Distributed generation (DG) with a converter interface to the power grid is found in many of the green power resources applications. This dissertation describes a multi-objective control technique of voltage source converter (VSC) based on multilevel converter topologies, for integration of DG resources based on renewable energy (and non-renewable energy)to the power grid. The aims have been set to maintain a stable operation of the power grid, in case of di erent types of grid-connected loads. The proposed method provides compensation for active, reactive, and harmonic load current components. A proportional-integral (PI) control law is derived through linearization of the inherently non-linear DG system model, so that the tasks of current control dynamics and dc capacitor voltage dynamics become decoupled. This decoupling allows us to control the DG output currents and the dc bus voltage independently of each other, thereby providing either one of these decoupled subsystems a dynamic response that signi cantly slower than that of the other. To overcome the drawbacks of the conventional method, a computational control delay compensation method, which delaylessly and accurately generates the DG reference currents, is proposed. The rst step is to extract the DG reference currents from the sensed load currents by applying the stationary reference frame and then transferred into synchronous reference frame method, and then, the reference currents are modi ed, so that the delay will be compensated. The transformed variables are used in control of the multilevel voltage source converter as the heart of the interfacing system between DG resources and power grid. By setting appropriate compensation current references from the sensed load currents in control circuit loop of DG link, the active, reactive, and harmonic load current components will be compensated with fast dynamic response, thereby achieving sinusoidal grid currents in phase with load voltages while required power of loads is more than the maximum injected power of the DG resources. The converter, which is controlled by the described control strategy, guarantees maximum injection of active power to the grid continuously, unity displacement power factor of power grid, and reduced harmonic load currents in the common coupling point. In addition, high current overshoot does not exist during connection of DG link to the power grid, and the proposed integration strategy is insensitive to grid overload. / La Generació Distribuïda (DG) injectada a la xarxa amb un convertidor estàtic és una solució molt freqüent en l'ús de molts dels recursos renovables. Aquesta tesis descriu una técnica de control multi-objectiu del convertidor en font de tensió (VSC), basat en les topologies de convertidor multinivell, per a la integració de les fonts distribuïdes basades en energies renovables i també de no renovables.Els objectius fixats van encaminats a mantenir un funcionament estable de la xarxa elèctrica en el cas de la connexió de diferents tipus de càrregues. El mètode de control proposat ofereix la possibilitat de compensació de les components actives i reactives de la potencia, i les components harmòniques del corrent consumit per les càrregues.La llei de control proporcional-Integral (PI) s’obté de la linearització del model inherentment no lineal del sistema, de forma que el problema de control del corrent injectat i de la tensió d’entrada del convertidor queden desacoblats. Aquest desacoblament permet el control dels corrents de sortida i la tensió del bus de forma independent, però amb un d’ells amb una dinàmica inferior.Per superar els inconvenients del mètode convencional, s’usa un retard computacional, que genera les senyals de referència de forma acurada i sense retard. El primer pas es calcular els corrents de referència a partir de les mesures de corrent. Aquest càlcul es fa primer transformant les mesures a la referència estacionaria per després transformar aquests valors a la referència síncrona. En aquest punt es on es poden compensar els retards.Les variables transformades son usades en els llaços de control del convertidor multinivell. Mitjançant aquests llaços de control i les referències adequades, el convertidor és capaç de compensar la potencia activa, reactiva i els corrents harmònics de la càrrega amb una elevada resposta dinàmica, obtenint uns corrents de la xarxa de forma completament sinusoïdal, i en fase amb les tensions.El convertidor, controlat amb el mètode descrit, garanteix la màxima injecció de la potencia activa, la injecció de la potencia reactiva per compensar el factor de potencia de la càrrega, i la reducció de les components harmòniques dels corrents consumits per la càrrega. A més, garanteix una connexió suau entre la font d’energia i la xarxa. El sistema proposat es insensible en front de la sobrecarrega de la xarxa

Existing petroleum and natural gas reserves, which are the major supplies of primary energy demand of the world, are cumulated in a few countries. This causes a serious supply security problem for many countries. On the other side, greenhouse gas emissions caused by mainly fossil fuels are gradually increasing to a point which jeopardizes the future of the earth. By now, countries have to consider both their supply security and this global environmental problem while planning their energy future. For Turkey, a developing country, economic growth is to be added as a third parameter of the solution of this energy equation. In this study, firstly, Turkey&#039 / s existing fossil and alternative energy resources potential is examined. In the second part, international acts against climate change problem and Turkey&#039 / s position in this issue is analyzed. In the third part, the relation between economic growth, energy and environment is discussed. Finally, in consideration with supply security, climate change and economic growth, a brief analyze for Turkey is performed. Study shows that these three parameters are strongly interconnected, especially for fossil resources this leads to some conflictual situations. Comparing with OECD countries, energy is an important factor for economic growth in Turkey. Depending on this fact, Turkey can better give priority to supply security and take an environmental responsibility appropriate to its special condition. It is concluded that Turkey should start with the emission mitigation methods which do not threaten the supply security much, such as forestation, energy conservation and efficiency. Since coal is predicted to continue its popularity in the future, clean coal technologies and carbon capture-storage options gain more importance. For long term, state-sanctioned utilization of renewable resources and carefully planned nuclear development are found to be the most promising solutions for replacing coal and imported natural gas in power generation.

The increasing demand for energy and the increased depletion rate of nonrenewable energy resources call for research on renewable alternatives. Mapping the availability of these resources is an important step for development of energy conversion projects. For this purpose, the wave power potential along the Atlantic coast of the southeastern USA, and the tidal stream power along the coast of Georgia are investigated in this study. Wave power potential is studied in an area bounded by latitudes 27 N and 38 N and longitudes 82 W and 72 W (i.e. North Carolina, South Carolina, Georgia, and northern Florida). The available data from National Data Buoy Center wave stations in the given area are examined. Power calculated from hourly significant wave heights and average wave periods is compared to power calculated using spectral wave energy density. The mean power within 50 km of the shore is determined to be low, whereas higher power is available further offshore beyond the 3500 m contour line. The tidal stream power potential along the coast of the state of Georgia is evaluated based on the NOAA tidal predictions for maximum tidal currents and three dimensional numerical modeling of the currents with Regional Ocean Modeling System (ROMS). The modeling results are validated against the available measurements. This region has low to moderate average tidal currents along most of the coast, but with the possibility of very strong local currents within its complex network of tidal rivers and inlets between barrier islands. Tidal stream power extraction is simulated with a momentum sink in the numerical models at the estuary scale to investigate effect of power extraction on the estuarine hydrodynamics. It is found that different power extraction schemes might have counterintuitive effects on the estuarial hydrodynamics and the extraction efficiency. A multi-criteria method that accounts for the physical, environmental and socioeconomic constraints for tidal power conversion schemes is proposed to select favorable locations and to rank them according to their suitability. For this purpose, the model results are incorporated into a Geographical Information System (GIS) database together with other geospatial datasets relevant to the site selection methodology. The methodology is applied to the Georgia coast and the candidate areas with potential are marked.

No description available.

A modern town is comprised of complex interrelations between socio-political, environmental and economical subsystems. Every city is a framework directed by local inhabitant’s needs and is filled with the ideas of local planners, local and global economical conditions and consequently it is crucial to find reasonable technological solutions. These solutions should shape the sustainable urban environment and the urban transport system is a substantial part of this environment. The quality and supply of transport services very closely relate to environmental aspects and are one of the main indicators showing the quality of life in cities. Transport is the most energy intensive sector of transport and is viewed as a key challenge for sustainable development. Transport causes pollution that has adverse effects on the environment at the local, regional and global levels and harms human health. Integrated approaches to transportation that include improved planning, demand management, fuel efficiency and cleaner fuels can help to meet transport’s challenges. There are three main groups of tools to reduce fuel consumption and emissions: technological, administrational, and planning. One of the main strategic objectives of the Lithuanian transport sector is development of its infrastructure, increase of transport flows and energy efficiency. Therefore, the Lithuanian policy is orientated to secured operation, traffic safety, reduction of environmental impacts, market regulation and... [to full text]

Magistro baigiamajame darbe nagrinėjama energetinių išteklių naudojimo (gamyboje, tiekime, vartojime) apimtis bei būdus Lietuvos ūkyje, siekiama įvertinti energetinių išteklių naudojimo ekonominį efektyvumą Lietuvos ūkio sektoriuose (pramonėje, statyboje, žemės ūkyje, transporte, paslaugų sektoriuje, namų ūkiuose) ir nustatyti energetinių išteklių naudojimo ekonominį efektyvumą įtakojančius veiksnius. / The aim of the master‘s thesis is to examine the methods and the volume of energy resource usage (in production, supply and consume) in Lithuanian economy, to evaluate the economic efficiency of energy resource usage in Lithuanian economic sectors(industry, construction, agriculture, transport, services and households) and to determine factors influencing the economic efficiency of energy resource usage.

A modern town is comprised of complex interrelations between socio-political, environmental and economical subsystems. Every city is a framework directed by local inhabitant’s needs and is filled with the ideas of local planners, local and global economical conditions and consequently it is crucial to find reasonable technological solutions. These solutions should shape the sustainable urban environment and the urban transport system is a substantial part of this environment. The quality and supply of transport services very closely relate to environmental aspects and are one of the main indicators showing the quality of life in cities. Transport is the most energy intensive sector of transport and is viewed as a key challenge for sustainable development. Transport causes pollution that has adverse effects on the environment at the local, regional and global levels and harms human health. Integrated approaches to transportation that include improved planning, demand management, fuel efficiency and cleaner fuels can help to meet transport’s challenges. There are three main groups of tools to reduce fuel consumption and emissions: technological, administrational, and planning. One of the main strategic objectives of the Lithuanian transport sector is development of its infrastructure, increase of transport flows and energy efficiency. Therefore, the Lithuanian policy is orientated to secured operation, traffic safety, reduction of environmental impacts, market regulation and... [to full text]

This thesis first develops a medium-voltage grid code outlining stringent requirements for low-voltage ride-through, high-voltage ride-through and ancillary services based on anticipated grid requirements for distributed energy resources (DER)s. A 100 kW generating capacity DER study system is then formulated taking into consideration key design constraints as motivated by the medium-voltage grid code. Local DER system controls are developed that enable existing systems employing conventional current-control for the grid-interfacing voltage-sourced-converters to comply with the grid code. A supervisory controller is proposed that allows multiple DER units and loads to operate collectively as a DER system with a single point of common coupling. The impact of transformer configurations, fault types and fault locations on DER systems are quantified through a comprehensive fault study using the PSCAD/EMTDC software package. A subset of these fault scenarios are identified for rapid screening of DER system compliance against low-voltage ride-through requirements.

This thesis first develops a medium-voltage grid code outlining stringent requirements for low-voltage ride-through, high-voltage ride-through and ancillary services based on anticipated grid requirements for distributed energy resources (DER)s. A 100 kW generating capacity DER study system is then formulated taking into consideration key design constraints as motivated by the medium-voltage grid code. Local DER system controls are developed that enable existing systems employing conventional current-control for the grid-interfacing voltage-sourced-converters to comply with the grid code. A supervisory controller is proposed that allows multiple DER units and loads to operate collectively as a DER system with a single point of common coupling. The impact of transformer configurations, fault types and fault locations on DER systems are quantified through a comprehensive fault study using the PSCAD/EMTDC software package. A subset of these fault scenarios are identified for rapid screening of DER system compliance against low-voltage ride-through requirements.

After the Soviet dissolution, the newly independent post-Soviet state of Azerbaijan intensified its efforts at developing its relations with the United States. Based on the analysis of the Azerbaijan&ndash / U.S. relations between1991-2006, the thesis tries to answer which factors could account for the existing political problems between these countries, given that both countries have a common interest in deepening their cooperation concerning the Caspian energy resources as well as the fight against international terrorism. This thesis argues that although both countries have many interests in common, they are unable to deepen their level of cooperation because of the Nagorno-Karabakh problem which, since it breaches the territorial integrity of Azerbaijan, is that state&rsquo / s main priority. The thesis has four main chapters: after a general overview of the evolution of Azerbaijan&rsquo / s foreign policy in the post-Soviet era and the U.S. policies towards the Caucasus, I examine Azerbaijan&rsquo / s cooperation with the U.S. in the field of energy, the Nagorno-Karabakh problem in Azerbaijan&rsquo / s relations with the U.S., and Azerbaijan&rsquo / s cooperation with the U.S. in the fight against international terrorism. In this thesis I focus on these three interests of Azerbaijan in its relations with the U.S. because in analyzing this country&rsquo / s foreign policy these are vital issues that include economic development, territorial integrity and its global political role concerning security.