The dissertation studies the nonlinear resonance problems of power systems. Generally speaking, ferroresonance has usually occurred in low-voltage distribution system, especially for potential transformers. Due to the considerable increase of power consumption, the power system is more complex than before. Besides, a number of under-ground cables are used, and transformers¡¦ loss reduce due to improvement of core iron material. These factors could probably result in ferroresnance occurring in extra-high-voltage power system. The dissertation proposed three-phase representation method to analyze unbalance and non-linear system. This method employ magnetically coupled electrical circuit techniques and the original voltage equations can be used without the need for any transformations, which improves significantly computation accuracy. Consequently, it is quite suitable for power system design and incident investigation. Since the traditional d-q-0 model is not well suited for the study of unbalanced faults and requires further transformation, the analytical solution becomes rather complicated and the solutions are still inaccurate. At last we simulated the ferroresonant overvoltages occurring at a nuclear power station in Taiwan in order to investigate the causes and afford mitigation. The simulation results were enough to prove accuracy and practicability of this method.

Η παρούσα διπλωματική εργασία πραγματεύεται την μελέτη και το σχεδιασμό μιας τριφασικής ανορθωτικής διάταξης με την οποία επιτυγχάνεται διόρθωση του συντελεστή ισχύος. Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Κύριος σκοπός αυτής της διπλωματικής εργασίας είναι η κατασκευή ενός μετατροπέα ανόρθωσης ανύψωσης ο οποίος λειτουργεί σε ασυνεχή αγωγή και μπορεί να τοποθετηθεί στην έξοδο μιας ανεμογεννήτριας σαν πρώτο στάδιο σύνδεσης με το δίκτυο. Απώτερος σκοπός είναι η πειραματική επιβεβαίωση της θεωρίας καθώς και του μηχανισμού με τον οποίο επιτυγχάνεται η διόρθωση του συντελεστή ισχύος. Αρχικά γίνεται μια γενική αναφορά στην έννοια της ποιότητας ισχύος, τα χαρακτηριστικά της μεγέθη, το συντελεστή ισχύος και τις ανώτερες αρμονικές. Επίσης αναφέρονται βασικές τριφασικές ανορθωτικές διατάξεις με διορθωμένο συντελεστή ισχύος ενώ γίνεται και μια γενική αναφορά στα αιολικά συστήματα, τον τρόπο λειτουργίας τους και την σύνδεση τους με το δίκτυο. Στη συνέχεια, αναλύεται η λειτουργία του μετατροπέα που κατασκευάστηκε κατά την διάρκεια αυτής της διπλωματικής εργασίας, δηλαδή τριφασικής διάταξης ανόρθωσης-ανύψωσης με ένα διακοπτικό στοιχείο, που λειτουργεί στην περιοχή ασυνεχούς αγωγής (DCM). Ο μετατροπέας αυτός θα δέχεται πολική τάση στην είσοδο του 40-100V, ανυψώνοντας την στα 350V στην έξοδο. Παράλληλα το ρεύμα εισόδου έχει μικρό αρμονικό περιεχόμενο επιτυγχάνοντας έναν υψηλό συντελεστή ισχύος. Το επόμενο βήμα είναι η μοντελοποίηση και η προσομοίωση του μετατροπέα σε περιβάλλον Matlab/Simulink έτσι ώστε να εξακριβωθεί η ορθή λειτουργία του σύμφωνα με τη θεωρητική ανάλυση. Τέλος, μελετάται και κατασκευάζεται στο εργαστήριο η πειραματική διάταξη με την οποία διεξάγονται μετρήσεις για την επιβεβαίωση και αξιολόγηση της θεωρητικής μελέτης. / In this diploma thesis the analysis and design of a three phase rectifier achieving high power factor are presented. This work was developed in the Laboratory of Electromechanical Energy Conversion at the Department of Electrical Engineering and Computer Technology of the Polytechnic School, University of Patras, Greece. The main purpose of this diploma thesis is the implementation of a Power Factor Correction Three Phase Rectifier operated in Discontinuous Current Mode (DCM) which can be used as a first stage for the connection of a small wind turbine to the grid. Through this work, the theoretical analysis and the mechanism that achieves the high power factor are verified through the implementation of a laboratory prototype. Initially, the concepts of power quality, power factor and high order harmonics are explained. Furthermore, some common power factor correction rectifier topologies are reported as well as a reference on wind turbines, their operation and their connection to the grid. Secondly, the working principle of the Single Switch Power Factor Correction DCM Boost Rectifier is presented. This converter is designed to rectify and boost the voltage of a small wind turbine, varying between 40 and 100V line to line rms, to 350Vdc. In addition the converter’s input current presents low harmonic distortion which results in a high power factor. The following step is to model and simulate the converter in Matlab/Simulink in order to verify its operation based on the theoretical analysis. Finally, a laboratory prototype is designed and implemented, on which experiments are conducted, in order to verify and evaluate the theoretical study.

Τα τελευταία 35 χρόνια έχει προκύψει ένα ενεργειακό πρόβλημα το οποίο μας επιβάλει να αλλάξουμε την ενεργειακή μας αντίληψη. Το πετρέλαιο αλλά και άλλα ορυκτά καύσιμα έχουν πεπερασμένα αποθέματα και η χρήση τους επιβαρύνει το περιβάλλον. Επίσης γεωπολιτικά συμφέροντα δεν επιτρέπουν την ανεμπόδιστη διανομή του. Μέσα σε αυτό το κλίμα της ενεργειακής απεξάρτησης από τα ορυκτά καύσιμα αναπτύσσονται τα τελευταία χρόνια τα υβριδικά οχήματα. Τα ηλεκτρικά υβριδικά οχήματα είναι ένα μεταβατικό στάδιο από την πετρελαιοκίνηση στην εξ’ ολοκλήρου κίνηση μέσω ηλεκτρισμού από ενεργειακές κυψέλες. Αποτελούνται από έναν συμβατικό κινητήρα εσωτερικής καύσης και μια ηλεκτρική μηχανή, η οποία τροφοδοτείται από συσσωρευτές. Τα υβριδικά οχήματα χωρίζονται σε διάφορες κατηγορίες ανάλογα με τις τεχνολογίες υβριδοποίησης που διαθέτουν και την διάταξη του ηλεκτρομηχανολογικού τους συστήματος. Στόχος της παρούσας διπλωματικής εργασίας (η οποία είναι η συνέχεια δυο προηγούμενων) είναι η προσπάθεια κατασκευής ενός υβριδικού αυτοκινήτου. Για να γίνει αυτό εφικτό απαιτούνται, ένα όχημα το οποίο να μπορεί να δεχθεί εύκολα μηχανολογικές μετατροπές, ένας ηλεκτρικός κινητήρας και συσσωρευτές. Ο ηλεκτρικός κινητήρας ελέγχεται από έναν αντιστροφέα. Ο αντιστροφέας είναι μια ηλεκτρική συσκευή η οποία μετατρέπει το συνεχές ρεύμα των συσσωρευτών σε εναλλασσόμενο. Βασικό κομμάτι του αντιστροφέα είναι η λογική παλμοδότησής του. Ο αντιστροφέας που κατασκευάστηκε χρησιμοποιεί τον άμεσο έλεγχο ροπής, ο οποίος είναι ένα είδος άμεσου διανυσματικού ελέγχου που χρησιμοποιεί τον μετασχηματισμό Park. / Τα τελευταία 35 χρόνια έχει προκύψει ένα ενεργειακό πρόβλημα το οποίο μας επιβάλει να αλλάξουμε την ενεργειακή μας αντίληψη. Το πετρέλαιο αλλά και άλλα ορυκτά καύσιμα έχουν πεπερασμένα αποθέματα και η χρήση τους επιβαρύνει το περιβάλλον. Επίσης γεωπολιτικά συμφέροντα δεν επιτρέπουν την ανεμπόδιστη διανομή του. Μέσα σε αυτό το κλίμα της ενεργειακής απεξάρτησης από τα ορυκτά καύσιμα αναπτύσσονται τα τελευταία χρόνια τα υβριδικά οχήματα. Τα ηλεκτρικά υβριδικά οχήματα είναι ένα μεταβατικό στάδιο από την πετρελαιοκίνηση στην εξ’ ολοκλήρου κίνηση μέσω ηλεκτρισμού από ενεργειακές κυψέλες. Αποτελούνται από έναν συμβατικό κινητήρα εσωτερικής καύσης και μια ηλεκτρική μηχανή, η οποία τροφοδοτείται από συσσωρευτές. Τα υβριδικά οχήματα χωρίζονται σε διάφορες κατηγορίες ανάλογα με τις τεχνολογίες υβριδοποίησης που διαθέτουν και την διάταξη του ηλεκτρομηχανολογικού τους συστήματος. Στόχος της παρούσας διπλωματικής εργασίας (η οποία είναι η συνέχεια δυο προηγούμενων) είναι η προσπάθεια κατασκευής ενός υβριδικού αυτοκινήτου. Για να γίνει αυτό εφικτό απαιτούνται, ένα όχημα το οποίο να μπορεί να δεχθεί εύκολα μηχανολογικές μετατροπές, ένας ηλεκτρικός κινητήρας και συσσωρευτές. Ο ηλεκτρικός κινητήρας ελέγχεται από έναν αντιστροφέα. Ο αντιστροφέας είναι μια ηλεκτρική συσκευή η οποία μετατρέπει το συνεχές ρεύμα των συσσωρευτών σε εναλλασσόμενο. Βασικό κομμάτι του αντιστροφέα είναι η λογική παλμοδότησής του. Ο αντιστροφέας που κατασκευάστηκε χρησιμοποιεί τον άμεσο έλεγχο ροπής, ο οποίος είναι ένα είδος άμεσου διανυσματικού ελέγχου που χρησιμοποιεί τον μετασχηματισμό Park.

The hardware validation of a novel average-value model (AVM) for the simulation of a synchronous-generator/controlled rectifier system is presented herein. The generator is characterized using genetic algorithm techniques to fit standstill frequency response (SSFR) measurements to q and d-axis equivalent circuits representing the generator in the rotor reference frame. The generator parameters form the basis of a detailed model of the system, from which algebraic functions defining the parametric AVM are derived. The average-value model is compared to the physical system for a variety of loading and operating conditions including step load change, change in delay angle, and external closed-loop control, validating the model accuracy for steady-state and transient operation.

This study concentrates on the modelling of three phase flow and miscible CO2 flooding in pore networks that captures the natural porous medium of a reservoir. That is to say, the network, that is a Matlab code, consists of different sided triangles which are located randomly through the grids. The throats that connect the pores are also created by the model. Hence, the lengths and the radii of the throats are varying. The network used in this research is assumed to be representative of mixed-wet carbonates in 2-D. Mixed wettability arises in real porous media when oil renders surfaces it comes into prolonged contact with oil-wet while water-filled nooks and crannies remain water-wet. The model developed is quasi-static approach to simulate two phase and three phase flows. By this, capillary pressures, relative permeabilities, saturations, flow paths are determined for primary drainage, secondary imbibition, and CO2 injection cases. To calculate the relative permeability, capillary entry pressures are first determined. Then, hydraulic conductances and flow rates of the network for each grid are obtained. Phase areas and saturations are also determined. It is accepted that the displacement mechanism in drainage and CO2 injection is piston-like whereas in imbibition it is either piston-like or snap-off. The results of the model are compared with the experimental data from the literature. Although, the pore size distribution and the contact angle of the model are inconsistent with the experimental data, the agreement of the relative permeabilities is promising. The effect of contact angle in the same network for three phase flow where immiscible CO2 is injected as a third phase at supercritical temperature (32 &deg / C) is investigated. And it is found that, the increase in the intrinsic angles causes decrease in relative permeability values. As another scenario, two phase model is developed in which miscible CO2 &amp / #8211 / water is flooded after the primary drainage of the same 2-D network at supercritical temperature (32 &deg / C). This case is compared with the previous case and the effects of miscibility are investigated such that it causes the relative permeability values to increase. Adsorption is another concern of which its effects are analyzed in a single pore model. The model is compared with the reported experimental data at high temperature and pressures. A reasonable fit is obtained.

O objetivo deste trabalho consiste na implementação de arquiteturas de sistema inteligentes em Processadores Digitais de Sinais (DSP) visando, sobretudo, o controle em tempo real de motores de indução trifásicos. Para tanto, propõe-se uma abordagem fuzzy para o controle de velocidade de motores de indução trifásicos baseado na metodologia de ajuste de tensão e freqüência (Volts/Hertz) proveniente de um inversor PWM, de modo que o fluxo no entreferro seja mantido constante. O enfoque principal consiste no desenvolvimento do sistema de controle em hardware considerando o estudo dinâmico do controlador frente às variações de conjugado de carga, cujo desempenho da metodologia proposta será avaliado mediante simulações computacionais e ensaios experimentais realizados em laboratório. / The objective of this work consists of the implementation of intelligent system architecture in Digital Signal Processor (DSP) aiming at the real-time three-phase induction motor control. Therefore, a fuzzy logic speed control drive system for three-phase induction motor is proposed, whereas the control methodology is based on voltage and frequency (Volts/Hertz) adjustment of a PWM inverter so that the airgap flux maintains constant. The main focus concerns about hardware development of the control system considering the controller dynamic response study in relation to load torque variations, from which the proposed methodology performance is evaluated by means of computational simulation and experimental results obtained in laboratory.

Este trabalho apresenta uma estratégia para a estimativa de velocidade do motor de indução trifásico baseada em redes neurais artificiais utilizando medidas de variáveis primárias como tensão e corrente. O uso de motores de indução trifásicos é uma constante em diversos setores industriais e de grande importância no cenário energético nacional. A maioria das metodologias de controle, acionamento e dimensionamento destes motores é fundamentada nas medidas de velocidade no eixo. Entretanto, a medida direta da velocidade compromete o sistema de controle e acionamento diminuindo sua robustez e aumentando o custo de implementação. Resultados de simulação e de ensaios experimentais para validação da proposta são também apresentados. / This work presents an approach to estimate speed in induction motors based on artificial neural networks and using measurement of primary variables like voltage and current. The use of induction motors is very common in many industrial sectors and plays an important role in the national energetic scene. The methodologies used in control, start up and dimensioning of these motors are based on measure of the speed variable. However, the direct measure of this variable compromises the system control and start up of the machine, reducing its robustness and increasing the implementation costs. Simulation results and experimental data are presented to validate the proposed approach.

Made available in DSpace on 2016-12-12T20:27:38Z (GMT). No. of bitstreams: 1 Eduardo Henrique Couto.pdf: 1926472 bytes, checksum: 2b4464d74812fd9a1dc1cf69975b8f1f (MD5) Previous issue date: 2013-12-06 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / When the three phase induction motor is vector-controlled driven, is considered the mathematical model as a set of linear equations, so that the control is more effective only over an operation point. However, when changing that point, control can pass to not respond properly, causing unwanted errors of speed, position or even instability. Such behavior are due to mismatch of the real behavior of the motor, which is non-linear and time-varying system, and the mathematical model used in the project. Thus, parametric identification techniques allow the motor parameters to be determined online, tracking its time variation. The focus of the thesis is to present a general background of the subject and show the results obtained using techniques of parametric identification, more specifically exploring the least squares method to fit the parameters of the motor in closed loop. / Quando o motor de indução trifásico é acionado em malha de controle vetorial, é considerado o modelo matemático como um conjunto de equações lineares, por isso o controle é mais efetivo somente sobre este ponto de operação. Entretanto, quando se muda esse ponto, o controle pode passar a não responder mais adequadamente, causando erros indesejáveis de velocidade, posição e até mesmo a instabilidade. Tais fatos ocorrem devido à descasamentos entre o comportamento real do motor, que é não linear e variante no tempo, e o modelo matemático utilizado para o projeto. Dentro de tal contexto, as técnicas de identificação paramétrica permitem que os parâmetros do motor sejam determinados de forma online, monitorando sua variação no tempo. O foco principal deste trabalho é apresentar um cenário geral do assunto e mostrar os resultados obtidos usando as técnicas de identificação paramétrica, mais especificamente explorando o método dos mínimos quadrados para ajustar os parâmetros do motor em malha fechada

Overview: Pregnant women living with obesity are at increased risk of pregnancy complications, with risks rising as Body Mass Index (BMI) increases. Midwives are willing to support women with managing their gestational weight gain but lack confidence and access to supporting resources. In the UK there are no interventions that aim to change the intention and behaviour of midwives, to support women with managing their gestational weight gain. The Theory of Planned Behaviour (TPB) (Ajzen, 1985) was utilised to frame the design of a behaviour change intervention for midwives. This three-phase study conducted a qualitative needs assessment, intervention design, and a quantitative study of, intervention testing. Methods: Phase One: Interview data were thematically analysed and the TPB utilised to elicit participants’ salient beliefs, to inform intervention design. Phase Two: The design of the intervention, and the TPB scale, were informed by Phase One data. Midwives reviewed the intervention and participated in a pilot test of the scale. Phase Three: The intervention was tested in a before-and-after controlled trial, utilising the refined TPB scale. Results: Phase One: 4 key themes emerged: 1)The current state of affairs 2) Perspectives on an intervention: what may work 3) Influences on uptake and successful weight control 4) Taking things forward. Phase Two: An intervention to facilitate the involvement of community midwives in supporting weight management for pregnant women living with obesity; a booklet about weight management in pregnancy; and a TPB scale were designed. Recommendations from midwives were integrated into the final intervention resource, and pilot testing of the scale led to refinement for use in phase 3. Phase Three: Midwives in the intervention group increased their intention to offer weight management support to pregnant women living with obesity. Furthermore, midwives in the intervention group increased actual weight management support for pregnant women living with obesity, after participating in the intervention. Conclusions: This study made a unique contribution to new knowledge by developing and testing a novel intervention that was underpinned by health psychology theory, which increased the intention and behaviour of community midwives to support pregnant women living with obesity, with managing their gestational weight gain.

Dans le but de prédire l’évolution d’un hypothétique accident au sein d’un réacteur nucléaire, nous nous proposons au travers de cette étude de comprendre la dynamique de bulles de gaz évoluant dans un bain stratifié constitué de deux liquides superposés. Pour ce faire, un dispositif expérimental muni de caméras à haute cadence a été construit afin d’observer en détail la dynamique de bulles d’air isolées et de trains de bulles traversant une interface séparant deux liquides newtoniens immiscibles initialement au repos. En faisant varier la taille des bulles injectées ainsi que les contrastes de viscosité entre les liquides d’un et quatre ordres de grandeur respectivement, ce dispositif a permis d’observer une grande variété de régimes d’écoulement. Dans certaines situations, les bulles de taille millimétrique restent piégées à l’interface liquide-liquide, tandis que les bulles plus grosses parviennent à traverser l’interface, entraînant une importante colonne de liquide lourd derrière elles. Après que l’influence des paramètres physiques a été qualitativement établie à la lumière de modèles simples, des simulations numériques de plusieurs situations sélectionnées ont été réalisées. Celles-ci ont été menées à partir de deux approches basées sur les équations de Navier-Stokes incompressibles, l’une utilisant une technique de capture d’interface, l’autre une description de type « interface diffuse » de Cahn-Hilliard. Les comparaisons entre les résultats expérimentaux et numériques ont confirmé la fiabilité des prédictions numériques dans la plupart des cas, mais ont également souligné le besoin d’améliorer la capture de phénomènes physiques à petite échelle, en particulier ceux liés au drainage de film. / In order to predict the evolution of a hypothetical accident in pressurized water nuclear reactors, this study aims to understand the dynamics of gas bubbles ascending in a stratified mixture made of two superimposed liquids. To this aim, an experimental device equipped with two high-speed video cameras was designed, allowing us to observe isolated air bubbles and bubble trains crossing a horizontal interface separating two Newtonian immiscible liquids initially at rest. The size of the bubbles and the viscosity contrast between the two liquids were varied by more than one and four orders of magnitude respectively, making it possible to observe a wide variety of flow regimes. In some situations, small millimetric bubbles remain trapped at the liquid-liquid interface, whereas larger bubbles succeed in crossing the interface and tow a significant column of lower fluid behind them. After the influence of the physical parameters was qualitatively established thanks to simple models, direct numerical simulations of several selected experimental situations were performed with two different approaches. These are both based on the incompressible Navier-Stokes equations, one making use of an interfacecapturing technique, the other of a diffuse Cahn-Hilliard description. Comparisons between experimental and numerical results confirmed the reliability of the computational approaches in most situations but also highlighted the need for improvements to capture small-scale physical phenomena especially those related to film drainage.