436 research outputs found
Renewable Energy Systems:Technology Overview and Perspectives
No full textIn this chapter, essential statistics demonstrating the increasing role of renewable energy generation are first discussed. A state-of-the-art review section covers the fundamentals of wind turbine and photovoltaic (PV) systems. Schematic diagrams illustrating the main components and system topologies are included. Also, the increasing role of power electronics is explained as an enabler for renewable energy integration and for future power systems and smart grids. Recent examples of research and development, including new devices and system installations for utility power plants and for residential and commercial applications, are provided. Fuel cells, solar thermal, wave generators, and energy storage systems are also briefly presented and illustrated. Challenges and future trends for the technologies in 2025 are summarized in a table for onshore and offshore wind energy; solar power, including PV and concentrating solar power; wave energy; fuel cells; and storage with batteries and hydrogen, respectively. Recommended further readings on topics of electric power engineering for renewable energy are included in the final section
Power Electronics and Controls for Large Wind Turbines and Wind Farms
No full textWind power represents a major and growing source of renewable energy for electric power systems. This chapter provides an overview of state-of-the-art technologies and anticipated developments in the area of power electronic drives, controls, and electric generators for large multi-megawatt (MW) wind turbine (WT) systems. The principal components employed in a turbine for energy conversion from wind to electricity are described, and the main solutions that are commercially available are briefly reviewed. The specific issues of complex mission profiles, grid codes, and also reliability are discussed. The topics of power electronics, ranging from devices to circuit topologies, ans similar matters for electric generators, together with the results of optimal design studies are included. It is shown that the individual power rating of WTs has increased over the years and technologies required in order to reach and even exceed a power rating of 10 MW are discussed. The role of power electronics for improving the operation of WTs and ensuring compliance with power grid codes is analyzed with a view to produce fully controllable generation units suitable for a tight integration into the power grid and large-scale deployment in the future smart power systems
Electric Generators and their Control for Large Wind Turbines
No full textThe electric generator and its power electronics interface for wind turbines (WTs) have evolved rapidly toward higher reliability and reduced cost of energy in the last 40 years. This chapter describes the up-to-date electric generators existing in the wind power industry, namely, the doubly fed induction generator, the cage rotor induction generator, and the synchronous generator with DC or permanent magnet excitation. The operating principle, performance, optimal design, and the modeling and control of the machine-side converter for each kind of generator are adressed and evaluated. In view of the fact that individual power rating of WTs has increased to around 10 MW, generator design and control technologies required to reach this power rating are discussed
Configurations of Modified SEPIC Converter with Switched Inductor Module (MSCsI) for Photovoltaic Application: Part-II
No full textThe proposed work is extended configurations of Modified SEPIC Converter (MSC) and Modified SEPIC Converter with Switched Module (MSCSI). The proposed three configurations are derived by replacing two inductor of MSC by two Switched Inductor (SI) modules, namely Modified SEPIC Converter with XYL configuration (MSCSI-XYL), Modified SEPIC Converter with LYZ configuration (MSCSI-LYZ) and Modified SEPIC Converter with XLZ configuration (MSCSI-XLZ) to improve or increase the overall gain of the converter. The key feature of proposed configuration is: (i) single switch topologies, (ii) no reverse current flow from load to source due to large inductor at the input side, (iii) high voltage conversion ratio. The detailed analysis of three configurations is done in terms of component count, voltage conversion ratio and efficiency. The mathematical analysis and simulation results validates the functionality of three configurations
On the Charge-Transfer Excitations in Azobenzene Maleimide Compounds: A Theoretical Study
No full textPhotoswitchable systems with charge-transfer (CT) transitions have gained much attention during the recent years because of their many emerging applications. CT transitions themselves are of fundamental importance from physical, chemical, engineering, and molecular modeling points of view because they depend on the modified intramolecular electronic structure. CT transitions in azobenzene (AB) were observed when substituted with the maleimide (MI) functional group. This work represents a systematic theoretical study of excited states of the AB–MI structures of eight azo derivatives. In addition to the two main azo transitions (π → π* and n → π*), our calculations show a CT occurring between the azo moiety as a donor and the MI group as an acceptor. The CT mechanism can be characterized based on both the number and the position of the MI fragments. MI groups in the azo structure result in low-energy transitions, changing the order of the main transitions by introducing a CT character. Calculations using both density functional theory (DFT) and high-end molecular orbital theories confirm the CT character of these derivatives, although the order of excited states was found to differ depending on the chosen level of theory. We present here the first theoretical investigation of the electronic excited states (nπ*CT and ππ*CT) and corresponding transitions for this class of compounds. The computational results showed that the CT mechanism in AB–MI derivatives can occur via two pathways: planar and twisted. Our findings are expected to be of substantial interest, especially in the area of molecular optoelectronics and in the design of responsive materials
Conexão série-série de módulos CC-CC isolados
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2015Esta tese apresenta a associação de conversores CC-CC de duas portas conectados em série-série tanto na versão unidirecional quanto na versão bidirecional com comando único de controle. Inicialmente é realizado um estudo sobre os conversores CC-CC isolados bidirecionais de duas portas onde é proposta uma classificação para estes conversores com base no fluxo magnético de seus respectivos transformadores. Na sequência é realizado um estudo sobre a conexão série na entrada e série na saída de módulos CC-CC com característica externa em queda de tensão onde se verifica que para este tipo de módulo é possível realizar tal conexão de modo que haja equilíbrio nas tensões individuais dos módulos em ambos os lados da conversão sem a necessidade do uso de malhas de controle. Por apresentar característica externa em queda de tensão tanto no modo de condução contínua quanto no modo de condução descontínua, o conversor CC-CC isolado Ponte Completa com saída em tensão é estudado e utilizado como unidade modular da versão unidirecional da conexão série-série. O mecanismo de balanço da conxão série-série unidirecional é demonstrado analiticamente e comprovado via simulação. Resultados experimentais da conexão sériesérie unidirecional são obtidos a partir de um protótipo de 4 módulos, 4 kW, 1600V na entrada, 1600V na saída, 40 kHz e incluem operação em malha aberta, degrau na tensão de entrada e degrau de carga. O conversor Dual Active Bridge  DAB é estudado e utilizado como unidade modular da versão bidirecional da conexão série-série. Verificou-se analiticamente que na conexão série-série de módulos DAB sem perdas as tensões nos capacitores de cada módulo, tanto do lado  A quanto do lado  B da conversão, oscilam indefinidamente quando há um desequilíbrio nestas tensões, porém, ocorre o equilíbrio nestas tensões em termos de valores médios. Para a extinção das referidas oscilações é necessário que haja perdas de modo a proporcionar amortecimento para anulação das oscilações. Resultados experimentais da conexão série-série bidirecional são obtidos a partir de um protótipo de 4 módulos, 4 kW, 1600V no lado  A , 1600V no lado  B , 40 kHz e incluem operação em malha aberta com fluxo direto e operação em malha aberta com fluxo direto e reverso de modo a comprovar a bidirecionalidade do conversor. Abstract : This thesis presents the association of DC-DC converters with two ports connected in series-series in both unidirectional and bidirectional version with single control. Initially is carried out a study on the isolated bidirectional DC- DC converters with two ports where it is proposed a classification for these converters based on magnetic flux in their transformers. In the sequence is carried out a study on the modular input-series and output-series connection of DC-DC converters with external characteristic type voltage drop where it can be seen that for this type of module it is possible to perform such a connection, so that there is balance in voltages of individual modules in both sides of the conversion without the need to use a control loop. By presenting external characteristic type voltage drop in both continuous conduction as in discontinuous conduction mode, the isolated DC-DC converter Full Bridge with voltage output is studied and used as a modular unit of unidirectional series-series connection version. The unidirectional series-series connection balance mechanism was analytically demonstrated and proven by simulation. Experimental Results of unidirectional series-series connection are obtained from a prototype with 4 modules, 4 kW, 1600 Vdc input, 1600 Vdc output, 40 kHz and include operation in open-loop, step on the input voltage and step load. The Dual Active Bridge  DAB converter is studied and used as a modular unit of bidirectional series-series connection version. It was verified analytically that in the series-series connection of lossless DAB modules the voltages across the capacitors of each module, both the side "A " and the "B" side of the conversion, oscillate indefinitely if there is an imbalance in these voltages, however, occurs balancing in these voltages in terms of average values. To extinguish these oscillations it is required losses to provide damping for cancellation of oscillations. Experimental results of the bidirectional series-series connection are obtained from a prototype with 4 modules, 4 kW, 1600 Vdc in side A, 1600 Vdc on side B, 40 kHz and include operation in open loop with direct power flow and operation in open loop with direct and reverse power flow in order to prove the bidirectional capability of the converter
Analysis and design of a two-speed single-phase induction motor with 2 and 18 pole special windings
No full textThe motor presented employs multiple independent windings for operation with two very different pole numbers. The 18-pole field is produced with a symmetrical three-phase winding connected in a Steinmetz arrangement to a single-phase supply. A unified analysis method has been developed and used to demonstrate the equivalence of a Steinmetz delta or star connection with a main and auxiliary winding of a single-phase motor. The method has been experimentally validated and also included are some specific motor design considerations
Computation of core losses in electrical machines using improved models for laminated steel
No full textTwo new models for specific power losses in cold-rolled motor lamination steel are described together with procedures for coefficient identification from standard multifrequency Epstein or single sheet tests. The eddy-current and hysteresis loss coefficients of the improved models are dependent on induction (flux density) and/or frequency, and the errors are substantially lower than those of conventional models over a very wide range of sinusoidal excitation, from 20 Hz to 2 kHz and from 0.05 up to 2 T. The model that considers the coefficients to be variable, with the exception of the hysteresis loss power coefficient that has a constant value of 2, is superior in terms of applicability and phenomenological support. Also included are a comparative study of the material models on three samples of typical steel, mathematical formulations for the extension from the frequency to the time domain, and examples of validation from electrical machine studies
Overview of Maximum Power Point Tracking Techniques for Photovoltaic Energy Production Systems
No full textA substantial growth of the installed photovoltaic (PV) systems capacity has occurred around the world during the last decade, thus enhancing the availability of electric energy in an environmentally friendly way. The maximum power point tracking (MPPT) technique enables to maximize the energy production of PV sources, despite the stochastically varying solar irradiation and ambient temperature conditions. Thereby, the overall efficiency of the PV energy production system is increased. Numerous techniques have been presented during the last decades for implementing the MPPT process in a PV system. This chapter provides an overview of the operating principles of these techniques, which are suited for either uniform or nonuniform solar irradiation conditions. The operational characteristics and implementation requirements of these MPPT methods are alsoanalyzed in order to demonstrate their performance features
Solar Power Sources:PV, Concentrated PV, and Concentrated Solar Power
No full textSolar power is highly abundant, relatively reliable, and not limited to a geographic region, making it one of the most important renewable energy sources. Catering for a clean and green energy system, solar energy will be an active player in the future mixed power grid that is also undergoing a significant change. Beyond this energy transition, the still declining cost of the solar technology has become an important driving force for more solar-powered systems. However, high penetration of solar-powered systems also brings technical challenges to the entire energy systems. In order to fully address those issues, the technological properties of solar power should be investigated. Thus, the basics of solar power technology will be introduced and discussed in this chapter
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