Detta examensarbete har utförts hos Vattenfall Eldistribution på avdelningen Kontroll och Skydd med målsättningen att utforma och utvärdera en nätmodell avsedd för jordslutningssimuleringar i PSCAD. Ombyggnationen från luftledningar till markkablar har medfört att kapacitansen i distributionsnätet ökat, vilket ställer högre krav på jordfelsutrustning och på nätanalyser för att kunna försäkra att en säkerställd frånkoppling kan ske enligt de myndighetskrav som föreligger. Syftet med arbetet har varit att undersöka hur en nätmodell bör utformas för analys av stationära in-svängningsförlopp och utvärdera hur stor noggrannhet som kan förväntas gentemot verkliga jordfelsprov vid felresistanser på främst 3 kΩ och 5 kΩ. Nätmodellen har ut-formats efter ett verkligt impedansjordat mellanspänningsnät med π-länkar i PSCAD och utifrån de nätuppgifter som förekommer i Vattenfalls näthanteringsprogram Netbas. Simuleringsresultaten har jämförts mot resultat från det verkliga nätets jord-felsprover vid olika inställningar på den centrala kompenseringsutrustningen som är placerad mellan den matande transformatorns nollpunkt och jord. Jordslutningssimuleringarna visar, trots antaganden och en viss osäkerhet omkring de verkliga nollföljdskomponenterna, godtyckliga simuleringsresultat vid avstämt och snedavstämt nät motsvarande ± 30 A gentemot ledningarnas kapacitiva strömmar vid en felresistans på 3 kΩ. Jordslutningssimuleringarnas händelseförlopp överensstäm-mer överlag väl mot det verkliga nätet samtidigt som jordslutningar vid 5 kΩ medför en större procentuell avvikelse. Särskilt framträdande avvikelser kunde urskiljas vid analys av fasvinkeln mellan nollföljdsspänning och nollföljdsström. En analys av nätmodellens resultat och troliga orsaker till uppkomna simulerings-avvikelser gentemot det verkliga nätet indikerar på att nätmodellens tillförlitlighet bör kunna optimeras ytterligare om noggrannare hänsyn tas gällande nollföljdsimpedanser, dc-komponenter och de toleranser som förekommer i det verkliga nätets avstäm-ningsutrustning och mätkretsar. / This thesis has been carried out at Vattenfall Eldistribution at the department Control and Protection with the objective to design and evaluate a network model for ground fault simulations in PSCAD. The reconversion from overhead lines to underground cables has led to increased capacitances in the distribution network and this places greater demands on the feeder protection unit and network analyzes in order to assure that faulted feeders are disconnected according to regulatory requirements. The aim of this work has been to determine how a network model could be designed for analysis of stationary signal characteristics and evaluate how great accuracy the power system model have compared to real earth fault test results. Earth fault simulations are performed with fault resistances of 3 kΩ and 5 kΩ. The power system model have been created to emulate a real impedance grounded network according to the π-model in PSCAD based on system information from Vattenfalls network management program Netbas. Results from the simulations have been compared against results obtained from real earth faults from the physical network with different settings on the central compensation equipment placed between the transformers neutral and ground. Simulations show, despite assumptions and some uncertainty about the actual zero sequence components similar results when fault resistance was 3 kΩ, both when compensation coil are fully tuned and out of tune ± 30 A corresponding to the feeder capacitance. The overall signal sequence conform quite well to the real network but at the same time simulations with 5 kΩ obtains greater deviations when results are represented in percentage. Particularly prominent abnormalities could be identified in the phase angle between zero sequence voltage and zero sequence current. An analysis of deviations from the simulations in the digital network model against the real system indicates that the model probably could be further optimized if zero sequence impedances, dc components, and tolerances that occur in the real systems reactive compensation equipment and measuring circuits are taken into account.

La topologie modulaire multiniveaux est une structure d'électronique de puissance construite par la mise en série de sous-modules identiques, composés chacun d'une cellule de commutation et d'un condensateur. Un tel système de conversion pouvant comporter un grand nombre de cellules permet d'augmenter le rendement global et la qualité des signaux en sortie. De plus, il permet d'utiliser des composants basse tension présentant un meilleur comportement dynamique et un rapport qualité-prix bien supérieur aux composants moyenne tension. Il permet également, par rapport aux structures conventionnelles, une grande souplesse pour la conception et la fabrication du fait de son aspect modulaire, tout en s'affranchissant d'un transformateur volumineux et onéreux en entrée. Comparé aux autres types de topologies, avantageuses avec un nombre limité de niveaux, le convertisseur modulaire multiniveaux semble être mieux adapté aux applications en moyenne et haute tensions, qui sont tributaires de l'association des composants de puissance. Néanmoins, pour la variation de vitesse, un certain nombre de défis technologiques ont été mis en évidence, compte tenu du fonctionnement particulier de l'onduleur modulaire multiniveaux et des contraintes imposées par l'opération en très basse fréquence. En le fonctionnement normal, la forme d'onde des courants internes, contrairement aux autres types de topologies, n'est pas symétrique en raison de la distribution du courant direct dans chaque bras. Cela entraîne une disparité significative en termes de dissipation thermique parmi les interrupteurs constituant un sous-module. Avec le choix d'une technologie de packaging 3D, la possibilité de refroidir les puces semi-conductrices en double-face offre une meilleure capacité de refroidissement et une nouvelle perspective de conception des modules pour cette application. Un nouveau concept de report de puces est présenté et un prototype de tel module a été réalisé, modélisé et caractérisé. Il permet d'équilibrer globalement la chaleur dissipée par les puces sur les deux faces du module, problème inhérent à l'emploi de structure 3D. Conjugué à la mutualisation d'un interrupteur par deux puces en parallèle, la nouvelle architecture a aussi pour objectif d'équilibrer le refroidissement double-face dans le temps. En effet, pour les opérations en basse fréquence, les interrupteurs fonctionnent en régime instationnaire avec de forte variation de température, il n'est donc plus possible de compenser les effets thermomécaniques de chaque composant l'un par l'autre, comme en régime stationnaire et avec un positionnement planaire des puces. D'autre part, d'un point de vu systémique, la stratégie de commande et le dimensionnement des condensateurs flottants de l'onduleur modulaire multiniveaux sont deux aspects intimement liés. En effet, les condensateurs flottants sont le siège d'ondulations de tension de très forte amplitude. Cela a pour effet de déstabiliser l'onduleur, voire de provoquer la destruction des composants en atteignant des niveaux de tension trop élevés. Ainsi, des contrôleurs judicieusement conçus permettent de réduire les ondulations indésirables, et a fortiori, d'embarquer des capacités moins importantes dans le système, tant que ces dernières sont inversement proportionnelles à l'ondulation de la tension. Afin d'avoir une compréhension approfondie sur les dynamiques régissant le convertisseur modulaire multiniveaux, un modèle dynamique global basé sur la représentation d'état a été établi. Bien que cette représentation soit limitée à l'harmonique 2 des grandeurs caractéristiques, elle permet une fidèle interprétation du mécanisme de conversion sans passer par des modèles énergétiques bien plus complexes à exploiter, et de proposer des lois de commande montrant leur efficacité notamment autour de la fréquence nominale. Cela a été vérifié sur une maquette de puissance réalisée dans le cadre de cette thèse. / Multilevel modular topology converts energy between two direct and alternative endings. This structure is constructed by the series connection of identical sub-modules, composed of a switching cell and a floating capacitor, and with arm inductors. Such a conversion system may reach a large number of levels increases the overall efficiency and quality of the output signals. In addition, it allows the use of low voltage components with better dynamics and cost effectiveness above the high voltage components. It also allows flexibility in the work of design and manufacture due to its modularity, while avoiding a bulky and expensive input transformer, regarding the conventional technology. Compared with other types of topologies, advantageous with a limited number of levels, the modular multilevel converter seems to be more suited for medium and high voltage applications, which are dependent on the association of power components. However, for variable speed drive application, a certain number of technological challenges have been highlighted, given the specific functional characteristics of the modular multilevel inverter and the constraints imposed by the very low frequency operation. On the one hand, for the normal operation of a multilevel modular converter, the waveform of the internal currents, in contrast to other types of topologies, is not symmetrical due to the distribution of the direct current in each phase leg. This may entail a significant disparity in terms of heat dissipation within the switching devices constituting a sub-module. Therefore, the problem of thermal management of active components is emphasized in the use of a modular multilevel converter. With the choice of a 3D packaging technology, interconnection by bumps, the ability to cool the semiconductor chips through the both sides of a module offers better cooling effects and a new perspective to design the power module for the studied structure. The concept of laying chips on both the two substrates of module without facing each other provides overall balanced dissipation in the space and permit to overcome the unbalanced heat distribution induced by bumps. Combined with the sharing of a switch by two chips in parallel, the proposal of the new architecture for 3D power module also aims to balance the double-sided cooling in the time range. Indeed, for the very low frequency operation, the switches operate in unsteady state where each switch has its own thermal behavior, it is no longer possible to compensate the thermo-mechanical constraints over each component with the help of the others, as in steady state and with a planar chips positioning scheme. On the other hand, from a systemic point of view, the control strategy and the dimensioning of floating capacitors of modular multilevel inverter are two interrelated aspects. Because the floating capacitors, having the role of energy sources, are loaded / unloaded through the modulation period, which causes very high voltage ripples across those capacitors with a very low frequency. This will destabilize the inverter and even provoke the destruction of components by approaching too high voltage levels. Thus, wisely designed controllers reduce unwanted ripples and, furthermore, allow embarking much smaller capacity in the system, as they are inversely proportional to the voltage ripple. In order to have a thorough understanding on the dynamics governing the modular multilevel converter, a comprehensive dynamic model based on state-space representation was established. Although this representation is limited to the second harmonic of characteristic variable, it allows a faithful interpretation of the conversion mechanism without using energy models, more complex to operate, and control laws can also be proposed and their effectiveness around the nominal frequency has been underlined. Concerning the very low frequency operations, another solution has been proposed and is ongoing patent pending.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-04-28T12:35:55Z No. of bitstreams: 1 karinalinomirandadeoliveira.pdf: 2833590 bytes, checksum: ce6010a8e780599c20721f9546fa946f (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-06-02T15:19:31Z (GMT) No. of bitstreams: 1 karinalinomirandadeoliveira.pdf: 2833590 bytes, checksum: ce6010a8e780599c20721f9546fa946f (MD5) / Made available in DSpace on 2016-06-02T15:19:32Z (GMT). No. of bitstreams: 1 karinalinomirandadeoliveira.pdf: 2833590 bytes, checksum: ce6010a8e780599c20721f9546fa946f (MD5) Previous issue date: 2016-03-10 / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / Dentre as diversas fontes de energia renovável, a energia eólica se destaca como uma das mais promissoras. Em meio ao cenário de crise energética em muitos países, crescimento da demanda, maior conscientização ambiental e maior exigência por uma energia de qualidade por parte das sociedades modernas, a energia eólica tem ganhado importância econômica e estratégica. No Brasil, os empreendimentos eólicos são contratados por meio de leilões através dos quais são declarados vencedores aqueles empreendimentos que ofertam o menor preço pela energia gerada. Este modelo vigente é responsável por acirrar a concorrência e, consequentemente, instigar a busca pela otimização das propostas. Considerando este aspecto, é de grande interesse o desenvolvimento de ferramentas computacionais que auxiliem profissionais a desenvolver projetos viáveis técnica e economicamente na fase de planejamento, e de preferência otimizados. Parques eólicos são compostos basicamente por aerogeradores, transformadores responsáveis por elevarem a tensão de saída das turbinas para níveis adequados de distribuição, cabos de média tensão e subestações. A construção da rede coletora de média tensão (rede interna), responsável pela interconexão de todos os aerogeradores e subestações, constitui parcela considerável dos custos globais, o que tem motivado diversos pesquisadores a publicar trabalhos que objetivam encontrar a melhor topologia da rede elétrica que, ao mesmo tempo, minimize os custos e respeite os critérios técnicos estabelecidos, tais como: radialidade, conectividade, variação da tensão nos barramentos, máxima condução de corrente pelo condutor (sobrecarga nos ramos), entre outras. Tendo em vista tais considerações, é proposto nesse trabalho um novo algoritmo de solução para otimização da rede coletora de média tensão de parques eólicos, englobando a determinação da topologia de conexão entre os aerogeradores e subestações e o dimensionamento dos condutores, baseado na utilização de um algoritmo genético modificado como método de otimização. Objetiva-se com esse método minimizar os custos com a aquisição de alguns equipamentos e com as perdas de energia ao longo de um horizonte de planejamento. O método proposto foi testado em parques eólicos fictícios e os resultados obtidos comprovam que o modelo elaborado pode ser utilizado para projetar uma arquitetura otimizada da rede de distribuição interna de parques eólicos. / Among the various sources of renewable energy, wind energy stands out as one of the most promising. Amid the energy crisis scenario in many countries, the demand growth, greater environmental awareness and greater demand for energy quality on the part of modern societies, wind energy has gained economic and strategic importance. In Brazil, wind projects are contracted by means of auctions through which are declared winners those projects that offer the lowest price for energy generated. This current model is responsible for increase competition and consequently instigate the search for optimization of the proposals. Considering this aspect, it is of great interest the development of computational tools to assist professionals to develop technical and economically viable projects in the planning stage, and preferably optimized. Wind farms are basically composed of wind turbines, transformers responsible for raise the output voltage of the turbines for adequate levels of distribution, medium voltage cables and substations. The construction of the medium voltage collector network (internal network), responsible for the interconnection of all wind turbines and substations, constitutes a considerable share of the overall costs, which has motivated many researchers to publish works that aim to find the best grid topology of the electrical network that, at the same time, minimizes costs and respects the technical criteria established, such as: radial configuration, connectivity, voltage variation in bus, current conduction maximum through the cable (overhead in the branches), among others. In view of these considerations, it is proposed in this paper a new solution algorithm to optimization of the medium voltage collector network of wind farms, comprising the determination of topology of connection between the turbines and substations and the sizing of conductors, based on the use of a modified genetic algorithm as optimization method. The objective of this methodology is to minimize the costs of acquisition of some equipment and energy losses over a planning horizon. The proposed method was tested on fictitious wind farms and the results show that the model developed can be used to design the optimized architecture of internal distribution network of wind farms.

The master´s thesis deals with the design of medium voltage power line protection and the calculation of reliability indicators. First, it deals with the possibilities of power system operation. Subsequently, it divides the networks according to the grounding of the transformer node and the switching elements and devices occurring in the MV distribution network are mentioned. It presents the basic classification of power line protection and its use, especially it focuses on overhead and cable MV power lines. It also discusses the reliability of the power supply and lists the basic reliability indicators and their possible calculation. The practical part describes the changes in the considered area of the distribution network, where the reconstruction of the power line VN872 and a new way of powering the village Drnholec will take place. The impact of this change on the reliability of the supplied energy is also calculated. Furthermore, the protection of the power line is designed and the correctness of its setting is then verified on the model in the PSS Sincal software.

Theses focuses on the evaluation of the possible means of active and reactive power control of generating units connected to medium voltage. First part summarizes analysis of Czech Republic medium voltage distribution grid. It summarizes means of autonomous and dispatcher control of generating units with respect to European Comission directive RfG, standard ČSN EN 50549-2 and national implementation PPDS. Following parts provide description of generating unit and distribution grid models used for simulation in PSCAD. Last part focuses on evaluation of results obtained via simulating steady-state scenarios as well as continuous simulation.

This thesis is focused on demonstrating the impact of the implementation of decentralized distributed energy sources (mainly RES) and electromobility technologies to electrical parameters in Czech medium voltage distribution network. Thesis is divided into two main chapters. First one is a brief theoretical summary of this problematic and the second one is a practical software simulation on a real medium voltage network. Proposed implementation scenarios are based on EU and national strategic plans for time period from 2020 to 2040.

This term project’s aim is to theoreticaly analyze thermal phenomena and losses in electrical power devices, describe the design and application of UniGear ZS1 type switchgear, put together a computer simulation model for thermal calculations of current and optimized solution and finally to discuss obtained results and compare them with experimentally acquired values. The main objective of this project is to determine, whether simulation is a viable and reliable enough method, that it could replace the costly real life physical testing. Modelling of the progress of thermal processes in different parts of the examined busbar will be done in computer aided design program Solidworks and its simulation plugin Flow Simulation.

Among the multilevel (ML)-voltage source converters (VSCs) for medium voltage (MV) and high power (HP) applications, the most used power topology is the three level (3L)-neutral point clamped (NPC)-VSC, due to its features such as common direct current (DC)-bus capability with medium point, absence of switches in series-connection, low part count, and straightforward control. The use of MV-insulated gate bipolar transistor (IGBT) modules as power switches offers further advantages like inexpensive gate drivers and survival capability after short-circuit. However, the IGBT modules have a reduced life cycle due to thermal stress generated by load cycles. Despite the advantages of the 3L-NPC-VSC, its main drawback is the uneven power loss distribution among its power devices. To address this issue and to improve other characteristics, more advanced ML converters have been developed. The 3L-active neutral point clamped (ANPC)-VSC allows an improved power loss distribution thanks to its additional IGBTs, which increase the number of feasible zero-states, but needs a loss balancing scheme to choose the proper redundant zero-state and a more complex commutation sequence between states. The 3L-neutral point piloted (NPP)-VSC improves the power loss distribution thanks to the use of series-connected switches between the output terminal and the positive and negative DC-link terminals. Other advanced power topologies with higher amount of levels include the 5L-ANPC-VSC, which has a flying capacitor per phase to generate the additional levels; and the 5L-stacked multicell converter (SMC), which needs two flying capacitors per phase. The goal of this work is to is to evaluate the performance of the aforementioned NPC-type ML converters with common DC-link, included the ones with flying capacitors, in terms of the power loss distribution and the junction temperature of the most stressed devices, which define, along with the nominal output voltage, the maximum power the converter can deliver. A second objective of this work is to describe the commutations of a MV 3L-ANPC-VSC phase leg prototype with IGBT modules, including all the intermediate switching states to generate the desired commutations.:Figures and Tables V Glossary XIII 1. Introduction 1 2. State of the art of medium voltage source converters and power semiconductors 5 2.1. Overview of medium voltage source converters 5 2.1.1. Multilevel Voltage Source Converter topologies 6 2.1.2. Application oriented basic characteristic of IGCTs and IGBTs 10 2.1.3. Market overview of ML-VSCs 11 2.2. IGBT modules for MV applications 12 2.2.1. Structure and Function 12 2.2.2. Electrical characteristics of the IGBT modules 15 2.2.3. Power losses and junction temperatures estimation 17 2.2.4. Packaging 19 2.2.5. Reliability and Life cycle of IGBT modules 21 2.2.6. Market Overview 23 2.3. Summary of Chapter 2 23 3. Structure, function and characteristics of NPC-based VSCs 25 3.1. The 3L-NPC-VSC 25 3.1.1. Power Topology 25 3.1.2. Switching states, current paths and blocking voltage distribution 26 3.1.3. Modulation of three-level inverters 28 3.1.4. Power loss distribution 32 3.1.5. “Short” and “long” commutation paths 33 3.2. The 3L-NPP-VSC 34 3.2.1. Power Topology 34 3.2.2. Switching states, current paths and blocking voltage distribution 35 3.2.3. Power Loss distribution 36 3.3. The 3L-ANPC-VSC 37 3.3.1. Power Topology 37 3.3.2. Switching states, current paths and blocking voltage distribution 38 3.3.3. Commutations and power loss distribution 39 3.3.4. Loss balancing schemes 57 3.4. The 5L-ANPC-VSC 60 3.4.1. Power Topology 60 3.4.2. Switching states, current paths and blocking voltage distribution 61 3.4.3. Commutation sequences 62 3.4.4. Power Loss distribution 70 3.4.5. Modulation and balancing strategies of capacitor voltages 70 3.5. The 5L-SMC 74 3.5.1. Power Topology 74 3.5.2. Switching states, current paths and blocking voltage distribution 75 3.5.3. Commutations and power loss distribution 78 3.5.4. Modulation and balancing strategies of capacitor voltages 80 3.6. Summary of Chapter 3 81 4. Comparative evaluation and performance of NPC-based converters 83 4.1. Motivation and goal of the comparisons 83 4.2. Basis of the comparison 83 4.2.1. Simulation scheme 85 4.2.2. Losses and thermal models for (4.5 kV, 1.2 kA) IGBT modules 86 4.2.3. Operating points, modulation, controllers and general parameters 88 4.2.4. Life cycle estimation 94 4.3. Simulation results of the 3.3 kV 3L-VSCs 97 4.3.1. Loss distribution and temperature at equal phase current 97 4.3.2. Maximum phase current 109 4.3.3. Life cycle 111 4.4. Simulation results of the 6.6 kV 5L and 3L-VSCs 115 4.4.1. Loss distribution and temperature at equal phase current 115 4.4.2. Maximum phase current 120 4.4.3. Life cycle 128 4.5. Summary of Chapter 4 132 5. Experimental investigation of the 3L-ANPC-VSC with IGBT modules 135 5.1. Goal of the work 135 5.2. Description of the 3L-ANPC-VSC test bench 136 5.2.1. Medium voltage stage 136 5.2.2. Gate drivers and digital signal handling 138 5.2.3. Measurement equipment 139 5.3. Double-pulse test and commutation sequences 140 5.3.1. Description of the double-pulse test for the 3L-ANPC-VSC 140 5.3.2. Commutation sequences for the double-pulse test 142 5.4. Commutation measurements 142 5.4.1. Switching and transition times 144 5.4.2. Type I commutations 145 5.4.3. Type I-U commutations 150 5.4.4. Type II commutations 150 5.4.5. Type III commutations 157 5.4.6. Comparison of the commutation times 157 5.4.7. Stray inductances of the “short” and “long” commutations 163 5.5. Summary of Chapter 5 167 6. Conclusions 169 Appendices 173 A. Thermal model of IGBT modules 175 A.1. General “Y” model 175 A.2. “Foster” thermal circuit 177 A.3. “Cauer” thermal circuit 178 A.4. From “Foster” to “Cauer” 179 A.5. Temperature comparison using “Foster” and “Cauer” networks 181 B. The “Rainflow” cycle counting algorithm 183 C. Description of the wind generator example 187 C.1. Simulation models 188 C.1.1. Wind turbine 188 C.1.2. Synchronous generator, grid and choke filter 189 C.1.3. Converters 189 C.2. Controllers 190 C.2.1. MPPT scheme 190 C.2.2. Pitch angle controller 191 C.2.3. Generator side VSC 192 C.2.4. Grid side VSC 193 D. 3D-surfaces of the maximum load currents in NPC-based converters 195 Bibliography 201 Bibliography 201 / Unter den Multilevel-Spannungsumrichtern für Mittelspannungs- und Hochleistungsanwendungen ist die am häufigsten verwendete Leistungstopologie der NPC-VSC, wegen seinen Merkmalen wie die Gleichstrom-Bus fähigkeit mit mittlerem Punkt, das Fehlen von Schaltern in Reihenschaltung, eine geringe Anzahl von Bauteilen und eine einfache Steuerung. Die Verwendung von Bipolartransistor Modulen mit isolierter Gate-Elektrode als Leistungsschalter bietet weitere Vorteile wie kostengünstige Gatetreiber und Überlebensfähigkeit nach einem Kurzschluss. Die IGBT-Module haben jedoch aufgrund der durch Lastzyklen erzeugten thermischen Belastung eine verkürzte Lebensdauer. Trotz der Vorteile des 3L-NPC-VSC ist der Hauptnachteil die ungleichmäßige Verteilung der Leistungsverluste zwischen den Leistungsgeräten. Um dieses Problem zu beheben und andere Eigenschaften zu verbessern, wurden fortgeschrittenere ML-Konverter entwickelt. Das 3L-ANPC-VSC ermöglicht dank seiner zusätzlichen IGBTs eine verbesserte Verlustleistungsverteilung, wodurch die Anzahl der möglichen Null-Zustände erhöht wird, es ist jedoch ein Verlustausgleichsschema erforderlich, um den richtigen redundanten Null-Zustand, und benötigt auszuwählende komplexere Kommutierungssequenz zwischen Zuständen. Das 3L-NPP-VSC verbessert die Verlustleistungsverteilung durch die Verwendung von in Reihe geschalteten Schaltern zwischen der Ausgangsklemme und den positiven und negativen Zwischenkreisklemmen. Andere fortgeschrittene Leistungstopologien mit einer höheren Anzahl von Stufen umfassen den 5L-ANPC-VSC, der pro Phase einen fliegenden Kondensator zur Erzeugung der zusätzlichen Stufen aufweist; und den 5L-SMC, der pro Phase zwei fliegende Kondensatoren benötigt. Das Ziel dieser Arbeit ist es, die Leistung der oben genannten NPC-VSC, einschließlich der mit fliegenden Kondensatoren, hinsichtlich der Verlustleistungsverteilung und der Sperrschichttemperatur der am stärksten beanspruchten Geräte zu bewerten. Diese definieren zusammen mit der Nennausgangsspannung die maximale Leistung, die der Umrichter liefern kann. Ein zweites Ziel dieser Arbeit ist die Beschreibung der Kommutierungen eines MV 3L-ANPC-VSC- Prototyps mit IGBT-Modulen einschließlich aller Zwischenschaltzustände, um die gewünschten Kommutierungen zu erzeugen.:Figures and Tables V Glossary XIII 1. Introduction 1 2. State of the art of medium voltage source converters and power semiconductors 5 2.1. Overview of medium voltage source converters 5 2.1.1. Multilevel Voltage Source Converter topologies 6 2.1.2. Application oriented basic characteristic of IGCTs and IGBTs 10 2.1.3. Market overview of ML-VSCs 11 2.2. IGBT modules for MV applications 12 2.2.1. Structure and Function 12 2.2.2. Electrical characteristics of the IGBT modules 15 2.2.3. Power losses and junction temperatures estimation 17 2.2.4. Packaging 19 2.2.5. Reliability and Life cycle of IGBT modules 21 2.2.6. Market Overview 23 2.3. Summary of Chapter 2 23 3. Structure, function and characteristics of NPC-based VSCs 25 3.1. The 3L-NPC-VSC 25 3.1.1. Power Topology 25 3.1.2. Switching states, current paths and blocking voltage distribution 26 3.1.3. Modulation of three-level inverters 28 3.1.4. Power loss distribution 32 3.1.5. “Short” and “long” commutation paths 33 3.2. The 3L-NPP-VSC 34 3.2.1. Power Topology 34 3.2.2. Switching states, current paths and blocking voltage distribution 35 3.2.3. Power Loss distribution 36 3.3. The 3L-ANPC-VSC 37 3.3.1. Power Topology 37 3.3.2. Switching states, current paths and blocking voltage distribution 38 3.3.3. Commutations and power loss distribution 39 3.3.4. Loss balancing schemes 57 3.4. The 5L-ANPC-VSC 60 3.4.1. Power Topology 60 3.4.2. Switching states, current paths and blocking voltage distribution 61 3.4.3. Commutation sequences 62 3.4.4. Power Loss distribution 70 3.4.5. Modulation and balancing strategies of capacitor voltages 70 3.5. The 5L-SMC 74 3.5.1. Power Topology 74 3.5.2. Switching states, current paths and blocking voltage distribution 75 3.5.3. Commutations and power loss distribution 78 3.5.4. Modulation and balancing strategies of capacitor voltages 80 3.6. Summary of Chapter 3 81 4. Comparative evaluation and performance of NPC-based converters 83 4.1. Motivation and goal of the comparisons 83 4.2. Basis of the comparison 83 4.2.1. Simulation scheme 85 4.2.2. Losses and thermal models for (4.5 kV, 1.2 kA) IGBT modules 86 4.2.3. Operating points, modulation, controllers and general parameters 88 4.2.4. Life cycle estimation 94 4.3. Simulation results of the 3.3 kV 3L-VSCs 97 4.3.1. Loss distribution and temperature at equal phase current 97 4.3.2. Maximum phase current 109 4.3.3. Life cycle 111 4.4. Simulation results of the 6.6 kV 5L and 3L-VSCs 115 4.4.1. Loss distribution and temperature at equal phase current 115 4.4.2. Maximum phase current 120 4.4.3. Life cycle 128 4.5. Summary of Chapter 4 132 5. Experimental investigation of the 3L-ANPC-VSC with IGBT modules 135 5.1. Goal of the work 135 5.2. Description of the 3L-ANPC-VSC test bench 136 5.2.1. Medium voltage stage 136 5.2.2. Gate drivers and digital signal handling 138 5.2.3. Measurement equipment 139 5.3. Double-pulse test and commutation sequences 140 5.3.1. Description of the double-pulse test for the 3L-ANPC-VSC 140 5.3.2. Commutation sequences for the double-pulse test 142 5.4. Commutation measurements 142 5.4.1. Switching and transition times 144 5.4.2. Type I commutations 145 5.4.3. Type I-U commutations 150 5.4.4. Type II commutations 150 5.4.5. Type III commutations 157 5.4.6. Comparison of the commutation times 157 5.4.7. Stray inductances of the “short” and “long” commutations 163 5.5. Summary of Chapter 5 167 6. Conclusions 169 Appendices 173 A. Thermal model of IGBT modules 175 A.1. General “Y” model 175 A.2. “Foster” thermal circuit 177 A.3. “Cauer” thermal circuit 178 A.4. From “Foster” to “Cauer” 179 A.5. Temperature comparison using “Foster” and “Cauer” networks 181 B. The “Rainflow” cycle counting algorithm 183 C. Description of the wind generator example 187 C.1. Simulation models 188 C.1.1. Wind turbine 188 C.1.2. Synchronous generator, grid and choke filter 189 C.1.3. Converters 189 C.2. Controllers 190 C.2.1. MPPT scheme 190 C.2.2. Pitch angle controller 191 C.2.3. Generator side VSC 192 C.2.4. Grid side VSC 193 D. 3D-surfaces of the maximum load currents in NPC-based converters 195 Bibliography 201 Bibliography 201

Energy security, global warming, and climate change have been a major source of global discussions and development. Likewise, the rising cost of electricity for consumers and exponential demand for energy are major factors driving the incremental growth and integration of sustainable forms of energy generation into power the system cycle. Distributed generation resources are majorly integrated into the electricity distribution system at the medium voltage (MV) and low voltage (LV) level of the utility grid system. Unexpected power outages on an electricity distribution network can lead to an islanding situation, in which a distributed generation system continues to supply power to the electricity grid. It is highly recommended by operational standards that, under such conditions, a distributed generation system is disconnected from the grid within a short period to prevent damage to power equipment and ensure personnel safety. The decoupling process requires an islanding detection method (IDM). Such detection methods are implemented in grid-tied power electronic converters (PEC) to detect and prevent islanding conditions.  The thesis investigates and describes an active islanding detection method, the active frequency drift with positive feedback. It also covers the parameter design and the analysis of the non–detection zone. The effectiveness of the method was verified through MATLAB/SIMULINK simulation

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