Since the end of the Current Wars in the 19th Century, alternating current (AC) has dominated the production, transmission, and use of electrical energy. The chief reason for this dominance was (and continues to be) that AC offers a way minimize transmission losses yet transmit large power from generation to load. With the Digital Revolution and the entrance of most of the post-industrialized world into the Information Age, energy usage levels have increased due to the proliferation of electrical and electronic devices in nearly all sectors of life. A stable electrical grid has become synonymous with a stable nation-state and a healthy populace. Large-scale blackouts around the world in the 20th and the early 21st Centuries highlighted the heavy reliance on power systems and because of that, governments and utilities have strived to improve reliability. Simultaneously occurring with the rise in energy usage is the mandate to cut the pollution by generation facilities and to mitigate the impact grid expansion has on environment as a whole. The traditional methods of transmission expansion are beginning to show their limits as utilities move generation facilities farther from load centers, which reduces geographic diversity, and the integration of nondispatchable, renewable energy sources upsets the current operating regime. A challenge faces engineers - how to expand generation, expand transmission capacity, and integrate renewable energy sources while maintaining maximum system efficiency and reliability. A technology that may prove beneficial to the operation of power system is high voltage direct current transmission. The technology brings its own set of advantages and disadvantages, which are in many ways the complement of AC. It is important to update transmission planning processes to account for the new possibilities that HVDC offers. This thesis submits a discussion of high voltage direct current transmission technology itself and an examination of how HVDC can be considered in the planning process. / Master of Science

Le transport d’énergie par des lignes HVDC constitue le principal réseau de transmission d’énergie électrique du futur. Les convertisseurs de puissance (par exemple de type MMC) qui constitueront ce réseau devront être capables de gérer des tensions de l’ordre de centaines de kilovolts ce qui rend critique l’alimentation des dispositifs de contrôle (gate-drive) de ces convertisseurs. Il est nécessaire de concevoir des solutions qui garantissent l’alimentation de ces gate-drives avec une isolation.Pour ce faire, un circuit basé sur le principe du flyback et utilisant un JFET normalement passant a été développé. Il est placé en parallèle d’un condensateur typiquement connecté aux bornes d’un bras d’onduleur. Il permet d’alimenter le dispositif de puissance dès qu’une faible tension est appliquée à son entrée. Cette fonction est assurée grâce au caractère normalement passant du JFET. Pour le prototype développé, la tension du bras est de 2 kV. La tension de sortie est régulée à 24 V. De nos jours, des JFET normalement passants avec une tenue en tension supérieure à 2 kV n’existent pas sur le marché. Donc, pour supporter les tensions mises en jeu dans le circuit, une mise en série de JFET SiC normalement passants commandés par un MOSFET Si a été réalisée (montage « super-cascode »). Le circuit développé est capable de fournir 20 W pour alimenter des gate-drives à des potentiels flottants. Le rendement obtenu est proche de 60 %. Aussi, le problème d’isolation est résolu par cette solution d’auto-alimentation. / HVDC power transmission is the future of the electrical energy transmission network. The power converters (e.g. MMC) used in this network will be able to cope with voltages of hundreds of kV, making the power supply of the gate-drive devices in these converters challenging. It is then necessary to design solutions that guarantee the power supply of these gate-drives, while providing high voltage isolation. To do this, a circuit, based on the flyback principle, was developed. It is placed in parallel with a capacitor typically connected to a half-bridge circuit. It has an auto-start feature. This allows to supply the gate-drive as soon as a low voltage is applied to the input of the self-supply system. This is obtained by taking advantage of the normally-ON character of the JFET. In our prototype, the input voltage is 2 kV. High voltage JFETs of 2 kV and higher breakdown voltages are not yet available on the market. So, to achieve this high voltage capacity, a series of Normally-ON SiC JFETs controlled by a low voltage Si MOSFET (Super-cascode circuit) is used in the circuit. The developed circuit is able to supply 20 W at different floating potentials with output voltage regulated at 24 V and an efficiency close to 60%. The isolation problem is then solved using this solution.

Ce mémoire présente le travail de thèse réalisé auprès des laboratoires LAPLACE et SATIE ainsi que les services EDYNE3 et EDYYLIC d'AIRBUS OPERATIONS. Le sujet porte sur les problèmes CEM apparaissant dans les convertisseurs de puissance embarqués à bord des futurs avions plus électriques. Le manuscrit est composé de cinq parties. La première partie, d'introduction, traite de la problématique CEM avion, la deuxième de la modélisation des éléments de la chaine de conversion DC/AC étudiée. Le troisième est composé d'une étude comparative par simulation des différentes solutions. La quatrième partie traite de la réalisation de la solution choisie et enfin le cinquième et dernier chapitre de l'étude expérimentale de celle-ci. / The studies conducted during this thesis deals with conducted EMC problems of an inverter associated to its actuator. Accurate high frequency models of every element of the DC/AC converter and actuator have been realised from measures. Then a comparative study of different topologies of converters have been led from simulations in order to determine the best solution minimising EMC current. The selected inverter was realised and the experimental results were compared to simulations validating them. Finally, a comparison of EMC filters architecture led to choose a better solution in order to avoid the increasing of mass.

Cette thèse s’intéresse au problème de la qualité de l’énergie électrique sous l’angle particulier des harmoniques, leurs sources, leurs effets et les solutions permettant de les réduire. Deux solutions sont principalement considérées, les convertisseurs à indice de pulsation élevé et les filtres actifs. Ce travail a été mené en faisant porter l’accent sur le réseau électrique thaïlandais. C’est ainsi qu’une présentation de l’évolution de la façon dont l’électricité est produite, transportée et distribuée en Thaïlande est effectuée avant de décrire les contraintes imposées sur les harmoniques. Les différents systèmes de liaison à courant continu haute tension (CCHT) actuellement installés dans le monde sont rappelés avant de décrire en détails les différents composants et le contrôle de la liaison 300-600 MW existant entre la Thaïlande et la Malaisie. Après avoir ensuite présenté les différentes solutions envisageables de réduction des harmoniques, un exemple de réalisation, l’une des premières en Thaïlande utilisant un contrôle numérique, est détaillé afin d’illustrer les avantages de ce type de solution. La thèse se termine sur la présentation d’une méthode originale de modélisation des convertisseurs à indice de pulsation élevé. Cette modélisation repose sur une solution analytique exacte du problème d’état qui est considéré sur le plus petit intervalle permettant, en utilisant des propriétés de symétrie, de reconstruire la période de fonctionnement du dispositif. Le modèle ainsi développé donne des informations sur le fonctionnement du système tant dans les domaines fréquentiel que temporel / The problem of quality of electrical energy is the main object of this thesis. This problem is considered especially from the point of view of harmonics, sources, effects and solutions to reduce them. Two main solutions are considered, multi-pulse converters and active filters. This work is developed with a particular emphasis on the Thai electrical network. Then, the production, transmission and distribution system of electricity in Thailand and the harmonics regulations are presented. The different types of HVDC interconnection systems which are installed in the world today are detailed before presenting the 300/600 MW Thailand-Malaysia HVDC interconnection. After presenting the different possible solutions to avoid harmonics, a realized example, one of the first one developed in Thailand with a numerical control, is detailed to show the advantages of such a solution. The thesis ends on the presentation of an original modelling method of multi-pulse converters. The model is based on an exact analytical solution of the state problem which is considered on the smallest interval, which can, by using property of symmetry, rebuild the whole period. The result model gives the full information on the operation of the whole device both in time and frequency domains

A new concept, the multi level voltage/current reinjection ac/dc conversion, is described in this thesis. Novel voltage and current source converter configurations, based on voltage and current reinjection concepts are proposed. These converter configurations are thoroughly analyzed in their ac and dc system sides. The fundamentals of the reinjection concept is discussed briefly, which lead to the derivation of the ideal reinjection waveform for complete harmonic cancellation and approximations for practical implementation. The concept of multi level voltage reinjection VSC is demonstrated through two types of configurations, based on standard 12-pulse parallel and series connected VSC modified with reinjection bridges and transformers. Firing control strategies and steady state waveform analysis are presented and verified by EMTDC simulations. The multi level current reinjection CSC is also described using two configurations based on standard 12-pulse parallel and series connected CSC modified with associated reinjection circuitry. Firing control strategies and steady state waveform analysis are presented and verified by EMTDC simulations. Taking the advantage of zero current switching in the main bridge valves, achieved through multi level current reinjection, an advanced multi level current reinjection scheme, consisting thyristor main bridges and self-commutated reinjection circuitry is proposed. This hybrid scheme effectively incorporates self-commutated capability into a conventional thyristor converter. The ability of the main bridge valves to commutate without the assistance of a turn-off pulse or line commutating voltage under the zero current condition is explained and verified by EMTDC simulations. Finally, the applications of the MLCR-CSC are discussed in terms of a back to back HVDC link and a long distance HVDC transmission system. The power and control structures and closed loop control strategies are presented. Dynamic simulation is carried out on PSCAD/EMTDC to demonstrate the two systems ability to respond to varying active and reactive power operating conditions.

L'intégration des liaisons à courant continu dans les systèmes électriques permet d'accroitre les possibilités de pilotage des réseaux, ce qui permet d'en améliorer la sûreté et de raccorder de nouveaux moyens de production. Pour cela la technologie VSC-HVDC est de plus en plus plébiscitée pour interconnecter des réseaux non synchrones, raccorder des parcs éoliens offshore, ou contrôler le flux d'énergie notamment sur des longues distances au travers de liaisons sous-marines (liaison NorNed). Les travaux de cette thèse portent sur la modélisation, la commande non-linéaire et la stabilisation des systèmes VSC-HVDC, avec deux axes de travail. Le premier se focalise sur la conception et la synthèse des lois de commandes non-linéaires avancées basées sur des systèmes de structures variables (VSS). Ainsi, les commandes par modes glissants (SMC) et le suivi asymptotique de trajectoire des sorties (AOT) ont été proposées afin d'assurer un degré désiré de stabilité en utilisant des fonctions de Lyapunov convenables. Ensuite, la robustesse de ces commandes face à des perturbations et/ou incertitudes paramétriques a été étudiée. Le compromis nécessaire entre la robustesse et le comportement dynamique requis dépend du choix approprié des gains. Ces approches robustes, qui sont facile à mettre en œuvre, ont été appliquées avec succès afin d'atteindre des performances dynamiques élevées et un niveau raisonnable de stabilité vis-à-vis des diverses conditions anormales de fonctionnement, pour des longueurs différentes de liaison DC. Le deuxième vise à étudier l'influence de la commande du convertisseur VSC-HVDC sur l'amélioration de la performance dynamique du réseau de courant alternatif en cas d'oscillations. Après une modélisation analytique d'un système de référence constitué d'un groupe connecté à un convertisseur VSC-HVDC via un transformateur et une ligne, un contrôleur conventionnel simple PI est appliqué au niveau du convertisseur du système pour agir sur les oscillations rotoriques de la machine synchrone. Cette commande classique garantie une amélioration acceptable des performances dynamiques du système; surtout pour l'amortissement des oscillations de l'angle de puissance de la machine synchrone lors de défauts.

Τα τελευταία χρόνια έχει αρχίσει να διαδίδεται με γρήγορους ρυθμούς η μέθοδος μεταφοράς ισχύος μέσω συνεχούς ρεύματος. Προς αυτή την κατεύθυνση ώθηση έδωσε η ανάπτυξη νέων ημιαγωγικών διακοπτικών στοιχείων οδηγώντας σε περεταίρω ανάπτυξη και χρήση των συστημάτων μεταφοράς με συνεχές ρεύμα. Σε αυτή τη διπλωματική εργασία μελετάται ένα σύστημα μεταφοράς ισχύος με διασύνδεση συνεχούς ρεύματος (HVDC), που συνδέεται ανάμεσα σε δυο εναλλασσόμενα ηλεκτρικά δίκτυα με και χωρίς φορτίο. Την διασύνδεση συνεχούς ρέματος πραγματοποιούν δυο back-to-back AC/DC μετατροπείς VSC, που αναλαμβάνουν τους ρόλους του ανορθωτή και του αντίστροφα ισχύος. Οι μετατροπείς χρησιμοποιούν την διαμόρφωση πλάτους παλμού PWM. Αρχικά μελετάται θεωρητικά το μοντέλο των μετατροπέων και του back-to-back HVDC συστήματος και στην συνέχεια σχεδιάζεται και αναλύεται η λειτουργία του ανάμεσα σε δυο δίκτυα εναλλασσομένου ρεύματος με ή χωρίς την ταυτόχρονη παρουσία φορτίου. Τέλος προσομοιώνεται το σύστημα μέσω του λογισμικού Matlab και συγκεκριμένα της εφαρμογής Simulink για την εξαγωγή συμπερασμάτων. / In the past few years the method of power transmission by means of direct current has expanded rapidly. To this direction a push forward has been given by the development of new semi-conductive switching valves leading to a further development of transmission systems by direct current. In this thesis what is considered is a power transmission system via direct current HVDC connected between two AC electric networks with or without load. The direct current connection is achieved through back-to-back AC/DC converters VSC which undertake the role of rectifier and that of inverter of power. The converters use the Pulse Width Modulation (PWM). At first the converter model and the back-to-back HVDC system is theoretically approached and in the process what is designed and analyzed is its function between two networks of AC current with or without the simultaneous presence of load. Finally the system is simulated through software Matlab and specifically the application of simulink in order to draw conclusions.

In this thesis, an evaluation of the existing control system for ABB: s HVDC Classic Links is performed in order to investigate whether a possible improvement to commutation failure prediction is possible and to be recommended. The thesis starts with a theoretical approach to the complexity of consequences of increasing the extinction angle (γ) in order to prevent commutation failure in inverter operation, which is later confirmed through using the simulation software PSCAD to evaluate coherence between simulation results and theory. Dynamic power studies are performed through simulations in the electromagnetic time domain transient tool PSCAD in order to establish a possible improvement to the existing commutation failure prediction today used in ABB control systems for HVDC applications.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The worldwide increase in the popularity of high voltage direct current (HVDC) power transmission application has led to questions regarding the performance of high voltage alternating current (HVAC) insulators when energized under HVDC excitation. These questions have led researchers conduct numerous research projects worldwide. A particular question NamPower (the power utility in Namibia) has faced is: how do these insulators perform and age when energized under HVDC excitation in heavily polluted environments? This question was only partly answered by some insulator ageing tests conducted under laboratory conditions for HVDC excitation. However, the natural ageing tests on insulators, which are preferred, have to date been confined predominantly to HVAC excitation voltages. Thus, this research was initiated to investigate the natural ageing performance of insulators under both HVAC and HVDC excitations, when subjected to harsh marine pollution environments. This research project involved performance and ageing tests on three identical sets of line insulators made from different insulator materials, energised under HVAC and both polarities HVDC excitations respectively. The tests were conducted at Koeberg insulator pollution test station (KIPTS), which is a natural marine pollution insulator test station located near Cape Town, along the west coast of South Africa, approximately 50 m from the sea. The set of insulators consisted of EPDM silicone alloy rubber, HTV silicone rubber, RTV silicone rubber coated porcelain, Porcelain and Glass insulators. The HVAC excitation voltage was chosen as 12.7 kV r.m.s. phase-to-ground and it was decided to use a HVDC excitation voltage equal to this value. The research results showed that the insulators made from HTV silicone rubber performed better than the insulators made from EPDM silicone alloy rubber under all excitation voltages. It is also showed that RTV silicone rubber coated porcelain insulators performed better than Glass and Porcelain insulators under all excitation voltages. / AFRIKAANSE OPSOMMING: Die wêreld wye toename in gewildheid van hoë spanning gelyk stroom (HSGS) krag transmisie aplikasie het gelei na vrae oor die effektieweteit van hoë spanning wissel stroom (HSWS) insolators in HSGS aplikasies. Hierdie vrae het gelei na baie navorsings projekte. Een vraag waarmee NamPower (die krag voorsienings maatskapy in Namibia) gekonfronteer was, was hoe gaan die insolators wat onderworpe is aan ’n HSGS toevoer reageer in ’n baie besoedelde omgewing. Hierdie vraag was slegs gedeeltelik beantwoord deur verouderings toetse op insolators wat gedoen is in ’n labaratorium met ’n HSGS toevoer. Inteendeel, die meeste natuurlike verouderings toetse op insolators, soos verkies, is meestal gedoen met ’n HSWS toevoer. Om hierdie rede was hierdie navorsing begin om natuurlike verouderings toetse te doen op insolators onderworpe beide aan HSWS en HSGS toevoere binne ’n marien besoedelde omgewing. Hierdie navorsings projek gaan oor prestering en verouderings toetse op drie, identiese, transmissie lyn insolator stelle, wat onderskeidelik onderworpe was aan HSWS en beide polariteite HSGS toevoere. Die toetse was gedoen by Koeberg insolator besoedeling toets stasie (KIBTS) wat naby Kaapstad geleë is langs die weskus van Suid Africa omtrent 50 m van die see. ’n Stel toets insolators bestaan uit EPDM silikon allooi rubber, HTV silikon rubber, RTV silikon rubber bedekte porselein, Porselein en Glas insolators. Die HSWS waarde waarmee die insolators getoets was, was 12.7 kV w.g.k., fase-na-grond, en dit was besluit om ’n HSGS waarde gelyk aan hierdie spannings waarde te gebruik. Die navorsings resultate wys dat insolators wat gemaak is met HTV silikon rubber presteer beter as insolators wat met EPDM silikon allooi rubber gemaak is onder al die verskillende toevoere. Dit wys ook dat RTV silikon rubber bedekte porselein presteer beter as Porselein en Glas insolators onder al die verskillende toevoere.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This PhD thesis discusses the use of the power plant capacity in HVDC transmission systems during inactive periods of the main converters to feed local loads, aiming at a better AC power quality and DC transmission. The power available in the inactive periods is drained by an auxiliary converter connected in parallel with the HVDC converter. This energy can be used to: feed thermal equipments; battery charging; supply of local services; AC power re-injection; and to produce high purity hydrogen and oxygen through electrolysis. The overall control was designed to improve the power transmission quality at the AC side of the HVDC plant. Simulated and lab practical results from a reduced model of a HVDC plant and from the auxiliary converter connected in parallel with the main converter are presented. The proposed arrangement of converters demonstrates the possibility of THD reduction and increase of the power and utilization factors, without disturbing the efficiency of the HVDC transmission system, and making evident loss reduction, sizing of the harmonic filters and PF reactors. For their special characteristics, at the end of this thesis it is presented the state of art of the auxiliary converter energy utilization to produce hydrogen and oxygen through water electrolysis. / Esta tese discute o uso da capacidade instalada dos sistemas de transmissão CCAT nos períodos inativos das chaves eletrônicas dos conversores de potência para alimentar cargas locais, de tal modo que a qualidade da energia e a transmissão em corrente contínua possam ser amplamente melhoradas. A energia dos períodos inativos é drenada por um conversor auxiliar conectado em paralelo com o conversor CCAT. Esta energia pode servir para: alimentar equipamentos térmicos; carregar baterias; suprir serviços ancilares; retro-injeção na rede; e produção de hidrogênio e oxigênio por eletrólise com alto grau de pureza, entre outras cargas. O controle dos conversores conectados em paralelo foi projetado criteriosamente visando melhorar a qualidade da energia no lado CA da planta de CCAT. São apresentados dados provenientes da adição do conversor auxiliar em paralelo com o conversor CCAT, tanto de simulações como de dados reais e ensaios de laboratório em um protótipo em escala reduzida. Com o arranjo de conversores proposto nesta tese fica demonstrada a possibilidade de uma redução considerável da distorção harmônica total e o aumento dos fatores de potência e de utilização, sem prejudicar o rendimento da transmissão CCAT. Também fica evidente a redução de perdas e do tamanho dos filtros harmônicos e reatores de compensação de reativos por diminuir a corrente nos mesmos. Pela sua peculiaridade, no final desta tese é apresentado um estudo sobre o estado da arte da utilização da energia processada por conversores auxiliares junto a conversores CCAT para a produção de hidrogênio e oxigênio através da eletrólise de água.