Climate change is a subject of deep distress in today’s world. Over dependence on hydrocarbon has resulted in serious environmental problems. Rising sea level, global warming and ozone layer depletion are the mainstream of any discuss world over. The collective goal of cutting carbon emission by the year 2020has prompted the search for clean, alternative energy sources. This effort are already yielding good reward as other forms of energy such as solar, wind, nuclear and hydro have received huge investment and renew interest over the past decade. Thermoelectric materials over the past decades have been tipped to replace conventional means of power generations as these materials have the ability to convert heat to electrical energy and vice versa. They are simple, have no moving parts and use no greenhouse gases. But the major drawback of these materials is their low conversion efficiency. Hence there is a need to enhance the efficiency of thermoelectric material to fulfill their undeniable potentials. A parameter called the thermoelectric figure of merit, ZT defines the efficiency of a thermoelectric material. ZT relates three non-mutually exclusive transport properties namely Seebeck coefficient, electrical conductivity and thermal conductivity. Efficient thermoelectric material should possess high Seebeck coefficient, high electrical conductivity and low thermal conductivity. Hence, one of the interesting ideas in the area of thermoelectric research is the concept of designing a bulk material with high density of phonon scattering centers so has to reduce the lattice contribution to thermal conductivity but at the same time have minimum impact oncharge carriers. This is usually achieved by utilizing interphase and grain boundaries which are localized defects to scatter phonons. The volume fraction of the grain/interphase boundaries can be control through phase modification and microstructure design. This thesis is centered on Bi-Sb-Te systems which are the present room temperature state of the earth thermoelectric material. The investigation revolves around developing a new kind of microstructure in the well-studied Bi-Sb-Te system that shows tremendous potential as a means to reduce lattice contribution to thermal conductivity. The idea of having both p and n-type thermoelectric material preferably from the same material was also a motivation in our investigation. The thesis isdivided into six chapters. The first chapter introduces the concept of thermoelectricity i.e. the direct conversion of thermal energy into electricity. The physics involved and contribution of individual to the science of thermoelectricity were enumerated. Efficiency, optimization and material selection for better thermoelectric performance were briefly enumerated. Prospective materials that are currently been investigated for better thermoelectric properties were also mentioned. The structure of the Bi-Sb-Te system which is the focus of this thesis is present in this chapter including doping effect on the thermoelectric performance of the system as well as the various methods present been employed to improve the thermoelectric properties of the system. Finally the chapter enumerates the scope and object of the present thesis. The different experimental procedures adopted in the present thesis arediscussed in chapter 2. The details of different processing routes followed to synthesize flame-melted ingots, flame-melted + low temperature milled (cryo milling) + spark plasma sintering (SPS) alloy and flame-melted + melt spinning + spark plasma sintering (SPS) alloy, are discussed followed by the various structural and functional characterization techniques. The unique advantage of the spark plasma sintering techniques over the conventional sintering method was talked out in detail. The structural characterizations performed on the synthesized alloys include XRD, SEM and whilethe functional characterizations comprised of Hall measurement, Seebeck coefficient, electrical resistivity and thermal conductivity measurements. Thermoelectric properties of selected composition of Bi-Sb-Te synthesized via flame-melting are presented in chapter 3.Detail study of four analyzed compositions namelyBi24Sb20Te56, Bi20Sb12Te69, Bi16Sb5Te79 and Bi29Sb11Te60resulted in four unique microstructure and different volume fraction of primary and secondary phases. The resultant morphologies of the microstructure were observed to have influence the thermoelectric behavior corresponding to each composition. The sole influence of anti-structural defects on the conductivity type and the role of microstructure morphologies and length scale were understood in this chapter. Samples with segregated Te and a solid solution BiSbTe3(eutectic morphology) form an n-type thermoelectric material while samples with only solid solution BiSbTe3 forms a p-type thermoelectric material. Pair of n-type and p-type material was obtained without the introduction of external dopant.The pair shows good compatibility factorsuitable for thermoelectric device. In chapter 4, the thermoelectric properties of four selected composition of Bi-Sb-Te synthesized via low temperature milling plus spark plasma sintering is addressed. The analyzed compositions are as follows Bi24Sb20Te56, Bi18Sb11Te71, Bi17Sb6Te77, and Bi28Sb15Te57 respectively. The effect of low temperature milling combine with the prospect of minimum grain growth of spark plasma sintering on the thermoelectric properties of the selected compositions were determined. Samples with eutectic morphology which would otherwise scatter charge carriers were observed to have the highest carrier mobility as a result of high volume fraction of Te phase which serves as a donor injecting excess electrons into the system. The impact of small grain size was observed on the transport properties of the sample Bi28Sb15Te57 with the highest electrical resistivity, the best Seebeck coefficient and the lowest thermal conductivity. Pair of n-type and p-type material was obtained without the introduction of external doping elements. The pairshows good compatibility factor suitable for segmented thermoelectric device. Chapter 5 narrates the thermoelectric properties of four compositions namely Bi30Sb13Te58, Bi23Sb13Te65, Bi18Sb5Te77 and Bi23Sb20Te58subjected to melt spinning plus spark plasma sintering.High cooling rate obtained during melt spinning process was observed in this chapter to cause a shift of composition which resulted in a microstructure morphology with eutectic colonies that is predominantly Te rich. These Te rich colonies in the sample Bi30Sb13Te58 was observed to change the conductivity type of the sample from an otherwise p-type to n-type while also aiding bipolar conduction which was detrimental to the overall thermoelectric performance of the alloy. Segregated Te in the form of eutectic morphology helps to inject excess electron into the bulk of the sample Bi23Sb13Te65 and Bi18Sb5Te77hereby increases the observed electrical conductivity which by virtue of the microstructure morphology is expected to be low. As a result of the processing routes, all four compositions in this chapter shown-type conductivity. Chapter 6 presents the summary of the important conclusions drawn from this work.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-04-20T13:39:03Z No. of bitstreams: 1 pedromachadodealmeida.pdf: 13436160 bytes, checksum: 84c66613dade0766ae9ea2bdc8be9f91 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-04-20T14:45:37Z (GMT) No. of bitstreams: 1 pedromachadodealmeida.pdf: 13436160 bytes, checksum: 84c66613dade0766ae9ea2bdc8be9f91 (MD5) / Made available in DSpace on 2017-04-20T14:45:37Z (GMT). No. of bitstreams: 1 pedromachadodealmeida.pdf: 13436160 bytes, checksum: 84c66613dade0766ae9ea2bdc8be9f91 (MD5) Previous issue date: 2011-04-29 / Esta dissertação apresenta uma estratégia de controle para sistemas de geração fotovoltaicos, de único estágio, trifásicos, conectados à rede elétrica de distribuição. São desenvolvidos modelos matemáticos para representar as características dinâmicas dos painéis fotovoltaicos, do conversor fonte de tensão (VSC -“Voltage Source Converter”) e da rede de distribuição. A modelagem do sistema de geração disperso (SGD) é feita no sistema de coordenadas síncrono (dq), fornecendo um sistema de equações diferenciais que pode ser usado para descrever o comportamento dinâmico do sistema quando as tensões da rede estão equilibradas ou desequilibradas. O conversor é controlado no modo de corrente, através da estratégia de modulação vetorial (Space Vector Modulation - SVM). São projetadas duas malhas de controle em cascata para controlar o conversor estático. A malha interna controla a corrente injetada na rede enquanto que a externa controla a tensão no barramento CC do conversor. O controle da tensão CC permite rastrear o ponto de máxima potência do painel PV além de controlar a quantidade de potência ativa injetada na rede CA. Um método ativo de detecção de ilhamento baseado na injeção de corrente de sequência negativa é incorporado ao sistema de controle. Resultados de simulações digitais obtidos com o programa ATP (Alternative Transient Program ) são utilizados para validar os modelos matemáticos e as estratégias de controle. Finalmente, um protótipo experimental de pequena escala é montado em laboratório. Todo o sistema de controle do protótipo experimental foi implementado no DSP TMS320F28212. Os resultados obtidos demonstram o funcionamento do sistema e podem ser usados para validar a estratégia de controle utilizada. / This dissertation presents a control strategy for a single-stage, three-phase, photovoltaic systems to be connected to a distribution network. Mathematical models are developed to represent the dynamic characteristics of the photovoltaic panels, the voltage-source converter (VSC) and the distribution network. The modeling of the dispersed generation system (DGS) is done in the synchronous reference frame (dq), providing a system of differential equations that describes the dynamic behavior of the system when the network voltages are balanced or unbalanced. The converter is controlled in current mode through the space vector modulation (SVM) strategy. Two control loops are designed to control the static converter. The inner loop controls the injected current into the network while the external loop controls the converter DC bus voltage. The DC voltage regulator allows to track the PV maximum power point and to control the active power injected into the AC grid. An active islanding detection method based on negative-sequence current injection is incorporated into the control system. Digital simulations results obtained with Alternative Transients Program (ATP) is used to validate the mathematical models and the control strategies. Finally, a small-scale experimental prototype is implemented in the laboratory. The whole control system of the experimental prototype was programmed in DSP TMS320F2812 of Texas Instruments. The results demonstrate that the operation of the system can be used to validate the applied control strategy.

This work deals mainly with electrical energy. In the first part is focused on alternative energy sources, and describes structure of consumption and production of electricity over the past few years, during which is focuses on renewable energy sources. In this context, assesses the conditions for alternative energy sources in the Czech Republic from the perspective of the legislative, as well as current status and potential of alternative energy sources and tries to predict the development of these issues. The next section describes the Smart Grids as a means to achieve these goals. There are presented the basic features of this system, its goals and challenges, a description of the integration of Smart Grids with other sources of electricity and the benefits of using Smart Grids both from the perspective of user and from the perspective of system. Other parts are focused on distributed control systems in the energy sector, its development and principle. The last part is devoted to consideration of the role of alternative energy sources and distributed generation in Smart Grids.

The subject of thesis is environmental-friendly heating. Theoretical part includes overview of possible ways using alternative energy sources, especially solar energy and energy environment - heat pumps. Partical part is devoted to solution of environmental-friendly heating and heating warm water for family house using solar system. The proposal is documented with economic evaluation and calculation of economic return.

This master thesis studies alternative energy sources for maritime shipping in Sweden. With current climate goals, and a need for change, the maritime sector currently undergoes intense transitions. For shipping companies to lower their carbon footprint, the need to replace non decarbonised fuels is hence critical. With numerous alternatives, currently being developed, actors are phasing obstacles regarding which energy source that is most mature in terms of technical readiness as well as how adequate it will fulfil current climate goals. This study will analyse four different energy sources, liquid hydrogen (LH2), electro-methanol (emethanol), electro-ammonia (e-ammonia) and wind (sails), and answer which out of these energy sources will be most suitable for actors to adapt. To answer this question, the Technological Innovation System framework has been utilised, and the results has been applied to some chosen climate target actions developed by Swedish authorities. The findings proved that e-methanol currently is most mature and has reached most alignment with current climate goals, followed by LH2/wind and lastly e-ammonia. / Detta examensarbete studerar alternativa energikällor för fraktfartyg i Sverige. Med nuvarande klimatmål, och ett behov av förändring, genomgår den maritima sektorn intensiva omställningar. För att rederier ska kunna sänka sitt koldioxidavtryck är behovet att ersätta icke koldioxidneutrala bränslen därför stort. Med ett flertal alternativ, som för närvarande är under utveckling, står aktörer inför hinder angående vilken energikälla som är mest redo gällande teknikmognadsgrad samt hur adekvat den kommer att uppfylla nuvarande klimatmål. Denna studie kommer att analysera fyra olika energikällor, flytande väte (LH2), elektro-metanol (e-metanol), elektro-ammoniak (e-ammoniak) och vind (segel), och ta reda på vilka av dessa energikällor som är mest lämpad för aktörer att använda sig av. För att svara på denna fråga har ramverket Technological Innovation Systems använts och resultaten har tillämpats på några utvalda klimatmålsåtgärder som tagits fram av svenska myndigheter. Resultaten visade att e-metanol för närvarande är mest mogen och har nått mest anpassning till nuvarande klimatmål, följt av LH2/vind och slutligen e-ammoniak.

My doctoral thesis deals with use of the sophisticated methods for the selection of technical and economic solution of electrical wiring. This solution is based not only on a price but also on many other criteria such as a comfort, service, durability etc. The focus of the work is a treatise on wiring systems from a global perspective, where it is impossible to use a conventional approach for objective evaluation and selection of the appropriate electrical wiring system (because of the complexity of such systems and their interdependencies). In the four chapter are given information of an energy consumption (the total consumption and household consumption). In this chapter is given also a consumption prediction – especially for households. Following is an overview of possible measures for reducing electricity consumption in households. In the next part of this thesis are solved the knowledge, respectively expert systems for use in an electrical engineering – especially for a suitable tool for the selection and evaluation of households wiring electrical system. The result of this work provides a possible solution for a selection of wiring electrical system for households (focusing on the intelligent wiring) – from a technical and economic point of view and with using an innovative approach. The main contribution of this work is a proposal of the main part of the knowledge base. This base could be as a basis for knowledge, respectively for an evaluating technical and economical solution of an electrical wiring system – the expert system includes also a feedback function of an effectiveness solution, use value, price etc., which would also serve as a knowledge base.