Dissertationen zum Thema „Analysis of medium voltage distribution grid“

To provide electricity access to the population currently deprived of it, is one of the sustainable development goals. Although the number is decreasing and is below 1 billion people without access to electricity for the first time in the year 2017, there is still much to be done. At the current rate of electrification an additional approximately 550 million people of those deprived now would have access to electricity by the year 2030, but 650million would still be without electricity access. This report studies the spatial factors that affect how MV network expansion occurs. The motivation for this report comes from studying previous research work using GIS and studying the Open Source Spatial Electrification Tool (OnSSET) which is developed by the division of Energy Systems Analysis at KTH. The objective of this tool is to aid electrification planning by examining options ranging from national grid expansion to off-grid resources such as solar, wind, hydro based on spatial analysis of data. The study is conducted into two parts. First by undertaking a literature review of relevant GIS based electrification and utility planning articles, to identify the factors that contribute to the costs of grid network extension. Thereafter, existing grid networks in Malawi, Nigeria and Uganda have been analyzed to examine the correlation to the different factors identified in the literature review. A qualitative comparison is conducted between the different countries to aid the development of spatial analysis tools such as OnSSET. The observations made studying the countries in the Sub-Saharan Africa region are noted down in the results section depicting similarities in planning and implementation of the grid network. Finally, necessary suggestions are made that might supplement and help the efforts in geospatial electrification network planning tools like OnSSET. The differences between literature review and practical geospatial analysis tools is also mentioned including the challenges faced during this thesis.
Att kunna förse el till befolkningen som för närvarande ej har tillgång till det är ett av de globala hållbarhetsmålen. Även om andelen av befolkningen som inte har tillgång till el sjunker och befinner sig under 1 miljard för första gången år 2017, behöver mer göras. Vid nuvarande tillväxt av antalet människor som får tillgång till el kommer ytterligare 550 miljoner ha tillgång år 2030, men 650 miljoner kommer fortfarande vara utan. Denna rapport studerar de rumsliga faktorerna som påverkar sättet som utbyggnad av MV-nätverk sker. Motiveringen till denna rapport härrör från tidigare forskning med GIS och undersökningar av Open Source Spatial Electrification Tool (OnSSET) vilket är utvecklat av enheten för Energisystemanalys på KTH. Syftet med detta verktyg är att bistå planering för elektrifiering genom att analysera såväl utbyggnad av det nationella elnätet som fristående alternativ som sol-, vind- och vattenbaserade resurser med hjälp av spatiala dataanalyser. Denna undersökning genomförs i två delar. Den första delen behandlar litterära studier av relevanta GISbaserade studier för elektrifikations och nätverksplanering,, för att identifiera faktorer som bidrar till kostnaden av nätverkets expansion. Den andra delen behandlar existerande nätverk i Malawi, Nigeria och Uganda som har analyserats för att analysera korrelationen mellan de faktorer som identifierats i den litterära undersökningen. En kvalitativ jämförelse genomförs mellan de olika länderna för att bidra till utvecklingen av rumsliga analytiska verktyg som OnSSET. Observationerna som gjorts vid undersökningen i delen av Afrika söder om Sahara är noterade i resultatsektionen som skildrar likheter i planering och implementering av rutnätverken. Slutligen är nödvändiga förslag gjorda som möjligen kan bidra till och hjälpa i arbetet för geospatial elektrifikations planeringsverktyg som OnSSET. Skillnader mellan litterära undersökningen och praktiska geospatiala analysverktyg är också nämnd inklusive utmaningarna inför denna avhandling.

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.

Soft DC Links are power electronic converters enabling the control of power flow between distribution feeders or networks. This thesis considers the use of Soft DC Links in Medium Voltage (MV) distribution networks to improve network operation while facilitating the integration of distributed generators (DGs). Soft DC Links include Soft Open Points (SOPs) and Medium Voltage Direct Current (MVDC) links. An SOP can be installed to replace mechanical switchgear in a network, providing controllable active power exchange between connected feeders, as well as reactive power compensation at each interface terminal. The deployment of an MVDC link enables power and voltage controls over a wider area, and facilitates the effective use of available capacity between adjacent networks. The benefits of using SOP and MVDC link in MV distribution networks were investigated. A multi-objective optimisation framework was proposed to quantify the operational benefits of a distribution network with an SOP. An optimisation method integrating both global and local search techniques was developed to determine the set-points of an SOP. It was found that an SOP can improve network operation along multiple criteria and facilitate the integration capacity of DGs. A Grid Transformer-based control method of an MVDC link was proposed, which requires only measurements at the grid transformers to determine the operation of an MVDC link. Control strategies considering different objectives were developed. The proposed control method is used in the ANGLE-DC project, which aims to trial the first MVDC link in Europe by converting an existing AC circuit to DC operation. It was found that an MVDC link can significantly increase the network hosting capacity for DG connections while reducing network losses compared to an AC line. An impact quantification of Soft DC Links was carried out on statistically-similar distribution networks, which refer to a set of networks with similar but different topological and electrical properties. A model was developed to determine the optimal allocation of Soft DC Links. It was found that a Soft DC Link can reduce the network annual cost under a wide range of DG penetration conditions. The statistical analysis provides distribution network planners with more robust decisions on the implementation of Soft DC Links.

Rising penetration of renewable energy sources in electric power grids isboth a challenge and an opportunity to optimally utilize the potential of eitherwind or PV energy sources, to stabilize operation of future power systems.Bi-directional ows between distribution and transmission system operatorscause signicant problems with keeping the voltages in the grid within admissiblelimits. This paper contains description of Oland's island mediumandlow-voltage electric power grid, ranging from 0.4 kV to 130 kV in thepurpose of quasi-static analysis of active and reactive power ows in the system.Goal of the analysis is to optimize reactive power exchange at the pointof connection with the mainland grid. In the analyzed grid system, thereis an enormous, 190 % penetration of wind sources. Capacity of the windparks connected to dedicated buses totals to 136.1 MW, that supply up to90.5 MW of load. With industry-wise reactive power capability limits, totalcontribution of wind parks reaches almost 66 MVAr, enabling to compensatedecits and extra surpluses of the reactive power in the grid. Presentedsystem is connected to the mainland's grid through one point of connection,which is simulated as Thevenin equivalent circuit. Main objective of thethesis is to test and analyze viable solutions to minimize reactive power exchangeat the point of connection at Stavlo substation connecting Oland'sand Sweden's electric grid keeping valid all necessary contingencies enforcedby current grid codes applied in Sweden as well as thermal limits of the linesand voltage limits of the system. Furthermore, state of the art of currentreactive power compensation methodologies and most promising techniquesto eciently and eectively control reactive power ow are outlined. Droopcontrol methodologies, with focus on global and local objectives, and smartgrid solutions opportunities are being tested and modeled by the authors andare comprehensively presented in this paper. Moreover, economic costs ofcontrol methods are compared. Analysis of active power losses in the systemas well as cost of implementation of alternative solutions is presented, wheremost nancially viable solutions are outlined, giving brief outlook into futureperspectives and challenges of electric power systems. It is shown that controllabilityof reactive power support by wind turbine generators can enhanceoperation of electric power grids, by keeping the reactive power ow minimizedat the boundary between grids of distribution and transmission systemoperators. Furthermore, results indicate that extra reactive power supportby wind turbine generators can lead to diminishment of active power losses inthe system. Presented system is being modeled in the PSS/E software dedicatedfor power system engineers with use of Python programming languages.Analysis of data was done either in Python or R related environments. Thesiswas written with cooperation between KTH and E.On Energidistribution AB.
Hogre genomslagskraft av förnyelsebara energikällor i elnäteten är bådeen utmaning och möjlighet för att optimalt kunna utnyttja potentialen av vindkraft och PV källor, med avseende på att stabilisera driften av framtida elkraftsystem. Tvåvägsflöden mellan distributionoch transmissionsoperatörer orsakar betydande problem att hålla spänningen i nätet inom tillåtna gränsvärden.Denna uppsats innehåller en beskrivning av Ö lands mellanoch lågspänningsnät,på 0.4 kV till 130 kV i syftet att utföra en kvasistatisk analys av aktiva och reaktiva effektflöden i systemet. Målet med analysen är att optimera det reaktiva effektutbytet i kopplingspunkten med fastlandets nät. I det analyserade systemet, finns det en enorm potential på 190% genomslagskraft av vindkraft. Kapaciteten på vindkraftsparker kopplade till medtagna samlingsskenor i systemet uppgår till 136,1 MW, som tillgodoser upp till 90.5 MW last. Med industrimässigt begränsad reaktiv effektkapabilitet, uppgår vindkraftsparkernas bidrag till nästan 66 MVAr, vilken möjliggör kompensation för underskott och överskott av reaktiv effekt i nätet. Det presenterade systemet är kopplat till fastlandet genom en kopplingspunkt, där fastlandet är simulerat som en Thevenin ekvivalent. Huvudsakliga målet med denna uppsats är att testa och analysera gångbara lösningar för att minimera det reaktiva effektutbytet vid kopplingspunkten i Stävlö, som kopplar ihop Ö land med resterande nät i Sverige, samtidigt som alla nödvändiga villkor enligt nuvarande nätkoder i Sverige bibehålls, liksom termiska gränser för ledningarna och spanningsgränser för systemet. Ytterligare beskrivs den bästa tillgängliga tekniken som finns idag för reaktiv effektkompensation, och de mest lovande teknikerna för att effektivt och verkningsfullt kontrollera reaktiva effektflöden. Droop-kontroll-metodologier, med fokus på globala och lokala tillämpningar, och smarta nät-möjligheter testas och modelleras av författarna och presenterar djupgående i detta arbete. Dessutom jämförs ekonomiska kostnader för olika kontrollmetoder. Analyser av aktiva effektförluster i systemet samt kostnader för implementation av alternativa lösningar presenteras, där de flesta gångbara losningar behandlas, och ger en överskådlig bild av framtida perspektiv och utmaningar i elkraftsystemet. Det visas att vindturbiners kontroll av reaktiv effekt, kan förbättra driften av elnäten, genom att minimera det reaktiva effektflödesutbytet i gränsen mellan distributionoch transmissionsoperatörers nät. Ytterligare pekar resultat på att extra understöd av reaktiv effekt från vindturbiner kan leda till förminskning av aktiva förluster i systemet. Det presenterade systemet modelleras i mjukvaruprogrammet PSS/E dedikerat för elkraftsingenjörer med hjälp av Python. Analys av data gjordes antingen i Pythoneller R-relaterade miljöer. Detta arbete har gjorts tillsam-mans med KTH och E.ON Energidistribution AB.

The new generation of cars are so-called Plug-in Hybrid Electric Vehicles (PHEVs) which has the grid connection capability. By the introduction of these vehicles, the grid issues will be connected to the private car transportation sector for the first time. The cars from the gird perspective can be considered as a regular load with certain power factor. The effects of this type of new load in distribution grid are studied in this thesis. By modelling the cars as regular load, the effects of the cars in three distinct areas in Stockholm are investigated. The car number in each area is estimated based on the population and commercial density of electricity consumption in the three areas. Afterward, the average electricity consumption by the cars in one day is distributed among 24 hours of the day with peak load in the studied year. This distribution is done by two regulated and unregulated methods. The regulated method is based on the desired pattern of electricity consumption of PHEVs by vehicle owners. On the other hand, the regulated pattern is designed based on encouragement of the car owners to consume electricity for charging their car batteries at low-power hours of day (usually midnight hours). The power system from high voltage lines in Sweden down to 11 kV substations in Stockholm simulated in PSS/E software has been used in this study. The automation program (written in Python) is run in order to get the output report (voltage variation and losses) of the load flow calculations for different hours of day by adding the required power for PHEVs both by regulated and unregulated patterns. The results show the possibility of introducing growing number of cars till year 2050 in each area with existing grid infrastructures. Moreover, the number of cars, yearly and daily electric consumption for PHEVs in pure electric mode are shown in this project and the effects of regulated electricity consumption are investigated. It is concluded that since the car number is estimated based on the population, the areas with higher residential characteristics are more problematic for integration of PHEVs from capacity point of view. Moreover, by regulating the charging pattern of PHEVs, the higher number of PHEVs can be integrated to the grid with the existing infrastructures. In addition, the losses have been decreased in regulated pattern in comparison with unregulated pattern with the same power consumption. The voltage in different substations is within the standard boundaries by adding 100 percent of PHEVs load for both regulated and unregulated patterns in all three areas.

Recent research into industrial applications of electric power conversion shows an increase in the use of renewable energy sources and an increase in the need for electric power by the loads. The Medium-Voltage DC (MVDC) concept can be an optimal solution. On the other hand, the Modular Multilevel Converter (MMC) is an attractive converter topology choice, as it has advantages such as excellent harmonic performance, distributed energy storage, and near ideal current and voltage scalability. The fault response, on the other hand, is a big challenge for the MVDC distribution systems and the traditional MMCs with the Half-Bridge submodule configuration, especially when a DC short circuit fault happens. In this study, the fault current behavior is analyzed. An alternative submodule topology and a fault operation control are explored to achieve the fault current limiting capability of the converter. A three-phase SiC-based MMC prototype with the Full-Bridge configuration is designed and built. The SiC devices can be readily adopted to take advantage of the wide-bandgap devices in MVDC applications. The Full-Bridge configuration provides additional control and energy storage capabilities. The full in-depth design, controls, and testing of the MMC prototype are presented, including among others: component selection, control algorithms, control hardware implementation, pre-charge and discharge circuits, and protection scheme. Systematical tests are conducted to verify the function of the converter. The fault current behavior and the performance of the proposed control are verified by both simulation and experiment. Fast fault current clearing and fault ride-through capability are achieved.
Master of Science

Orientador : Prof. Dr. Alexandre Rasi Aoki
Coorientadores : Prof. Dr. Patricio Rodolfo Impinnisi ; Prof. Dr. Hans-Georg Schweiger
Dissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia Elétrica. Defesa: Curitiba, 22/05/2017
Inclui referências : p. 221-227
Resumo: A escassez de recursos, o aquecimento global e os desastres naturais aumentaram a conscientização ambiental e desencadearam notáveis esforços de transformação em todo o mundo, afastando da geração baseada em fontes fósseis para a geração de recursos energéticos renováveis na última década. A tendência global de Sistemas de Armazenamento de Energia Elétrica, especialmente as baterias, é uma promissora solução para a qualidade e segurança dos futuros sistemas de redes elétricas inteligentes com uma elevada quota de produção de energia renovável. A aplicabilidade e o desempenho técnico e econômico dos sistemas de baterias distribuídas dependem fortemente de múltiplas questões, que incluem a localização do projeto, o ambiente, as regulamentações do mercado da eletricidade, a aplicação, a tecnologia, a propriedade e o regime de remuneração. Desta forma, o conhecimento e as melhores práticas para a utilização da bateria distribuída, desenvolvidos em diferentes ambientes, não podem ser aplicados diretamente no cenário nacional, mas as circunstâncias e necessidades locais precisam ser estudadas e soluções adequadas e customizadas identificadas. Alinhada com os esforços mundiais em P&D para melhorar o desempenho técnico-econômico das tecnologias de baterias, a última solicitação pública de projetos estratégicos de P&D da Agência Nacional de Energia Elétrica (ANEEL) tem como objetivo identificar aplicações razoáveis e modelos de negócios para sistemas distribuídos de armazenamento de energia no Brasil. O objetivo deste trabalho é desenvolver um método para identificar como os sistemas distribuídos de baterias podem ser usados para melhorar a qualidade das redes de eletricidade renovável a nível nacional. Para isso, foi realizada uma pesquisa bibliográfica sobre os fundamentos das tecnologias e aplicações de baterias, seguida de uma coleta de dados sobre o estado da arte em P&D para sistemas de baterias distribuídas. O mercado brasileiro de eletricidade é estudado em termos de estrutura geral, partindo da participação e regulamentação relevante para geração distribuída e aplicação de armazenamento. Apresenta-se uma visão geral de todos os dados relevantes e do processo desenvolvido e detalhado, para identificar modelos de negócios apropriados para aplicação de bateria distribuída. Com base no resultado do último convite à apresentação de propostas do projeto estratégico de pesquisa e desenvolvimento, denominado Chamada 21, é criado um modelo para sistemas de armazenamento distribuído no Brasil para os próximos quatro anos, incluindo uma classificação das seis principais classificações de tipos e aplicações de baterias. A funcionalidade do método desenvolvido é comprovada pela identificação de um projeto exemplo de utilização distribuída do sistema de bateria para cada uma das classificações identificadas a partir do modelo brasileiro. Sob condições atuais de mercado e meio ambiente, esses projetos são simulados em termos de desempenho técnico-econômico com o programa de simulação de redes elétricas inteligentes no Homer Energy. Os resultados de custo e desempenho são comparados com soluções convencionais, para identificar a adequação de sistemas de baterias distribuídas e potenciais nichos de mercado. Em termos de eletrificações isoladas de fora da rede, em pequena escala, já foram identificados custos de operação global vantajosos. O método e o programa de simulação utilizado revelaram-se ferramentas razoáveis para identificar modelos de negócios para aplicações de bateria distribuída no Brasil e calcular as estruturas de cálculo de custos esperadas. Palavras-chave: Bateria, Modelo de Negócio, Baixa Tensão, Media Tensão, Brasil, Armazenamento de Energia Elétrica
Abstract: Resource scarcity, global warming and environmental disasters increased environmental awareness and unleashed remarkable worldwide transformation efforts away from fossil to renewable energy resources based generation during the last decade. There is a global trend for Electrical Energy Storage Systems (ESS) and especially batteries are one of the promising solutions for quality and safety in future, smart electricity networks with high shares of fluctuating renewable energy generation. Applicability and technical economic performance of distributed battery systems are strongly dependent on multiple issues, which include the project location, environment, electricity market regulations, application, technology, ownership and remuneration scheme. This way, knowledge and best practice for distributed battery utilization, developed in different environments, cannot be transferred directly to the national case, but local circumstances and needs have to be studied and appropriate, customized solutions identified. Aligned with the worldwide efforts on R&D to improve techno-economic performance of battery technologies, the latest public call for strategic R&D projects from the Brazilian Electricity Regulatory Agency - ANEEL, aims to identify reasonable applications and business models for distributed energy storage systems in Brazil. Objective of this work is to develop a method to identify how distributed battery systems can be used to improve the quality of renewable electricity networks on a nationalized level. To reach this, a literature research on the fundaments of battery technologies and applications, followed by a data collection on the state of the art in R&D for distributed battery systems are executed. The Brazilian electricity market is studied in terms of general structure, participation parties and relevant regulatory for distributed generation and storage application. An overview of all relevant data and the developed, detailed process, to identify appropriate business models for distributed battery application are presented. Based on the outcome of the last Public call for proposals from the strategic R&D project, known as Chamada 21, a roadmap for distributed storage systems in Brazil for the next four years is created, including a classification in six main classifications of battery types and applications. The functionality of the developed method is proved by identification of one exemplary project of distributed battery system utilization for each of the identified classifications from the Brazilian road map. Under current market and environment conditions, these projects are further simulated in terms of techno economic performance with the smart grid simulation program Homer Energy. The results of cost and performance are compared with conventional solutions, to identify the suitability of distributed battery systems and potential market niches. In terms of small scale, isolated off-grid electrifications there have been already advantageous overall operation cost identified. The method as well as the utilized simulation program turned out to be reasonable tools to identify business models for distributed battery applications in Brazil and calculate the expected costing structures. Keywords: Battery Energy Storage. Business Case. Low Voltage. Medium Voltage. Brazil. Electricity Storage.

Long term supporting schemes for photovoltaic (PV) system installation have led to accommodating large numbers of PV systems within load pockets in distribution grids. High penetrations of PV systems can cause new technical challenges, such as voltage rise due to reverse power flow during light load and high PV generation conditions. Therefore, new strategies are required to address the associated challenges. Moreover, due to these changes in distribution grids, a different response behavior of the distribution grid on the transmission side can be expected. Hence, a new equivalent model of distribution grids with high penetration of PV systems is needed to be addressed for future power system studies. The thesis contributions lie in three parts. The first part of the thesis copes with the PV modelling. A non-proprietary PV model of a three-phase, single stage PV system is developed in PSCAD/EMTDC and PowerFactory. Three different reactive power regulation strategies are incorporated into the models and their behavior are investigated in both simulation platforms using a distribution system with PV systems. In the second part of the thesis, the voltage rise problem is remedied by use of reactive power. On the other hand, considering large numbers of PV systems in grids, unnecessary reactive power consumption by PV systems first increases total line losses, and second it may also jeopardize the stability of the network in the case of contingencies in conventional power plants, which supply reactive power. Thus, this thesis investigates and develops the novel schemes to reduce reactive power flows while still keeping voltage within designated limits via three different approaches: decentralized voltage control to the pre-defined set-points developing a coordinated active power dependent (APD) voltage regulation Q(P)using local signals developing a multi-objective coordinated droop-based voltage (DBV) regulation Q(V) using local signals   In the third part of the thesis, furthermore, a gray-box load modeling is used to develop a new static equivalent model of a complex distribution grid with large numbers of PV systems embedded with voltage support schemes. In the proposed model, variations of voltage at the connection point simulate variations of the model’s active and reactive power. This model can simply be integrated intoload-flow programs and replace the complex distribution grid, while still keepingthe overall accuracy high. The thesis results, in conclusion, demonstrate: i) using rms-based simulations in PowerFactory can provide us with quite similar results using the time domain instantaneous values in PSCAD platform; ii) decentralized voltage control to specific set-points through the PV systems in the distribution grid is fundamentally impossible dueto the high level voltage control interaction and directionality among the PV systems; iii) the proposed APD method can regulate the voltage under the steady-state voltagelimit and consume less total reactive power in contrast to the standard characteristicCosφ(P)proposed by German Grid Codes; iv) the proposed optimized DBV method can directly address voltage and successfully regulate it to the upper steady-state voltage limit by causing minimum reactive power consumption as well as line losses; v) it is beneficial to address PV systems as a separate entity in the equivalencing of distribution grids with high density of PV systems.

The Doctoral Degrees issued upon completion of the programme are issued by Comillas Pontifical University, Delft University of Technology and KTH Royal Institute of Technology. The invested degrees are official in Spain, the Netherlands and Sweden, respectively. QC 20141028

Electricity grids require the ancillary services frequency control, grid operation, re-establishment of supply and voltage stability for a proper operation. Historically, conventional power plants in the transmission grid were the main source providing these services. An increasing share of decentralized renewable energy in the electricity mix causes decreasing dispatch times for conventional power plants and may consequently lead to a partial replacement of these technologies. Decentralized energy sources are technically capable of providing ancillary services. This work focuses on the provision of reactive power for voltage stability from decentralized sources. The aim is to answer the question of how voltage stability and reactive power management can be achieved in a future electricity system with increasing shares of decentralized renewable energy sources in an economical and efficient way. A methodology that takes reactive power and voltage stability in an electricity system into account is developed. It allows for the evaluation of the economic benefits of different reactive power supply options. A non-linear and a linearized techno-economic grid model are formulated for this purpose. The analysis reveals an increasing importance of reactive power from the distribution grid in future development scenarios, in particular if delays in grid extension are taken into account. The bottom-up assessment indicates a savings potential of up to 40 mio. EUR per year if reactive power sources in the distribution grid provide reactive power in a controlled manner. Although these savings constitute only a small portion of the total cost of the electricity system, reactive power from decentralized energy sources contributes to the change towards a system based on renewable energy sources. A comparison of different reactive power remuneration mechanisms shows that a variety of approaches exist that could replace the inflexible mechanisms of obligatory provision and penalized consumption of reactive power that are mostly in place nowadays.

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.

LiTH-ISY-EX--19/5194--SE

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
This dissertation presents a study of the operation of two different three-phase grid-connected test-grids with the connection of a 1MWp photovoltaic system. Two analysis methods are used to evaluate the impacts of this photovoltaic systeM, these methods being conventional static analysis and the analysis known as Quasi-Static Time-Series Analysis. Despite the fact that all grids have unique characteristics, it is important to use test-grids, which simulate the real grid characteristics, to analyze the kinds of problems that can occur and then look for alternatives, if necessary. The impacts evaluated are related to the system losses, minimized with the allocation study of the generation on the grid, voltage profile and tap position curve, when automatic load tap changers are used. It was verified that the photovoltaic system interconnection point is the most influenced one after its connection to the grid. The Quasi-Static Time-Series Analysis allow the correct evaluation of the load-generation interaction, running the time series power flow through estimated data for the load and irradiance curves during 168 hours. The conventional static analysis only considers critical operation conditions, like minimum and maximum load, and no generation or maximum generation, and does not evaluate different case scenarios that occur in reality. The photovoltaic systems can bring many advantages to the electric systems, like the improvement on the final consumer voltage profile, line losses reduction, and also environmental impacts reduction. However, with the increase of distributed photovoltaic generation on the electrical grid, it s necessary to be aware of the impacts that this may cause by performing interconnection studies.
Esta dissertação apresenta um estudo da operação de uma rede teste trifásica de média tensão com a interligação de um sistema fotovoltaico de 1,0 MWp. Dois métodos de análise são utilizados para avaliar os impactos deste sistema fotovoltaico, sendo estes métodos as análises estáticas convencionais eas análises conhecidas como Quasi-Static Time-Series Analysis. Apesar de cada rede elétrica apresentar características únicas, é importante a utilização de sistemas testes, que simulam as características de sistemas reais, para analisar que tipos problemas podem surgir e então buscar alternativas, se necessário. Os impactos avaliados se referem às perdas no sistema, minimizadas com a correta alocação da geração, perfil de tensão e curva de posição do tap, no caso de transformador com comutação automática de tap. Contata-se que o ponto de conexão do sistema fotovoltaico é o mais influenciado pela sua conexão à rede. As análises QSTS possibilitam avaliar corretamente a iteração entre carga e geração, efetuando o fluxo de potência consecutivo através de dados estimados para as curvas de carga e de irradiância solar ao longo de 168 horas. Já as análises convencionais consideram apenas condições críticas de operação, como por exemplo, carga leve ou nominal e geração nula ou máxima, não avaliando então diferentes cenários de operação que ocorrem na prática. Os sistemas fotovoltaicos podem trazer muitos benefícios aos sistemas elétricos, como melhoria do perfil de tensão de atendimento ao consumidor, redução de perdas nas linhas, além da redução nos impactos ambientais. Entretanto, com o aumento de geração fotovoltaica distribuída na rede, é necessário estar atento aos impactos que isto pode causar através de estudos de interconexão.

碩士
國立高雄海洋科技大學
輪機工程研究所
99
Medium voltage DC (MVDC) electrical distribution system that is a novel technique for sea and undersea vehicles has been extensively studied by ship building corporations and end-users in recent years. In this type of distribution systems, the steady-state stability issue is important because of the presence of different types of power converters and both of AC and DC power supply in the system. Power flow analyses can be carried to address this issue. This thesis aims to build a set of power flow analysis model for ship MVDC distribution systems with different types of power converters. A rigid power flow model of the power converters in steady-state is first. Derived to consider medium and low voltage characteristics of electric power system on this type of ship. A Newton-Raphson algorithm based unified AC/DC power flow solution model then is developed to incorporate AC-system and DC-system models and the AC/DC interface buses for system planning purpose. With the developed analysis model, the steady-state operating characteristics of the power-generation/distribution system and power converters for a given set of busbar loads and power generations in this type of distribution system can be accurately determined for providing a better system planning result. The analysis results can provide engineers useful information for planning and designing similar systems.

Indiana University-Purdue University Indianapolis (IUPUI)
This thesis presents a converter topology for photovoltaic panels. This topology minimizes the number of switching devices used, thereby reducing power losses that arise from high frequency switching operations. The control strategy is implemented using a simple micro-controller that implements the proportional plus integral control. All the control loops are closed feedback loops hence minimizing error instantaneously and adjusting efficiently to system variations. The energy management between three components, namely, the photovoltaic panel, a battery and a DC link for a microgrid, is shown distributed over three modes. These modes are dependent on the irradiance from the sunlight. All three modes are simulated. The maximum power point tracking of the system plays a crucial role in this configuration, as it is one of the main challenges tackled by the control system. Various methods of MPPT are discussed, and the Perturb and Observe method is employed and is described in detail. Experimental results are shown for the maximum power point tracking of this system with a scaled down version of the panel's actual capability.

Continued increase in system load leading to a reduction in operating margins, as well as the tendency to move towards a deregulated grid with renewable energy sources has increased the vulnerability of the grid to blackouts. Advanced intelligent techniques are therefore required to design new monitoring schemes that enable smart grid operation in a secure and robust manner. As the grid is highly interconnected, monitoring of transmission and distribution systems is increasingly relying on digital communication. Conventional security assessment techniques are slow, hampering real-time decision making. Hence, there is a need to develop fast and accurate security monitoring techniques. Intelligent techniques that are capable of processing large amounts of captured data are finding increasing scope as essential enablers for the smart grid. The research work presented in this thesis has evolved from the need for enhanced monitoring in transmission and distribution grids. The potential of intelligent techniques for enhanced system monitoring has been demonstrated for disturbed scenarios in an integrated power system. In transmission grids, one of the challenging problems is network partitioning, also known as network area-decomposition. In this thesis, an approach based on relative electrical distance (RED) has been devised to construct zonal dynamic equivalents such that the dynamic characteristics of the original system are retained in the equivalent system within the desired accuracy. Identification of coherent generators is another key aspect in power system dynamics. In this thesis, a support vector clustering-based coherency identification technique is proposed for large interconnected multi-machine power systems. The clustering technique is based on coherency measure which is formulated using the generator rotor measurements. These rotor measurements can be obtained with the help of Phasor Measurement Units (PMUs). In distribution grids, accurate and fast fault identification of faults is a key challenge. Hence, an automated fault diagnosis technique based on multi class support vector machines (SVMs) has been developed in this thesis. The proposed fault location scheme is capable of accurately identify the fault type, location of faulted line section and the fault impedance in the distributed generation (DG) systems. The proposed approach is based on the three phase voltage and current measurements available at all the sources i.e. substation and at the connection points of DGs. An approach for voltage instability monitoring in 3-phase distribution systems has also been proposed in this thesis. The conventional single phase L-index measure has been extended to a 3-phase system to incorporate information pertaining to unbalance in the distribution system. All the approaches proposed in this thesis have been validated using standard IEEE test systems and also on practical Indian systems.