• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 125
  • 13
  • 11
  • 8
  • 8
  • 3
  • 3
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 224
  • 110
  • 91
  • 70
  • 68
  • 66
  • 55
  • 43
  • 41
  • 38
  • 36
  • 35
  • 32
  • 32
  • 31
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
201

Sizing Methodology and Life Improvement of Energy Storage Systems in Microgrids

Khasawneh, Hussam Jihad 19 May 2015 (has links)
No description available.
202

Microgrid Optimal Power Flow Based On Generalized Benders Decomposition

Jamalzadeh, Reza 02 February 2018 (has links)
No description available.
203

Hierarchical Control of Inverter-Based Microgrids

Chang, Chin-Yao January 2016 (has links)
No description available.
204

Design of a Future Residential Hybrid Microgrid

Talaat Hifzy, Ahmad, Westermark, Wilhelm January 2021 (has links)
As we are moving towards a future carbon-neutralsociety, development of residential microgrids attracts much attentionaround the world with its efficient utilization of renewableenergy. A residential microgrid is a small power system fora house, which consists of a solar photovoltaic (PV) source,a battery storage, residential loads, and an interface to thegrid. In this paper, a hybrid AC-DC microgrid is proposed,studied and simulated in Matlab/Simulink. A coordinated controlstrategy is developed so that the PV converter is controlledto maximize its power generation, the battery converter iscontrolled to stabilize the system with the battery state of chargeconstraints, and an interlinking converter is controlled to decidethe connection/disconnection and the power flow with the grid.The simulation results show the effectiveness of the proposedsolution under various operating conditions. / I det här pappret föreslås, studeras ochsimuleras ett hybrid-anpassat lokalt självförsörjande elnät iSimulink och Matlab. Solpaneler utgör den distribueradeförnyelsebara energikällan i nätet. Panelerna styrs med enMPPT-algoritm för att maximera kraftgenereringen. Batterietsladdningstillstånd används i det designade batterilagringssystemetför att garantera lång livstid och för att fatta beslut omladdning och urladdning. Kraftöverföring mellan ACoch DCnätverk sker via en dubbelriktad omvandlare. Det konstrueradehybridnätet fungerar självständigt samt vid sammankopplingtill huvudnätet. Ett koordinerat kontrollsystem implementerasför att möjliggöra kommunikationen mellan lokalnätets olikadelar. Resultaten från simuleringstestet visar att det föreslagnanätet uppfyller stabilitetskrav och god funktion under varierandedriftstillstånd. / Kandidatexjobb i elektroteknik 2021, KTH, Stockholm
205

The Development of a DC Micro-grid model with Maximum Power Point Tracking for Waste Heat Recovery Systems

Elrakaybi, Ahmed 06 1900 (has links)
Research in sustainable energy sources has become the interest of many studies due to the increasing energy demand and the amount of wasted energy released from existing methods, along with their effect on climate change and environment sustainability. Thermo-Electric Generators (TEGs) are a potential solution that is being studied and implemented as they can convert low grade thermal energy to useful electrical energy at various operating conditions. The integration of a TEG within a heat exchanger (TEG/HX) system connected to an electrical DC micro-grid, using a Maximum Power Point Tracking (MPPT) system is the focus of this study. Using a numerical TEG/HX model from a previous study and a developed DC micro-grid model the interaction between the thermal and electrical aspects were investigated with the focus on the electrical performance of the system. The main concern of this study is to investigate the effect of the sub components of the DC micro-grid on the overall available energy. An analytic model was developed to estimate the power loss in the electrical circuit of the micro-grid, the model utilizes the equations for switching and conduction losses which have been used by several studies. Other variables such as the battery characteristics and electrical load profiles were also investigated by simulating several case studies including changing operating conditions. This study shows the effect of a TEG configuration on the power loss in an electrical system using power loss curves in comparison with the Open Circuit Voltage (OCV) of such configuration. It also covers important modes of operation for the battery, loads and MPPT for a stable and reliable operation of an isolated DC micro-grid system were TEGs are the only source of power. The result of the study presented is a system design that is able to maximize the electrical energy harvested from the TEGs to extend the operation of the dc-micro-grid first by applying a suitable TEG configuration and consequently a suitable electrical circuit. Secondly, by adapting to the changing operating conditions of the TEGs and the loads; and compensating for these changes using the battery storage system. / Thesis / Master of Applied Science (MASc)
206

Contribution to the Decentralized Energy Management of Autonomous AC-Microgrid / Contribution à la gestion décentralisée de l'énergie dans un micro-réseau AC autonome

Moussa, Hassan 07 July 2017 (has links)
Cette thèse porte sur des micro-réseaux AC isolées qui permettent l’intégration des ressources énergétiques distribuées (DER) pouvant fournir leur énergie d'alimentation existante de manière contrôlée pour assurer le bon fonctionnement global du système. L'interconnexion d'un DER à une micro-réseau s'effectue habituellement en utilisant un convertisseur d'interface distribué (DIC) (i.e. un bloc d'interface d'électronique de puissance générale) qui est constitué d’un module de convertisseur à l'entrée de la source, un onduleur de tension (VSI), un module d'interfaçage de sortie, et le module de commande. Dans cette thèse on réalise plusieurs lois de commande basées sur des méthodes décentralisées. L'accent principal est mis sur les fonctions "Droop" qui ont la tâche de maintenir un équilibre de distribution d'énergie entre les différentes sources énergétiques connectées à la micro-réseau. L'objectif est d'assurer la stabilité du système et d’améliorer les performances dynamiques en partageant la puissance entre les différents générateurs d’électricité distribués (DGs) en fonction de leur puissance nominale. Le développement d'une analyse de stabilité en boucle fermée s’avère utile pour étudier la dynamique du système afin d'obtenir une réponse transitoire souhaitée qui permet d'identifier les paramètres de contrôle de boucle appropriés. L'amélioration de la qualité d’énergie des micro-réseaux est également un objectif de cette thèse. La réduction des distorsions harmoniques de la tension de sortie en présence de charges linéaires et non linéaires est prise en compte dans nos travaux. D'autres aspects seront étudiés sur la façon de traiter les charges constantes connectées au réseau et les grandes perturbations qu’ils produisent. Cela donne lieu à d'autres études de recherche portant sur la stabilité grand signal des micro-réseaux / This thesis deals with islanded AC microgrid that allows any integration of Distributed Energy Resources (DERs) that may provide their existing supply energy in a controlled manner to insure overall system functioning. The interconnection of a DER to a microgrid is done usually by using a Distributed Interface Converter (DIC), a general power electronics interface block, which consists of a source input converter module, a Voltage Source Inverter module (VSI), an output interface module, and the controller module. The thesis realizes several control laws based on decentralized methods. The major focus is on the Droop functions that are responsible for providing a power distribution balance between different Energy Resources connected to a microgrid. The aim is to insure system stability and better dynamic performance when sharing the power between different DGs as function to their nominal power. Developing a closed loop stability analysis is useful for studying system dynamics in order to obtain a desired transient response that allows identifying the proper loop control parameters. Power Quality enhancement in microgrids is also a purpose of this research. The reduction of harmonic distortions of the output voltage when supplying linear and non-linear loads are taken in consideration in this thesis. Further aspects will be studied about how to deal with constant power loads connected to the grid and the large perturbations exerted. This results to further research studies that deal with large-signal stability of microgrids
207

Оптимално управљање микро мрежама у карактеристичним радним режимима / Optimalno upravljanje mikro mrežama u karakterističnim radnim režimima / Optimal Control of Microgrids in Different Operation Conditions

Selakov Aleksandar 12 September 2017 (has links)
<p>У дисертацији је дат концепт микро мрежа и описане постојеће методе у управљању и оптимизацији рада микро мрежа. Предложен је нови централизовани контролер микро мрежe заснован на технологији више-агентног система, који омогућава координацију три режима рада (повезани, острвски и хаваријски) и обезбеђује једноставну конфигурацију и комбинацију оптимизационих критеријума, уз уважавање широког скупа ограничења. Предложени модел примењен је на релевантни тест систем и резултати су приказани уз одговарајућу анализу резултата.</p> / <p>U disertaciji je dat koncept mikro mreža i opisane postojeće metode u upravljanju i optimizaciji rada mikro mreža. Predložen je novi centralizovani kontroler mikro mreže zasnovan na tehnologiji više-agentnog sistema, koji omogućava koordinaciju tri režima rada (povezani, ostrvski i havarijski) i obezbeđuje jednostavnu konfiguraciju i kombinaciju optimizacionih kriterijuma, uz uvažavanje širokog skupa ograničenja. Predloženi model primenjen je na relevantni test sistem i rezultati su prikazani uz odgovarajuću analizu rezultata.</p> / <p>Dissertation provides the microgrids concept and describes existing methods for control and optimization of microgrid operation. This paper proposes a novel, centralized, multi-agent-based, microgrid controller architecture, which provides the coordination of all three operation modes (grid-connected, island and emergency) and enables the easy configuration/combination of optimization goals that are subject to a given set of operational constraints.<br />The simulation results are presented for a typical microgrid test example.</p>
208

Dynamic optimization of energy systems with thermal energy storage

Powell, Kody Merlin 16 October 2013 (has links)
Thermal energy storage (TES), the storage of heat or cooling, is a cost-effective energy storage technology that can greatly enhance the performance of the energy systems with which it interacts. TES acts as a buffer between transient supply and demand of energy. In solar thermal systems, TES enables the power output of the plant to be effectively regulated, despite fluctuating solar irradiance. In district energy systems, TES can be used to shift loads, allowing the system to avoid or take advantage of peak energy prices. The benefit of TES, however, can be significantly enhanced by dynamically optimizing the complete energy system. The ability of TES to shift loads gives the system newfound degrees of freedom which can be exploited to yield optimal performance. In the hybrid solar thermal/fossil fuel system explored in this work, the use of TES enables the system to extract nearly 50% more solar energy when the system is optimized. This requires relaxing some constraints, such as fixed temperature and power control, and dynamically optimizing the over a one-day time horizon. In a district cooling system, TES can help equipment to run more efficiently, by shifting cooling loads, not only between chillers, but temporally, allowing the system to take advantage of the most efficient times for running this equipment. This work also highlights the use of TES in a district energy system, where heat, cooling and electrical power are generated from central locations. Shifting the cooling load frees up electrical generation capacity, which is used to sell power to the grid at peak prices. The combination of optimization, TES, and participation in the electricity market yields a 16% cost savings. The problems encountered in this work require modeling a diverse range of systems including the TES, the solar power plant, boilers, gas and steam turbines, heat recovery equipment, chillers, and pumps. These problems also require novel solution methods that are efficient and effective at obtaining workable solutions. A simultaneous solution method is used for optimizing the solar power plant, while a static/dynamic decoupling method is used for the district energy system. / text
209

Community Microgrids for Decentralized Energy Demand-Supply Matching : An Inregrated Decision Framework

Ravindra, Kumudhini January 2011 (has links) (PDF)
Energy forms a vital input and critical infrastructure for the economic development of countries and for improving the quality of life of people. Energy is utilized in society through the operation of large socio-technical systems called energy systems. In a growing world, as the focus shifts to better access and use of modern energy sources, there is a rising demand for energy. However, certain externalities result in this demand not being met adequately, especially in developing countries. This constitutes the energy demand – supply matching problem. Load shedding is a response used by distribution utilities in developing countries, to deal with the energy demand – supply problem in the short term and to secure the grid. This response impacts the activities of consumers and entails economic losses. Given this scenario, demand – supply matching becomes a crucial decision making activity. Traditionally demand – supply matching has been carried out by increasing supply centrally in the long term or reducing demand centrally in the short term. Literature shows that these options have not been very effective in solving the demand-supply problem. Gaps in literature also show that the need of the hour is the design of alternate solutions which are tailored to a nation's specific energy service needs in a sustainable way. Microgrids using renewable and clean energy resources and demand side management can be suitable decentralized alternatives to augment the centralized grid based systems and enable demand – supply matching at a local community level. The central research question posed by this thesis is: “How can we reduce the demand – supply gap existing in a community, due to grid insufficiency, using locally available resources and the grid in an optimal way; and thereby facilitate microgrid implementation?” The overall aim of this dissertation is to solve the energy demand – supply matching problem at the community level. It is known that decisions for the creation of energy systems are influenced by several factors. This study focuses on those factors which policy-makers and stakeholders can influence. It proposes an integrated decision framework for the creation of community microgrids. The study looks at several different dimensions of the existing demand – supply problem in a holistic way. The research objectives of this study are: 1. To develop an integrated decision framework that solves the demand – supply matching problem at a community level. 2. To decompose the consumption patterns of the community into end-uses. solar thermal, solar lighting and solar pumps and a combination of these at different capacities. The options feasible for medium income consumers are solar thermal, solar pumps, municipal waste based systems and a combination of these. The options for high income consumers are municipal waste based CHP systems, solar thermal and solar pumps. Residential consumers living in multi-storied buildings also have the options of CHP, micro wind and solar. For cooking, LPG is the single most effective alternative. 3. To identify the ‗best fitting‘ distributed energy system (microgrid), based on the end-use consumption patterns of the community and locally available clean and renewable energy resources, for matching demand – supply at the community level. 4. To facilitate the implementation of microgrids by * Contextualizing the demand – supply matching problem to consider the local social and political environment or landscape, * Studying the economic impact of load shedding and incorporating it into the demand-supply matching problem, and * Presenting multiple decision scenarios, addressing the needs of different stakeholders, to enable dialogue and participative decision making. A multi-stage Integrated Decision Framework (IDF) is developed to solve the demand - supply matching problem in a sequential manner. The first stage in the IDF towards solving the problem is the identification and estimation of the energy needs / end-uses of consumers in a community. This process is called End-use Demand Decomposition (EUDD) and is accomplished by an empirical estimation of consumer electricity demand based on structural and socio-economic factors. An algorithm/ heuristic is also presented to decompose this demand into its constituent end-uses at the community level for the purpose of identifying suitable and optimal alternatives/ augments to grid based electricity. The second stage in the framework is Best Fit DES. This stage involves identifying the “best-fit‘ distributed energy system (microgrid) for the community that optimally matches the energy demand with available forms of supply and provides a schedule for the operation of these various supply options to maximize stakeholder utility. It provides the decision makers with a methodology for identifying the optimal distributed energy resource (DER) mix, capacity and annual operational schedule that “best fits” the given end-use demand profile of consumers in a community and under the constraints of that community such that it meets the needs of the stakeholders. The optimization technique developed is a Mixed Integer Linear Program and is a modification of the DER-CAM™ (Distributed Energy Resources Customer Adoption Model), which is developed by the Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory using the GAMS platform. The third stage is the Community Microgrid Implementation (CMI) stage. The CMI stage of IDF includes three steps. The first one is to contextualize the energy demand and supply for a specific region and the communities within it. This is done by the Energy Landscape Analysis (ELA). The energy landscape analysis attempts to understand the current scenario and develop a baseline for the study. It identifies the potential solutions for the demand - supply problem from a stakeholder perspective. The next step provides a rationale for the creation of community level decentralized energy systems and microgrids from a sustainability perspective. This is done by presenting a theoretical model for outage costs (or load shedding), empirically substantiating it and providing a simulation model to demonstrate the viability for distributed energy systems. Outage cost or the cost of non supply is a variable that can be used to determine the need for alternate systems in the absence/ unavailability of the grid. The final step in the CMI stage is to provide a scenario analysis for the implementation of community microgrids. The scenario analysis step in the framework enlightens decision makers about the baselines and thresholds for the solutions obtained in the “best fit‘ analysis. The first two stages of IDF, EUDD and Best Fit DES, address the problem from a bottom-up perspective. The solution obtained from these stages constitutes the optimal solution from a technical perspective. The third stage CMI is a top-down approach to the problem, which assesses the social and policy parameters. This stage provides a set of satisficing solutions/ scenarios to enable a dialogue between stakeholders to facilitate implementation of microgrids. Thus, IDF follows a hybrid approach to problem solving. The proposed IDF is then used to demonstrate the choice of microgrids for residential communities. In particular, the framework is demonstrated for a typical residential community, Vijayanagar, situated in Bangalore and the findings presented. The End-use Demand Decomposition (EUDD) stage provides the decision makers with a methodology for estimating consumer demand given their socio-economic status, fuel choice and appliance profiles. This is done by the means of a statistical analysis. For this a primary survey of 375 residential households belonging to the LT2a category of BESCOM (Bangalore Electricity Supply Company) was conducted in the Bangalore metropolitan area. The results of the current study show that consumer demand is a function of the variables family income, refrigeration, entertainment, water heating, family size, space cooling, gas use, wood use, kerosene use and space heating. The final regression model (with these variables) can effectively predict up to 60% of the variation in the electricity consumption of a household ln(ElecConsumption) = 0.2880.396*ln(Income)+0.2 66*Refri geration+ 0.708*Entertainment+0.334*WaterHeating+0.047*FamSize+ 0243*SpaceCooling.+580*GasUse+0.421*WoodUse–0.159*KeroseneUse+ 0.568*SpaceHeating ln(ElecConsumption) = 0.406*ln(Income)0.168*Ref rigeration+0.139*Entertainment+ 0.213*WaterHeating+0.114*FamSize+0.121*SpacCooling+0.171*GasUse+ 0.115*WoodUse–0.094*KeroseneUse+0.075*SpaceHeating   The next step of EUDD is to break up the demand into its constituent end-uses. The third step involves aggregating the end-uses at the community level. These two steps are to be performed using a heuristic. The Best Fit DES stage of IDF is demonstrated with data from an urban community in Bangalore. This community is located in an area called Vijayanagar in Bangalore city. Vijayanagar is a mainly a residential area with some pockets of mixed use. Since grid availability is the constraining parameter that yields varying energy availability, this constraint is taken as the criteria for evaluation of the model. The Best Fit DES model is run for different values of the grid availability parameter to study the changes in outputs obtained in DER mix, schedules and overall cost of the system and the results are tabulated. Sensitivity analysis is also performed to study the effect of changing load, price options, fuel costs and technology parameters. The results obtained from the BEST Fit DES model for Vijayanagar illustrate that microgrids and DERs can be a suitable alternative for meeting the demand – supply gap locally. The cost of implementing DERs is the optimal solution. The savings obtained from this option however is less than 1% than the base case due to the subsidized price of grid based electricity. The corresponding costs for different hours of grid availability are higher than the base case, but this is offset by the increased efficiency of the overall system and improved reliability that is obtained in the community due to availability of power 24/7 regardless of the availability of grid based power. If the price of grid power is changed to reflect the true price of electricity, it is shown that DERs continue to be the optimal solution. Also the combination of DERs chosen change with the different levels of non-supply from the grid. For the study community, Vijayanagar, Bangalore, the DERs chosen on the basis of resource availability are mainly discrete DERs. The DERs chosen are the LPG based CHP systems which run as base and intermediate generating systems. The capacity of the discrete DERs selected, depend on the end-use load of the community. Biomass based CHP systems are not chosen by the model as this technology has not reached maturity in an urban setup. Wind and hydro based systems are not selected as these resources are not available in Vijayanagar. The CMI stage of IDF demonstrates the top-down approach to the demand-supply matching problem. For the Energy Landscape Analysis (ELA), Bangalore metropolis was chosen in the study for the purpose of demonstration of the IDF framework. Bangalore consumes 25% of the state electricity supply and its per capita consumption at 1560kWh is higher than the state average of 1230kWh and is 250% more than the Indian average of 612kWh. A stakeholder workshop was conducted to ascertain the business value for clean and renewable energy technologies. From the workshop it was established that significant peak power savings could be obtained with even low penetrations of distributed energy technologies in Bangalore. The feasible options chosen by stakeholders for low income consumers are The second step of CMI is finding an economic rationale for the implementation of community microgrids. It is hypothesized that the ‘The cost of non-supply follows an s-shaped curve similar to a growth curve.’ It is moderated by the consumer income, consumer utility, and time duration of the load shedding. A pre and post event primary survey was conducted to analyze the difference in the pattern of consumer behaviour before and after the implementation of a severe load shedding program by BESCOM during 2009-10. Data was collected from 113 households during February 2009 and July 2010. The analysis proves that there is indeed a significant difference in the number of uninterrupted power systems (inverters) possessed by households. This could be attributed mainly to the power situation in Karnataka during the same period. The data also confirms the nature of the cost of non-supply curve. The third step in CMI is scenario analysis. Four categories of scenarios are developed based on potential interventions. These are business-as-usual, demand side, supply side and demand-supply side. About 21 scenarios are identified and their results compared. Comparing the four categories of scenarios, it is shown that business-as-usual scenarios may result in exacerbation of the demand-supply gap. Demand side interventions result in savings in the total costs for the community, but cannot aid communities with load shedding. Supply side interventions increase the reliability of the energy system for a small additional cost and communities have the opportunity to even meet their energy needs independent of the grid. The combination of both demand and supply side interventions are the best solution alternative for communities, as they enable communities to meet their energy needs 24/7 in a reliable manner and also do it at a lower cost. With an interactive microgrid implementation, communities have the added opportunity to sell back power to the grid for a profit. The thesis concludes with a discussion of the potential use of IDF in policy making, the potential barriers to implementation and minimization strategies. It presents policy recommendations based on the framework developed and the results obtained.
210

Controle robusto de inversores VSI com filtro LCL aplicados a geração distribuída, com controle da injeção de potências ativa e reativa na rede de distribuição em baixa tensão e capacidade de operação ilhada em ambiente de microrredes / Robust control of voltage source inverters with LCL filters suitable for distributed generation, with control of the injection of active and reactive power on the low voltage distribution network and capability to operate in islanded mode in microgrid scenario

Pena, José Carlos Ugaz [UNESP] 02 June 2016 (has links)
Submitted by JOSÉ CARLOS UGAZ PEÑA null (josecarlos84@gmail.com) on 2016-06-20T13:29:30Z No. of bitstreams: 1 Tese_JoseCarlosPena_PPGEE.pdf: 9650212 bytes, checksum: 77b105d009c0b473cbc424e681ebe9a5 (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-06-22T13:10:00Z (GMT) No. of bitstreams: 1 pena_jcu_dr_ilha.pdf: 9650212 bytes, checksum: 77b105d009c0b473cbc424e681ebe9a5 (MD5) / Made available in DSpace on 2016-06-22T13:10:00Z (GMT). No. of bitstreams: 1 pena_jcu_dr_ilha.pdf: 9650212 bytes, checksum: 77b105d009c0b473cbc424e681ebe9a5 (MD5) Previous issue date: 2016-06-02 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Os inversores fonte de tensão com filtro de saída LCL (VSI+LCL) são amplamente utilizados em sistemas de geração distribuída. Nestas aplicações o sistema é controlado como uma fonte de corrente, no entanto, há a possibilidade de controlar o conjunto como uma fonte de tensão. Desta forma, a mencionada configuração pode ser utilizada em geração distribuída no ambiente de microrredes onde os sistemas, monofásicos ou trifásicos, devem operar conectados à rede de distribuição elétrica com controle das potências injetadas (ativa e reativa) e serem capazes de, em ausência da rede, passar a operar no modo autônomo. Ainda, após o restabelecimento da rede, o controle deve levar o sistema a operar novamente no modo conectado. Sendo as transições realizadas sem transientes que possam danificar qualquer componente do sistema. O filtro LCL, de terceira ordem, caracteriza um comportamento ressonante que pode comprometer a estabilidade do sistema. Para resolver esta situação, diversas técnicas ativas e passivas são aplicadas. Para aplicações de baixa potência, preferem-se as técnicas passivas de amortecimento devido a sua simplicidade e baixo custo, porém estas implicam em perdas adicionais. Já as técnicas ativas de amortecimento, consideram procedimentos de controle para atenuar a ressonância, e, portanto, não adicionam perdas, porém, sua realização requer da realimentação de variáveis adicionais elevando assim o custo do sistema. Todavia, mesmo que aplicáveis a ambos os modos de operação, as técnicas de amortecimento disponíveis na literatura consideram apenas um modo de operação. O presente trabalho de doutorado explora a possibilidade de controlar sistemas VSI+LCL, monofásicos e trifásicos, em ambos os modos de operação, com atenção a objetivos específicos em cada modo e transições suaves entre estes. Assim, são apresentadas duas estratégias de controle. A primeira estratégia considera o amortecimento da ressonância por técnicas passivas, mediante a utilização de um ramo de amortecimento de segunda ordem, projetado para garantir o efeito desejado em ambos os modos de operação e simplificar a dinâmica do sistema a fim de facilitar o projeto dos controladores, abordagem não utilizada nos métodos conhecidos na literatura. Logo, o sistema amortecido é controlado em uma configuração de duas malhas, controlando a corrente injetada mediante a tensão no capacitor. A segunda estratégia proposta considera a utilização de controladores por realimentação de estados em tempo discreto, sintetizados mediante desigualdades matriciais lineares, para simultaneamente, realizar ativamente o amortecimento da ressonância e atender os objetivos de controle em ambos os modos de operação. Ambas as estratégias propostas consideram controladores ressonantes com o objetivo de rastrear sinais senoidais de referência com erro nulo e suprimir componentes harmônicos de baixa ordem na corrente de saída. Ainda, os controladores são projetados considerando a necessidade de garantir a estabilidade robusta do sistema, isto é, frente a perturbações externas (tais como variações na carga local, oscilações na tensão do barramento CC ou distúrbios na rede) e às variações em parâmetros do sistema, como a indutância de rede. As propostas são apresentadas em detalhe, incluindo os procedimentos de projeto assim como critérios para a geração e coordenação dos sinais de controle e referência. As estratégias propostas são avaliadas experimentalmente sendo os resultados obtidos discutidos e analisados considerando-se as respectivas normas para os casos de operação conectada e ilhada. / The voltage source inverter utilization with LCL filters (VSI+LCL) is extended in Distributed Electrical Energy Systems. In these applications, the system is controlled as a current source, however, it can also be controlled as a voltage source. Hence, this configuration is suitable for microgrids environment. In this scenario, the system should operate connected to utility grid with control of the supplied power (active or reactive) and also be capable, in case of grid absence, to operate in islanded mode. Then, if the grid is reestablished, system should be reconnected to grid. Moreover, these transitions should be smooth, with no hazardous transients. The third order filter leads to a resonant behavior that can compromise the system stability. In order to overcome this limitation, passive and active damping methods are used. In low power applications, passive damping methods are preferred due to their simplicity and low. Nevertheless, these methods lead to additional losses. On the other hand, active damping methods consider the feedback of additional variables in order to damp the resonance in closed loop, with no additional losses. This implies additional sensors, thus increasing the overall cost. Despite their effectiveness to damp the resonance in both autonomous and grid connected applications, the most of the damping methods are usually designed only for a specific operation mode. This work explores the possibility to control VSI+LCL systems, single and three-phase, in both operation modes, attending to specific goals in each one, and with smooth transitions between them. For that purpose, two control strategies are proposed. The first one considers passive damping methods, by using a second order damping branch which is designed in order to guarantee the desired effect in both operation modes, thus simplifying the system dynamics in order to ease the control. This approach is not known in the literature. Then, the damped system is controlled in a two loop strategy, where the output current is controlled by means of the capacitor voltage. The second strategy considers the utilization of discrete time state-feedback controllers, synthesized by Linear Matrix Inequalities, in order to simultaneously achieve the active damping and the control goals for both operation modes. The proposed strategies use resonant controllers in order to achieve the tracking of sinusoidal references and to suppress low order harmonics in the output current. Moreover, controllers are designed to achieve robust stability of the system, thus, even in front of external disturbances (such as local load variations, DC bus oscillations or grid disturbances) and variation on system parameters, such as the grid inductance. The two introduced strategies are detailed including the design procedure and the criterion to generate and coordinate the reference and control signals. The two proposed strategies were experimentally verified. The results were analyzed and compared to the requirements imposed by the related standards for both modes of operation. / CNPq: 141757/2012-4

Page generated in 0.0319 seconds