In recent years, photovoltaic (PV) power production have seen an increase and the PV power systems are often located in the distribution grids close to the consumers. Since the distributions grids rarely are designed for power production, investigation of its effects is needed. It is seen in this thesis that PV power production will cause voltages to rise, potentially to levels exceeding the limits that grid owners have to abide by. A model of a distribution grid is developed in MathWorks MATLAB. The model contains a transformer, cables, households, energy storage systems (ESS:s) and photovoltaic power systems. The system is simulated by implementing a numerical Forward Backward Sweep Method, solving for powers, currents and voltages in the grid. PV power systems are added in different configurations along with different configurations of ESS:s. The results are analysed, primarily concerning voltages and voltage limits. It is concluded that addition of PV power production in the distribution grid affects voltages, more or less depending on where in the grid the systems are placed and what peak power they have. It is also concluded that having energy storage systems in the grid, changing the power factor of the inverter for the PV systems or lowering the transformer secondary-side voltage can bring the voltages down. / På senare tid har det skett en ökning i antalet solcellsanläggningar som installeras i elnätet och dessa är ofta placerade i distributionsnäten nära hushållen. Eftersom distributionsnäten sällan är dimensionerade för produktion så behöver man utreda effekten av det. I det här arbetet visas det att solcellsproduktion kommer att öka spänningen i elnätet, potentiellt så mycket att de gränser elnätsägarna måste hålla nätet inom överstigs. En modell över lågspänningsnätet skapas i MathWorks MATLAB. Modellen innehåller transformator, kablar, hushåll, energilager och solcellsanläggningar. Systemet simuleras med hjälp av en numerisk Forward Backward Sweep-lösare som beräknar effekter, strömmar och spänningar i elnätet. Solcellanläggningarna placeras ut i elnätet i olika konfigurationer tillsammans med olika konfigurationer av energilager. Resultaten från simuleringarna analyseras främst med avseende på spänningen i elnätet utifrån dess gränser. De slutsatser som dras i arbetet är att solcellsproduktion kommer att påverka spänningen, mycket beroende på var i elnätet anläggningarna placeras och storleken hos dem. Det visas också att energilager, justering av effektfaktor hos solcellsanläggningarna eller en spänningssänkning på transformatorns lågspänningssida kan få ner spänningen i elnätet. / <p>LiTH-ISY-EX--19/5194--SE</p>

Le domaine aéronautique connait de nos jours un engouement sans précédent autour de l’avion plus électrique. L’importance du nombre d’équipements électriques est à un tel point que l’amélioration de leur fiabilité devient incontournable. Actuellement, les composants passifs occupent 75 % des éléments électroniques utilisés en avionique dont la moitié correspond à des condensateurs. Ces derniers doivent donc répondre aux exigences environnementales avioniques assez contraignantes. C’est dans ce contexte que nous nous sommes intéressés particulièrement à l’étude des condensateurs à technologie film utilisant le polypropylène ou le polyester comme diélectrique. Afin de mieux comprendre le comportement fréquentiel de cette technologie, deux modèles fins de condensateurs films ont été développés, permettant ainsi de suivre les évolutions de leurs grandeurs électriques dans des conditions cohérentes avec l’application. Dans un deuxième temps, l’effet des contraintes en tension et en température constantes a été étudié sous la forme de facteurs d’accélération du vieillissement. Cela a été établi par l’intermédiaire de plusieurs essais, permettant d’établir les lois d’évolutions temporelles des paramètres électriques des condensateurs. Comme ces contraintes constantes ne sont pas toujours représentatives des conditions réelles d’utilisation, les cinétiques de dégradation ont été comparées à celles où les condensateurs sont sollicités par de fortes ondulations de courant, seules ou associées à une tension continue. Enfin, la dernière partie de notre travail expose l’utilisation des données expérimentales issues des essais de vieillissement dans un objectif de diagnostic en ligne. Les techniques utilisées assurent l'analyse de la dégradation de ces composants, étape essentielle dans la prédiction de l’état de santé des condensateurs en ligne / Nowadays, aeronautic research field is moving towards a more electric aircraft. Although this evolutionary path offers many advantages from a financial and ecological point of view, the increased power source usage sets additional constraints on the different electrical systems used onboard. Currently, passive components occupy 75% of the overall electronic equipments used in avionics, whose 50% corresponds to capacitors. Consequently, these latter must be able to withstand the harsh avionic operating conditions. In this thesis we were particularly interested in the study of metallized film capacitors technology using polyester or polypropylene as dielectric. A first approach consisted on the modeling of these components as function of frequency in order to study the evolution of their electrical parameters under consistent avionic stresses. These models were also developed on the purpose of tracking the degradation of the capacitors parameters over time. This operation was done by the means of accelerated floating ageing tests, where capacitors were subjected to different constant voltages and temperatures. Original capacitance ageing laws were thus proposed based on the identification of voltage and temperature degradation kinetics. However, since traditional floating ageing tests, do not reflects the normal ageing of the component, degradation kinetics of metallized films capacitors under high ripple currents, alone or combined with a DC voltage across the devices terminals where also studied, and the associated failure mechanisms were identified. A final step consisted on the health monitoring of metallized film capacitors online based on the experimental ageing data

Dans le domaine aéronautique, l'optimisation du rendement énergétique global, la réduction des masses embarquées et la nécessité de répondre aux besoins énergétiques croissants conduisent à développer de nouvelles technologies et méthodes pour générer l'énergie électrique à bord, pour la distribuer, la convertir et la stocker. Dans cette thèse, des éléments de stockage de l'énergie électrique sont caractérisés dans l'optique d'être modélisés. Parmi les différents systèmes de stockage, présentés dans un état de l'art préliminaire, sont retenus les supercondensateurs et les accumulateurs électrochimiques Lithium-ion polymère, considérés respectivement comme des sources de puissance et d'énergie, à l'échelle de l'application. Ces moyens de stockage sont caractérisés par chronopotentiométrie à courant constant et par spectrométrie d'impédance électrochimique. Les essais sont éffectués dans des conditions expérimentales, définissant le domaine de validités des modèles, en cohérence avec les contraintes de l'application finale. Différents modèles sont alors développés en fonction de leur utilisation : des modèles simples, fonctionnels et suffisants pour la gestion globale d'énergie et des modèles dynamiques, comportementaux et nécessaires pour l'analyse de la qualité du réseau. Ils sont ensuite validés sur des profils de mission. Pour disposer d'un système de stockage performant et en adéquation avec les besoins énergétiques de l'aéronef, une méthode de dimensionnement est proposée, associant des composants de stockage complémentaires. Un gestion fréquentielle des sources est mise en oeuvre de manière à minimiser la masse du système de stockage. / In aeronautics, the optimization of the global energetic efficiency, the reduction of the embedded weight and the need to meet the growing energetic requirements lead to develop new technologies and methods to generate electrical energy, to distribute it, to convert it and to store it aboard. In this thesis, electrical energy storage systems are characterized with a view to be modeled. Among varied storage systems, presented in an introductory state of the art, ultracapacitors and Lithium-ion polymer secondary batteries are studied. These components are considered respectively as power and energy sources, in regards to the application scale. These storage systems are characterized by chronopotentiometry at constant current and by electrochemical impedance spectrometry. Tests are carried out in experimental conditions which define the validity area of modeling, in relation with the application constraints. Different models are developed according to their future use : simple models, which are functional and sufficient for the global energy management, and dynamics models, which are behavioral and necessary for the analysis of the network quality. Then, they validated thanks to mission profiles. Finally, to dispose of an efficient storage system that meets the energetic requirements of the aircraft, a sizing method is suggested by combining complementary storage systems. An energy management based on frequency approach is implemented in order to minimize the storage system weight.

[pt] O planejamento da expansão da transmissão (PET) visa identificar novos reforços para a rede, permitindo uma conexão tecnicamente adequada entre demanda e geração de energia elétrica, ambas previstas para um determinado horizonte de planejamento. Um bom plano de expansão deve garantir o equilíbrio entre os custos de investimento e operação, mantendo um nível satisfatório de segurança no fornecimento de energia elétrica. Entretanto, a identificação de bons planos de expansão para o PET tem se tornado uma tarefa cada vez mais difícil. Isso se deve, principalmente, às características e dimensões dos sistemas atuais, a não linearidade e natureza combinatória do problema de otimização e às incertezas presentes nos dados. Os erros de previsão, a indisponibilidade de equipamentos e a disponibilidade dos recursos naturais são parâmetros que variam de forma aleatória e inserem um alto grau de incerteza nos sistemas elétricos, o qual aumenta proporcionalmente com o horizonte de planejamento. Uma das incertezas mais relevantes a ser gerenciada nas próximas décadas será a capacidade de geração oriunda de fontes renováveis, em particular as eólicas, devido à sua grande variabilidade. A utilização de dispositivos de armazenamento permitirá melhor aproveitamento dessas fontes e, portanto, torna-se necessário o desenvolvimento de ferramentas computacionais capazes de considerar tais dispositivos no problema PET. Esta dissertação apresenta uma nova metodologia de apoio ao problema PET inserindo armazenadores de energia elétrica para aumentar o aproveitamento de fontes renováveis no sistema. Isso, respeitando as restrições de segurança da rede, acompanhando à curva de demanda e levando em consideração as variáveis operativas destes dispositivos. A possibilidade de incluir sistemas de armazenamento de energia elétrica é avaliada através de uma análise custo-benefício. A metodologia proposta é aplicada a um sistema teste, submetido a diversas condições operativas, e os resultados obtidos são amplamente discutidos. / [en] The transmission expansion planning (TEP) aims at identifying new reinforcements for the network, allowing a technically adequate connection between demand and generation of electric energy, both foreseen for a given planning horizon. A good expansion plan must ensure a balance between investment and operating costs, while maintaining a satisfactory level of security of the electric energy supply. However, identifying good expansion plans for TEP has become an increasingly difficult task. This is mainly due to the characteristics and dimensions of the current systems, the nonlinearity and combinatorial nature of the optimization problem, and the uncertainties present in the data. Forecasting errors, equipment unavailability, and the availability of natural resources are parameters that vary in a random way and insert a high degree of uncertainty in the electrical system, which proportionally increases with the planning horizon. One of the most relevant uncertainties to be managed in the upcoming decades will be the generation capacity from renewable sources, particularly wind power, due to its great variability. Storage devices will allow better use of these sources and, therefore, it becomes necessary to develop computational tools capable of considering such devices in the TEP problem. This dissertation presents a new methodology to support the TEP problem by inserting electric energy storage to increase the use of renewable energy in the system, while respecting the security restrictions of the network, following the demand curve and taking into account the operational variables of these devices. The possibility of including electric energy storage systems is evaluated through a costbenefit analysis. The proposed methodology is applied to a test system, subject to various operating conditions, and the obtained results are widely discussed.

Small signal oscillation has been always a major concern in the operation of power systems. In a generator, the electromechanical coupling between the rotor and the rest of the system causes it to behave in a manner similar to a spring mass damper system. Following any disturbance, such as sudden change in loads, actuations in the output of turbine and faults etc. it exhibits an oscillatory behaviour around the equilibrium state. The use of fast acting high gain AVRs and evolution of large interconnected power systems with transfer of bulk power across weak transmission links have further aggravated the problem of these low frequency oscillations. Small oscillations in the range of about 0.1Hz to 3.5Hz can persist for long periods, limiting the power transfer capability of the transmission lines. These oscillations can be reduced by incorporating auxiliary controllers on generator excitation system. Power System Stabilizers (PSSs) were developed to produce additional damping by modulating the generator excitation voltage. Designing effective PSS for all operating conditions especially in large interconnected power systems still remains a difficult and challenging task. More and more power electronic based controllers have been and will be used in power systems. Many of these controllers such as Static Var Compensators (SVCs), Static Synchronous Compensators (STATCOMs) and Unified Power Flow Controllers (UPFCs) etc., are incorporated in power transmission networks to improve its operational capability. In addition, some of the energy storage systems such as Battery Energy Storage systems (BESS), Super conducting Magnetic Energy Storage System (SMES) as well large non-conventional energy sources are also increasingly being integrated with the power grid. With large integration of these devices, there is a significant impact on system stability, more importantly on small signal oscillatory instability of the power system. This thesis primarily focuses on impact of such devices on small signal oscillatory stability of the power systems. More specifically in this thesis small signal stability analysis of a Single Machine Infinite Bus (SMIB) system with a grid connected wind powered Permanent Magnet Synchronous Generator (PMSG) has been presented. A SMIB system has been purposely chosen so that general conclusions can be obtained on the behaviour of the embedded STATCOM/Energy Source (ES) system on system stability. With a better understanding of the impact of such a system it would be probably possible to analyze more complicated multimachine power system and their impact on system stability. Small signal model of the complete system which comprises the generator, transmission network, inter connecting STATCOM, the wind power generator and all associated controllers has been developed. The performances of the system following a small disturbance at various operating conditions have been analyzed. To obtain quantitative estimates of the damping and synchronizing torques generated in the system, expressions for damping and synchronizing torque clients have been developed. With these analyses, the relative impact of the STATCOM and STATCOM with ES on system performance have been assessed. It is shown that with active and reactive power modulation capabilities effective and efficient control of small signal oscillations in power systems can be achieved.

With the increase of electric vehicles (EVs) on the roads the availability of charging infrastructure becomes more important. Today it is relatively straightforward to install fast chargers in areas with strong power grid connections, such as in urban areas. However, in areas with less available electrical power, the grid is considered to be a weak grid, typically in remote areas, which limits charging speeds. Local peak shaving can be implemented with battery energy storage systems (BESS) to support faster charging at these locations by increasing available power when needed. As the majority of the power is supplied by the BESS there are noticeable conversion losses when converting from the BESS DC voltage to AC in the grid and then back to DC through the fast charger. This thesis investigates DC/DC converters to charge EVs directly from a BESS DC bus by regulating the voltage to the level of the EV, while also supporting safe simultaneous charging capability. It was done through understanding relevant standards’ requirements, converter review, as well as design and simulation of the interesting topologies. The converters selected to simulate were the Buck-Boost and the Dual-Active Bridge (DAB). After analysing the efficiency result in combination with industry requirements, it was concluded that one DAB per output is the preferred option in most use cases. This would potentially also reduce the material usage and carbon footprint of this type of infrastructure compared to the current solution. Furthermore, some suggestions were made for improving the design of DAB converter before making a prototype for real testing. / Denna avhandling har undersökt hur en snabbladdares effektelektronik för en mobil batterienergilagringssystem kan designas för att ladda två elbilar samtidigt. För att göra detta har systemkrav från relevanta standarder sammanställts och olika snabbladdares kapacitet undersökts. Därefter har olika DC/DC-omvandlare identifierats i ändamål att välja ut de mest lämpade för att uppfylla funktionen. De utvalda omvandlarna designades iterativt och simulerades med i verktyget PLECS för att kunna jämföra hur vardera omvandlare presterade under olika scenarior och med olika transistorer. Resultat och slutsatser från detta arbete är att galvanisk isolering krävs mellan de två elbilarna samt att två Dual-Active Bridge (DAB) omvandlare är den mest lämpade utifrån effektivitet, kapacitet och materialanvänding. Det finns även flera områden att fortsätta arbetet på för att förbättra designen och testa med en prototyp.