilles abordées dans notre proposition sont: la complexité de conception, le déploiement, la flexibilité et la performance. Nous proposons et justifions un modèle de composants et son implantation. Le modèle proposé repose sur le modèle de composants Fractal et sur le modèle des objets actifs. Il bénéficie d’une part, de la structure hiérarchique et de la définition précise du modèle Fractal, et d’autre part, de l’identification des composants comme activités configurables. Nous proposons un modèle de déploiement et nous spécifions un ensemble de primitives pour les communications collectives, grâce à la définition d’interfaces collectives. Les interfaces collectives permettent de gérer la distribution des données, le parallélisme et la synchronisation des invocations. Nous avons développé une implantation du modèle proposé avec l’intergiciel de grille ProActive. Le framework de composants bénéficie ainsi des fonctionnalités sous-jacentes offertes par l’intergiciel ProActive. Nous démontrons la capacité de passage à l’échelle et l’efficacité de notre framework en déployant sur plusieurs centaines de machines des applications intensives en termes de calcul et de communications. Nous mettons à profit les interfaces collectives pour développer une application SPMD à base de composants, dont nous évaluons les performances

From the ancient times, people used various kinds of natural material to build architecture. Because of the characteristics of natural materials, there are many limits to challenge the possibility of the architectural structure.After the fire of 1871 in Chicago, there were many incentives to convince Chicago architects to use steel as the material in grid structure buildings. For example, rising real estate prices, the advent of the safety elevator and availability of cost effective steel members. After that, grid structures play a very important role in modern architectural history. Now, construction technologies are improving and hundreds of structure types can be used. Architects have more power to build various kinds of amazing space. For instance, TWA terminal of J.F.K. International Airport. However, the grid structure still has several advantages that can not be substituted: (1) It costs less money due to repetition of components across similar bays. (2) It reduces the construction time, and (3) It possesses an inherent order, a good prerequisite for plan and section. In addition, new technology extends the span limits of grid structures. Thus, grid structures have more chances to take on different roles in the definition of space. This project is a study of the relations between structural grid and architectural space, and a search for several distinct spaces within the grid. In other words, the concept of the project is setting up a grid structure, then developing spacial ideas according to program. So, we can reserve the spirit of the grid structure, and it offers many chances to us to think about other roles that the grid structure can play.
Master of Architecture

Thesis (Ph. D.)--West Virginia University, 1999.
Title from document title page. Document formatted into pages; contains vii, 69 p. : ill. Includes abstract. Includes bibliographical references (p. 67-69).

Texas Instruments has been developing Power Line Communication (PLC) technology to provide a form of communication for worldwide applications. By utilizing power grids within an infrastructure, it is possible to transmit a signal through the existing power lines such as a network would. Transmission of data within the electrical grid proves to be inherently noisy, thus compromising any information that is sent over the network. In order to provide a reliable platform of communication, frequency and impedance variation needs to be analyzed in order to provide proper development into PLC solutions. Within the scope of this project an analytical tool was developed to provide engineers with a method to determine impedance and frequency variations. Analysis and testing has been conducted to ensure the device satisfies the design requirements.

The goal of the present work is the development of a numerical method for compressible viscous flows on mixed unstructured grids. The discretisation is based on a vertex-centred finite-volume method. The concept of grid transparency is developed as a framework for the discretisation on mixed unstructured grids. A grid-transparent method does not require information on the cell types. For this reason, the numerical method developed in the present work can be applied to triangular, quadrilateral, and mixed grids without modification. The inviscid fluxes are discretised using the approximate Riemann solver of Roe. A limited linear-reconstruction method leads to monotonic capturing of shock waves and second-order accuracy in smooth regions of the flow. The discretisation of the viscous fluxes on triangular and quadrilateral grids is first studied by reference to Laplace's equation. A variety of schemes are evaluated against several criteria. The chosen discretisation is then extended to the viscous fluxes in the Navier-Stokes equations. A careful study of the various terms allows a form to be developed which may be regarded as a thin-shear-layer approximation. In contrast to previous implementations, however, the present approximation does not require knowledge of normal and tangential coordinate directions near solid surfaces. The effects of turbulence are modelled through the eddy-viscosity hypothesis and the one-equation model of Spalart and Allmaras. The discrete equations are marched to the steady-state solution by an explicit Runge-Kutta method with local time-stepping. The turbulence-model equation is solved by a point-implicit method. To accelerate the convergence rate, an agglomeration multigrid method is employed. In contrast to previous implementations, the governing equations are entirely rediscretised on the coarse grid levels. The solution method is applied to various inviscid, laminar, and turbulent flows. The performance of the multigrid method is compared for triangular and quadrilateral grids. Care is taken to assess numerical errors through grid-refinement studies or comparisons with analytical solutions or experimental data. The main contributions of the present work are the careful development of a solution method for compressible viscous flows on mixed unstructured grids and the comparison of the impact of triangular, quadrilateral, and mixed grids on convergence rates and solution quality.

Ces travaux portent sur la commande d’un micro-réseau interactif pour fournir des services système à un réseau électrique faible, et plus particulièrement une réponse primaire en fréquence et en tension au point d’interconnection (PCC). Le premier objectif de cette thèse est de superviser un micro-réseau afin d’assurer un fonctionnement stable tout en respectant les objectifs économiques définis par un optimiseur externe.Dans un second temps, une nouvelle méthodologie en trois étapes a été mise au point. Premièrement, pour fournir les services auxiliaires au PCC, il est nécessaire d’estimer et de coordonner les flexibilités des différents équipements tels que les générateurs d’énergie distribués, les énergies renouvelables, les stockages, etc. Un algorithme d’optimisation est proposé pour l’agrégation de ces flexibilités afin de déterminer les flux de puissance active et réactive maximum que le micro-réseau peut fournir. La deuxième étape détermine le comportement possible du micro-réseau à son PCC. Enfin, deux nouveaux algorithmes de contrôle ont été développés pour assurer un comportement de type statisme au PCC.Une première solution, basée sur un superviseur centralisé et la commande prédictive, assure un ajustement en temps réel des points de consigne. La seconde est une solution distribuée qui détermine de nouvelles lois de contrôle locales primaires pour les différents actionneurs. L’efficacité des deux architectures de contrôle a été validée par simulation sur un modèle de micro-réseau de référence
This work focuses on the control of a grid-interactive micro-grid to provide ancillary services to a weak power system, and more particularly a primary frequency and voltage response at the point of common coupling (PCC). The first objective of this thesis is to supervise a micro-grid in order to ensure stable operation while enforcing the economic objectives defined by an external optimizer.Then, a novel three-step methodology has been developed. First, to provide the ancillary services at the PCC, it is necessary to estimate and coordinate the flexibility of heterogeneous equipment such as distributed generators, renewables, storages, etc. An optimization algorithm is proposed for the aggregation of these flexibilities to deduce the maximum active and reactive power flows that the micro-grid can provide. The second step determines the possible behavior of the micro-grid at its PCC. Finally, two new control algorithms have been developed to ensure a droop-like behavior at the PCC. A first solution, based on a centralized Model Predictive Control based supervisor, ensures a real-time adjustment of the set-points. The second one is a distributed solution that determines new primary local control laws for DERs. The effectiveness of the two control architectures has been validated by simulation with a benchmark micro-grid model