In our independent work, the purpose for us is to gain an increased insight into the complex collaboration that exists between educators and guardians and to gain an increased insight into the relationship between educator and student. We believe that this is not a sufficiently explored topic in the after-school center and the challenge therefore lies in finding suitable literature that relates to our independent work. In this independent work, we start from our professional experiences in two difficult-to-assess dilemmas in school and leisure activities. Christopher's dilemma text is about his empathy for "his" student, and that Christopher chooses to tell a white lie to his student's mother to protect the student in question. Fredrik's dilemma text is similar to Christopher's, but the action differs from Christopher's text. Fredrik chooses to tell the truth to “his” student's mother in the belief of being able to see things in a larger perspective and thus create better conditions for the student's schooling. In our independent work, we have used methods such as: scientific essay writing and hermeneutic approach. The theories we have chosen to use are the relationship between educator and student, the relationship between school and home and ethical perspectives. We have then linked the theory part to our individual and joint reflections. Our study deals with the asymmetric versus the symmetrical relationships that exist between adults and children and the interpretive preference that adults have. We discuss the UN Convention on the Rights of the Child and how complex it is to decide what is in the best interests of the child and who can decide it. In the theory part that deals with the relationship between school and home, we highlight the problematic collaboration that exists between educators and guardians. We also highlight the collaboration with an intercultural perspective where cultures and traditions have a great impact. In the study, we write about how we can work to achieve a better collaboration with the homes. We also shed light on the concept of practical knowledge and how it can be expressed in our professional profession. Finally, in the theory part, we deal with ethics of duty, ethics of discourse, ethics of utility and ethics of proximity. At the end of our independent work, we write about our lessons from the study and concluding thoughts about what we learned during the work. Keywords: collaboration, communication, ethics, asymmetric / symmetrical relationship, leisure center, school, trust, dialogue, relationship competence, practical knowledge. / I vårt självständiga arbete är syftet för oss att få en ökad insikt i den komplexa samverkan somfinns mellan pedagoger och vårdnadshavare samt att få en ökad insikt i relationen mellan pedagog och elev. Vi anser att detta inte är ett tillräckligt utforskat ämne inom fritidshemmet och utmaningen ligger därför i att hitta lämplig litteratur som rör vårt självständiga arbete. I detta självständiga arbete utgår vi från våra yrkeserfarenheter i två svårbedömda dilemman inom skol- och fritidsverksamheten. Christophers dilemmatext handlar om hans empati för ”sin” elev, och att Christopher väljer att dra en vit lögn för sin elevs mamma för att skydda eleven ifråga. Fredriks dilemmatext är snarlik Christophers men handlandet skiljer sig från Christophers text. Fredrik väljer att berätta sanningen för ”sin” elevs mamma i tron om att kunna se saker i ett större perspektiv och således skapa bättre förutsättningar för elevens skolgång. I vårt självständiga arbete har vi använt oss av metoder som: vetenskapligt essäskrivande och hermeneutiskt förhållningssätt. De teorier som vi valt att använda oss av är relationen mellan pedagog och elev, relationen skola och hem samt etiska perspektiv. Teoridelen har vi sedan kopplat till våra individuella och gemensamma reflektioner. Vår studie behandlar de asymmetriska kontra de symmetriska relationerna som finns mellan vuxna och barn samt det tolkningsföreträde som vuxna har. Vi diskuterar kring FN:s barnkonvention och hur komplext det är att avgöra vad som är barnets bästa och vem som kan besluta det. I teoridelen som behandlar relationen skola och hem belyser vi det problematiska samarbetet som finns mellan pedagoger och vårdnadshavare. Vi belyser även samarbetet med ett interkulturellt perspektiv där kulturer och traditioner har en stor påverkan. I studien skriver vi om hur vi kan arbeta för att nå ett bättre samarbete med hemmen. Vi belyser även begreppet praktisk kunskap och hur det kan ta sig i uttryck i vår yrkesprofession. Avslutningsvis i teoridelen behandlar vi pliktetik, diskursetik, nyttoetik och närhetsetik. I slutet av vårt självständiga arbete skriver vi om våra lärdomar från studien samt avslutande tankar kring vad vi lärt oss under arbetets gång.

The main circuit equipment in an HVDC station must be rated for continuous operation as well as for stresses during ground faults and other short circuits. The component impedances are thus selected for proper operation during both continuous operation and short circuit events. Normally, Electromagnetic Transient (EMT) simulations are performed for the short circuit current ratings, which can leadto time consuming iterations for the optimization of impedance values. Hence, sufficiently correct and handy formulas are useful. For that reason, in this research work, firstly, a thorough literature study is done to gain a deep understanding of the modular multilevel converter (MMC) and its behaviour after aDC pole-to-pole short circuit fault. Two associated simulation models are designed in PSCAD/EMTDC simulation software. The focus of this thesis is on DC pole-topoleshort circuit in Symmetric Monopole HVDC VSC Modular Multilevel Converter (MMC). The desired analytical expression for the steady state fault current is determined byusing mesh analysis and also by applying KCL and it is verified by doing a set of simulations in PSCAD. A detailed sensitivity study has been done in the PSCAD simulation software to understand the influence of the AC converter reactor inductance and the DC smoothing reactor inductance on the steady state as well as peak fault current respectively. From the sensitivity study, the simulated values of peak factor have been obtained. By means of the ratio in between DC side inductance (L_DC) and AC side inductance (L_AC), and by performing a number of calculations, the desired expression for the peak factor is derived. As a result, the peak fault current can be calculated. The calculated value of the peak fault current from the derived formula is compared to the simulated value and validated. An over-estimation is considered for the rating of the equipment. Along with that, the analysis of the effect of impedances of equipment and systems are done and also verified, to better judge the accuracy of the result. In the result, it is found that, the error margin obtained from the derived analytical expression for the steady state value is within 2% of the PSCAD simulated value, which means the error can be safely ignored. Similarly, the value obtained from the derived formula for the peak fault current is within 4% over-estimation margin of the PSCAD simulated value, which is quite good in terms of cost estimation for the rating of the components.

We consider a mechanistic non-linear machine learning approach to learning signals in financial time series data. A modularised and decoupled algorithm framework is established and is proven on daily sampled closing time-series data for JSE equity markets. The input patterns are based on input data vectors of data windows preprocessed into a sequence of daily, weekly and monthly or quarterly sampled feature measurement changes (log feature fluctuations). The data processing is split into a batch processed step where features are learnt using a Stacked AutoEncoder (SAE) via unsupervised learning, and then both batch and online supervised learning are carried out on Feedforward Neural Networks (FNNs) using these features. The FNN output is a point prediction of measured time-series feature fluctuations (log differenced data) in the future (ex-post). Weight initializations for these networks are implemented with restricted Boltzmann machine pretraining, and variance based initializations. The validity of the FNN backtest results are shown under a rigorous assessment of backtest overfitting using both Combinatorially Symmetrical Cross Validation and Probabilistic and Deflated Sharpe Ratios. Results are further used to develop a view on the phenomenology of financial markets and the value of complex historical data under unstable dynamics.

Oberschwingungen als ein Merkmal der Elektroenergiequalität gewinnen durch die starke Netzintegration leistungselektronisch geregelter Anlagen wie Windenergieanlagen und nichtlineare Lasten zunehmend an Bedeutung. Bestehende Normen entsprechen nicht den zukünftigen Erfordernissen des Elektroenergiesystems und bedürfen diesbezüglich einer Überarbeitung. In der Arbeit werden wesentliche Einflussfaktoren auf das Oberschwingungsverhalten von Windparks identifiziert, beschrieben und modelliert. Dabei wird der stochastische Charakter der Oberschwingungen mithilfe von probabilistischen Ansätzen erfasst. Des Weiteren wird ein neuer Ansatz zur Untersuchung der Wechselwirkung zwischen dem Windpark und dem vorgelagerten Netz entwickelt. Der Ansatz ermöglicht, die vom Windpark verursachte Änderung der Oberschwingungsspannung am Netzanschlusspunkt zu ermitteln. Diese Arbeit liefert einen Beitrag zur Verbesserung bestehender Normen für die Anbindung von Windparks. / Harmonics, as one of the power quality criteria, are increasingly gaining attention due to the progressive contribution of renewable energy resources and the application of the nonlinear load in the power system. Current standards do not conform to the future requirements of the power system, thus requiring a revision. In this work, main influence factors on the harmonic behavior of wind farms are identified, explained, and modelled. Thereby, the stochastic nature of harmonics is taken into account using probabilistic approaches. Moreover, a novel approach is developed to investigate the interaction between the wind farm and the upstream grid. With the aid of this approach, it is possible to determine the voltage change caused by the wind farm at the point of connection. This work contributes to improve the existing standards for the connection of wind farms.

Der Beitrag verfolgt die Entwicklung der Skrjabin’schen Harmonik von dessen Früh- bis zu dessen Spätwerk. Ausgehend vom der Struktur des Einzelklangs (›Chopin-Akkord‹, ›Skrjabin-Akkord‹) werden die Tendenzen aufgezeigt, die folgerichtig ein neues Klangfortschreitungssystem nach sich ziehen. Der äquidistante Quintenzirkel wird durch andere, ebenfalls äquidistante Zirkel ersetzt. Es entstehen symmetrische Tonsysteme, an die später u.a. Olivier Messiaen anknüpft. Als entscheidend gilt dem Autor die Idee der ›Verdichtung‹ – ein Begriff, den Sigmund Freud in seiner Theorie der Traumdeutung ausgearbeitet hat. In dessen Sinne wird die Klangsprache Skrjabins als Verdichtungsarbeit interpretiert. / This article traces the development of Scriabin’s harmonic practice from his early work to his late work. Proceeding from the structure of individual chords (e.g., the “Chopin chord,” the “Scriabin chord”), tendencies will be shown that consequently lead to a new system of harmonic progression: the equidistant circle of fifths is replaced by other circles that are also equidistant. The result is symmetrical tone-systems that later influence Olivier Messiaen, among others. The author places special emphasis on the idea of “condensation” (Verdichtung), a term developed by Sigmund Freund in his theorizing of the interpretation of dreams. In this sense Scriabin’s harmonic language is thus interpreted as a process of condensation.

No description available.

Les énergies renouvelables, l’énergie sous la forme électrique et son transport à l’aide de réseaux électriques intelligents représentent aujourd’hui des enjeux majeurs car ils ont de grands impacts environnementaux et sociétaux. Ainsi, la production, le transport et la gestion de l’énergie électrique, continuent toujours à susciter un intérêt croissant. Pour atteindre ces objectifs, plusieurs verrous technologiques doivent être levés. Au-delà des questions liées aux architectures des réseaux électriques, aux modèles, aux outils de dimensionnement, à la formalisation de caractéristiques et d’indicateurs, aux contraintes et aux critères, à la gestion et à la production décentralisée, la qualité de la puissance électrique est centrale pour la fiabilité de l’ensemble du système de distribution. Les perturbations affectent la qualité des signaux électriques et peuvent provoquer des conséquences graves sur les autres équipements connectés au réseau. Les travaux de cette thèse s’inscrivent dans ce contexte et de fait ils sont orientés vers le développement de modèles, d’indicateurs et de méthodes de traitement des signaux dédiés à la surveillance en temps-réel des performances des réseaux de distribution électrique.Cette thèse analyse la qualité de la puissance électrique, en prenant en compte plusieurs caractéristiques bien connues ainsi que leur pertinence. Les modèles des systèmes électriques et les méthodes de traitement du signal pour estimer leurs paramètres sont étudiés pour des applications en temps-réel de surveillance, de diagnostic et de contrôle sous diverses conditions. Parmi tous, la fréquence fondamentale est l’un des paramètres les plus importants pour caractériser un système de distribution électrique. En effet, sa valeur qui est censée être une constante, varie en permanence et reflète la dynamique de l’énergie électrique disponible. La fréquence peut également être affectée par certaines productions d’énergie renouvelable et peut être influencée par des mauvaises synchronisations de certains équipements. En outre, la puissance absorbée par les charges ou produite par des sources est généralement différente d’une phase à l’autre. Évidemment, la plupart des installations électriques existantes avec plusieurs phases, qu’elles soient résidentielles ou industrielles, travaillent dans des conditions déséquilibrées. Identifier les composantes symétriques de tension est dans ce cas un moyen pertinent pour quantifier le déséquilibre entre les phases d’un système électrique.De nouvelles représentations de type espace d’état et modélisant des systèmes électriques sont proposées pour estimer la fréquence fondamentale et pour identifier les composantes symétriques de tension des systèmes électriques triphasés et déséquilibrés. Le premier modèle d’espace d’état proposé considère la fréquence fondamentale comme connue ou obtenue par un autre estimateur. En contrepartie, il fournit les autres paramètres caractérisant le système électrique. Un second modèle d’état-espace est introduit. Il est original dans le sens où il ne nécessite aucune connaissance de la fréquence fondamentale. Une de ses variables d’état est directement reliée à la fréquence et permet donc de la déduire. En outre, ce nouvel espace d’état est parfaitement capable de représenter des systèmes électriques à trois phases équilibrés et non équilibrés. [...] / Renewable energy, electricity and smart grids are core subjects as they have great environmental and societal impacts. Thus, generating, transporting and managing electric energy, i.e., power, still continue to drive a growing interest. In order to properly achieve these goals, several locks must be removed. Beyond issues related to the distribution architecture, the formalization of models, sizing tools, features and indicators, constraints and criteria, decentralized generation and energy management, power quality is central for the whole grid’s reliability. Disturbances affect the power quality and can cause serious impact on other equipment connected to the grid. The work of this thesis is part of this context and focuses on the development of models, indicators, and signal processing methods for power quality monitoring in time-varying power distribution systems.This thesis analyzes the power quality including several well-known features and their relevance. Power system models and signal processing methods for estimating their parameters are investigated for the purpose of real-time monitoring, diagnostic and control tasks under various operating conditions. Among all, the fundamental frequency is one of the most important parameters of a power distribution system. Indeed, its value which is supposed to be a constant varies continuously and reflects the dynamic availability of electric power. The fundamental frequency can also be affected by renewable energy generation and by nasty synchronization of some devices. Moreover, the power absorbed by loads or produced by sources is generally different from one phase to the other one. Obviously, most of the existing residential and industrial electrical installations with several phases work under unbalanced conditions. Identifying the symmetrical components is therefore an efficient way to quantify the imbalance between the phases of a grid. New state-space representations of power systems are proposed for estimating the fundamental frequency and for identifying the voltage symmetrical components of unbalanced three-phase power systems. A first state-space representation is developed by supposing the fundamental frequency to be known or to be calculated by another estimator. In return, it provides other parameters and characteristics from the power system. Another original state-space model is introduced which does not require the fundamental frequency. Here, one state variable is a function of the frequency which can thus be deduced. Furthermore this new state-space model is perfectly are able to represent a three-phase power system in both balanced and unbalanced conditions. This not the case of lots of existing models. The advantage of the proposed state-space representation is that it gives directly access to physical parameters of the system, like the frequency and the amplitude and phase values of the voltage symmetrical components. Power systems parameters can thus be estimated in real-time by using the new state-space with an online estimation process like an Extended Kalman Filter (EKF). The digital implementation of the proposed methods presents small computational requirement, elegant recursive properties, and optimal estimations with Gaussian error statistics.The methods have been implemented and validated through various tests respecting real technical constraints and operating conditions. The methods can be integrated in active power filtering schemes or load-frequency control strategies to monitor power systems and to compensate for electrical disturbances.

Text in English, abstract in English, Afrikaans and Venda / This study developed and tested an integrated internal communication audit (IICA) tool to evaluate the communication strengths and weaknesses of the Unisa Library. The existing communication audit instruments were explored, namely: the Communication Satisfaction Questionnaire (CSQ) and the International Communication Association (ICA) audit were adapted and complemented by the Organisational Culture Survey (OCS) and the Critical Incident Technique (CIT). The current trends and the trends in South Africa were also explored. The sequential mixed method design consisting of the semi-structured qualitative interviews and the quantitative surveys were used to collect data. The ATLAS.ti and the Statistical Package for Social Sciences (SPSS) software packages were used to analyse qualitative and quantitative data. The results revealed the IICA as an appropriate tool for measuring the integrated internal communication of the Unisa Library. The IICA identified the communication needs of employees; the active and preferred communication channels; and the positive and negative communication experiences of employees. / Hierdie studie het ʼn geïntegreerde interne kommunikasie-oudit (IICA)-hulpmiddel ontwikkel en getoets om kommunikasie-sterkpunte en -swakhede van die Unisa-biblioteek te evalueer. Die bestaande kommunikasie-oudit-instrumente was ondersoek, naamlik: die Kommunikasietevredenheidsvraelys (CSQ) en die Internasionale Kommunikasievereniging (ICA) se oudit is aangepas en gekomplementeer deur die Organisasiekultuur-opname (OCS) en die Kritiese-insident-tegniek (CIT). Die sekwensiële gemengdemetode-ontwerp, bestaande uit die halfgestruktureerde kwalitatiewe onderhoude en die kwantitatiewe opnames, is gebruik om data in te samel. Die ATLAS.ti-programmatuurpakket en die Statistiese Pakket vir Sosiale Wetenskappe (SPSS)-programmatuur is gebruik om kwalitatiewe en kwantitatiewe data te ontleed. Die resultate gewys die IICA as ʼn geskikte hulpmiddel was in die meting van die geïntegreerde interne kommunikasie van die Biblioteek. Die IICA geïdentifiseer die kommunikasie behoeftes van werknemers; die aktiewe en voorkeur kommunikasie kanale; en die positiewe en negatiewe kommunikasie ervarings van werknemers. / Ngudo iyi yo bveledza na u linga tshishumiswa tsha u Sedzulusa Vhudavhidzani ha nga ngomu ho Ṱanganelaho (Integrated Internal Communication Audit (IICA), u ṱola vhuḓi na vhuvhi ha vhudavhidzani kha Ḽaiburari ya Univesithi ya Afrika Tshipembe. Zwishumiswa zwa u sedza vhudavhidzani zwi re hone zwo sedzuluswaho zwi katela: Mbudzisambekanywa dza Vhudavhidzani dzine dza fusha ṱhoḓea (Communication Satisfaction Questionnaire) (CSQ) na tshishumiswa tsha u sedzulusa vhudavhidzani tsha Dzangano ḽa Dzitshaka ḽa Vhudavhidzani (International Communication Association) (ICA). Zwishumiswa izwo zwo ḓadziswa nga tshishumiswa tsha Ṱhoḓisiso ya Mvelele ya Tshiimiswa (Organisational Culture Survey) (OCS) na Tshikalo tsha u ela Maitele a Zwithu zwa ndeme (Critical Incident Technique) (CIT). Pulane ya thevhekano ya maitele o ṱanganelaho o vhumbwaho nga maitele a ṱhoḓisiso ane a shumiswa kha saintsi dza matshilisano (qualitative) na maitele a ṱhoḓisiso ane a shumisa zwiṱatisiṱika na mbalo (quantitative) zwo shumiswa u kuvhanganya mawanwa. Phakhedzhi ya Sofuthiwea ya ATLAS.ti na phakhedzhi ya Siṱatisiṱika ya Saintsi dza Matshilisano (Statistical Package for Social Sciences - SPSS) dzo shumiswa u saukanya mawanwa a ṱhoḓisiso dza matshilisano na a ṱhoḓisiso dza zwiṱatisiṱika na mbalo. Mvelelo dzo bvisela khagala uri IICA ndi tshishumiswa tsho teaho u ela vhudavhidzani ho ṱanganelaho ha nga ngomu Ḽaiburari ya Univesithi ya Afrika Tshipembe. Tshishumiswa itshi tsho bvisela khagala thoḓea dza vhashumi dza vhudavhidzani, zwishumiswa zwa vhudavhidzani zwine zwa khou shumiswa na zwi takalelwaho; na tshenzhemo ya vhashumi kha vhudavhidzani havhudi and vhu si havhudi. / Communication Science / M. Comm (Communication Science)

L’extensa implantació del control digital als entorns industrials, científics, comercials, professionals i domèstics ha revelat, d’ençà dues dècades, la gran sensibilitat d’aquests dispositius davant sobtats i breus descensos de tensió al subministrament elèctric de xarxa: aturades de plantes a processos productius, re – arrancades a processadors i sistemes de telecomunicació, etc.; i la causa sol esdevenir aparentment inexplicable pels usuaris. La normalització de les conseqüències, però, pot equivaler a un dia sencer de producció nul•la. L’ínfima correlació mostrada pels fenòmens esmentats amb anomalies al sistema elèctric proper (un client pot patir sèries conseqüències, per bé que el client veí només ha percebut una oscil•lació a l’enlluernat, i tots dos comparteixen la mateixa escomesa) sumada amb l’absència contrastada d’interrupció elèctrica suposà, al començament, un major grau d’incertesa, no només pels consumidors; també per a les empreses elèctriques. Fou necessari analitzar el problema en les seves vessants “microscòpica” i “macroscòpica” per a determinar la causa eficient: registrar la forma d’ona al punt de subministrament afectat i fer l’inventari de tots els incidents al Sistema Elèctric del mateix moment. La causa: els sots de tensió produïts per incidents elèctrics a xarxes remotes respecte el subministrament. Davallades sobtades (entre el 80 i el 10% del valor nominal) i ràpides (entre 10 ms i 1 s) al valor eficaç de la tensió subministrada, sense pas per “Zero”, produïdes, principalment, per curt - circuits perfectament detectats i eliminats a xarxes d’Alta Tensió (AT), molt allunyats de la conseqüència observada. A Catalunya, hom comptabilitzen afectacions davant curt - circuits a les interconnexions amb l’Aragó, Castelló i França. La present Tesi Doctoral estableix: • La metodologia per a modelar el Sistema Elèctric de Potència; • La sistematització del binomi causa (curt - circuit) – efecte (sot de tensió); • La personalització estadística de risc pel sot de tensió segons comarques; • Un sistema de protecció eficaç per a limitar la durada dels sots. La metodologia ha estat enfocada a la utilització sistemàtica, tal que per a cada curt - circuit esdevingut a la xarxa AT es pugui establir, en temps real, las capçaleres de subministrament afectades pel sot de tensió, així com la magnitud i la durada del mateix. L’entorn d’aplicació triat ha estat el Sistema Elèctric de Catalunya, per bé que la metodologia i sistemàtica són exportables, de forma natural, a qualsevol altre sistema elèctric trifàsic de corrent altern. / La implantación masiva del control digital en entornos industriales, científicos, comerciales, profesionales y domésticos ha puesto de manifiesto, durante los últimos veinte años, la gran sensibilidad de los mismos ante súbitos y breves descensos de tensión en la alimentación eléctrica procedente de la red: paradas de planta en procesos productivos, re – arranques en procesadores y sistemas de telecomunicación tienen lugar; y la causa de los mismos suele ser aparentemente inexplicable para los usuarios. La normalización de las consecuencias, en ocasiones, equivale a un día de producción nula. La escasa correlación mostrada por dichos fenómenos con anomalías en el sistema eléctrico cercano (un cliente padece consecuencias serias, mientras que el cliente vecino solamente ha percibido una oscilación en el alumbrado y ambos se alimentan del mismo tramo eléctrico) sumada con la ausencia contrastada de interrupción eléctrica supuso, en los inicios, un mayor grado de incertidumbre tanto para los consumidores como para las empresas eléctricas. Fue necesario analizar el problema a nivel “microscópico” y “macroscópico” para determinar la causa eficiente: registrar la forma de onda en el punto de suministro afectado y revisar todos los incidentes habidos en el Sistema Eléctrico en dicho instante. La causa: los huecos de tensión producidos por incidentes eléctricos en redes alejadas del suministro. Descensos súbitos (entre el 80 y el 10% del valor nominal) y rápidos (entre 10 ms y 1 s) en el valor eficaz de la tensión suministrada, sin paso por “cero” de la misma, producidos, principalmente, por cortocircuitos perfectamente detectados y eliminados en redes de Alta Tensión (AT), y situados muy lejos de la consecuencia observada. En el caso de Catalunya, se han contabilizado afectaciones ante cortocircuitos en interconexiones con Aragón, Castellón de la Plana y Francia. La presente Tesis Doctoral establece: • La metodología para modelar el Sistema Eléctrico de Potencia; • La sistematización para el binomio causa (cortocircuito) – efecto (hueco); • La personalización del riesgo estadístico de hueco vs. comarcas; • Un sistema protectivo eficaz para limitar duración de los huecos. Dicha metodología se ha orientado a la utilización sistemática, tal que para cada cortocircuito que tenga lugar en la red AT pueda establecerse, en tiempo real, las cabeceras de suministro afectadas por hueco de tensión, la magnitud y la duración del mismo. Como entorno de aplicación, se ha utilizado el Sistema Eléctrico de Catalunya, si bien la metodología y sistematización son exportables, de forma natural, a cualquier otro sistema eléctrico trifásico de corriente alterna. / The massive introduction of digital control in industrial, scientific, commercial, professional and domestic environments has revealed, over the last twenty years, the great sensitivity of them to sudden and short voltage dips in the electrical power grid: shutdowns of productive process plants, re - starts of processors and telecommunications systems take place, and the cause of them is often apparently inexplicable to the users. The normalization of the consequences sometimes is equivalent to a day without production. The weak correlation shown by these phenomena with anomalies in the nearby electrical system (i.e. in the same portion of a common distribution network, a customer may suffer serious consequences, while the adjacent customer has only percept a swing in the lighting) together with the absence of electrical power interruption represented, in the beginning, a great degree of uncertainty for both consumers and utilities. It was necessary to analyze the problem at the "microscopic" and "macroscopic" levels to determine the efficient cause: record the waveform at the affected plants and review all the disturbances occurred in the Power System at the same instant of time. The cause: voltage dips caused by electrical disturbances away from the supply. Sudden decreases (between 80 and 10% of the nominal value) and fast (between 10 ms and 1 s) in the supplied rms voltage, produced mainly by short-circuits perfectly detected and eliminated in High Voltage (HV) networks, and located far away from the observed consequence. In the case of Catalonia, affectations due to short-circuits in interconnects with Aragon, Castellón de la Plana and France have been recorded. This thesis provides: • A methodology useful to model the Power System; • A systematic analysis for cause – effect: from short – circuit to voltage dip; • A particularization voltage dip statistic risk for each county; • A reliable protective system to ensure time – limitation for voltage dips. The presented methodology is oriented to the systematic use, such that for every short - circuit that takes place in the HV network, the magnitude and duration of voltage dips that appear in the distribution can be established in real-time. As the application framework, the Catalan Power System is used, although the methodology and systematization are exportable, to any other alternating three-phase power system.

This thesis deals with the modeling, analysis and control of a novel brushlessgenerator for wind power application. The generator is named as rotatingpower electronic brushless doubly-fed induction machine/generator (RPEBDFIM/G). A great advantage of the RPE-BDFIG is that the slip power recoveryis realized in a brushless manner. This is achieved by introducing an additionalmachine termed as exciter together with the rotating power electronicconverters, which are mounted on the shaft of a DFIG. It is shown that theexciter recovers the slip power in a mechanical manner, and delivers it backto the grid. As a result, slip rings and carbon brushes can be eliminated,increasing the robustness of the system, and reducing the maintenance costsand down-time of the turbine. To begin with, the dynamic model of the RPE-BDFIG is developed andanalyzed. Using the dynamic model, the working principle of the generatoris understood and its operation explained. The analysis is carried out atspeeds, ±20% around the synchronous speed of the generator. Moreover, thedynamics of the generator due to external load-torque disturbances are investigated.Additionally, the steady-state model is also derived and analyzed forthe machine, when operating in motor mode. As a next step, the closed-loop control of the generator is considered indetail. The power and speed control of the two machines of the generator andthe dc-link voltage control is designed using internal model control (IMC)principles. It is found that it is possible to maintain the stability of thegenerator against load-torque disturbances from the turbine and the exciter,at the same time maintain a constant dc-link voltage of the rotor converter.The closed-loop control is also implemented and the operation of the generatorwith the control theory is confirmed through experiments.In the third part of the thesis, the impact of grid faults on the behaviourof the generator is investigated. The operation of the generator and its responseis studied during symmetrical and unsymmetrical faults. An approachto successful ride through of the symmetrical faults is presented, using passiveresistive network (PRN). Moreover, in order to limit the electrical and mechanicaloscillations in the generator during unsymmetrical faults, the dualvector control (DVC) is implemented. It is found that DVC to a certain extentcan be used to safeguard the converter against large oscillations in rotorcurrents. Finally, for completeness of the thesis, a preliminary physical design ofthe rotating power electronic converter has been done in a finite elementsoftware called ANSYS. The thermal footprint and the cooling capability,with estimates of the heatsink and fan sizes, are presented. Besides, another variant of a rotating electronic induction machine whichis based on the Lindmark concept and operating in a single-fed mode is also investigated. It’s steady-state model is developed and verified through experiments. / <p>QC 20151006</p>