Power converter topologies for wind energy conversion systems: Integrated modeling, control strategy and performance simulation

This paper presents new integrated model for variable-speed wind energy conversion systems, considering a more accurate dynamic of the wind turbine, rotor, generator, power converter and filter. Pulse width modulation by space vector modulation associated with sliding mode is used for controlling the power converters. Also, power factor control is introduced at the output of the power converters. Comprehensive performance simulation studies are carried out with matrix, two-level and multilevel power converter topologies in order to adequately assert the system performance. Conclusions are duly drawn.

Human cryptosporidiosis: detection of specific antibodies in the serum by an indirect immunofluorescence

Cryptosporidium sp., a coccidian parasite usually found in the faeces of cattle, has been recently implicated as an agent of human intestinal disease, mainly in immunocompromised patients. In the study realized, by an indirect immunofluorescence technique, specific immunoglobulins (IgG and IgM) have been demonstrated in human serum against Cryptosporidium oocysts. Purified oocysts were used as antigens in the indirect immunofluorecence assay. After analyzing this test in sera from selected groups of patients, the frequency of both specific IgG and IgM of immunocompetent children who were excreting oocysts in their faeces was 62% and in children with negative excretion of oocysts was 20% and 40%, respectively. In adults infected with the human immunodeficiency virus (HIV) and who were excreting Cryptosporidium in their stools, the frequency was 57% for IgG but only 2% for IgM. Twenty three percent of immunocompromised adults with not determined excretion of oocysts in their stools had anti-Cryptosporidium IgG in their sera. Children infected with human immunodeficiency virus had no IgM and only 14% had IgG detectable in their sera. The indirect immunoflorescence assay, when used with other parasitological techniques appears to be useful for retrospective population studies and for diagnosis of acute infection. The humoral immune response of HIV positive patients to this protozoan agent needs clarification.

Reabilitação térmica e energética de edifício antigo: aplicação ao antigo edifício dos CTT em Coruche

O estudo desenvolvido no presente documento teve como alvo um edifício antigo construído entre 1930 e 1940 no concelho de Coruche, com construção característica da sua época. Numa fase inicial analisou-se de que forma se comporta o edifício em termos térmicos e energéticos, com base nas metodologias de cálculo apresentadas pelo regulamento térmico em vigor (RCCTE, 2006), e de seguida foram analisadas várias soluções existentes para a reabilitação térmica e energética do edifício que poderá ser concretizada, essencialmente devido às soluções para isolamento térmico das paredes, pavimentos e cobertura, assim como devido às soluções para vidros e caixilharia dos vãos envidraçados. Numa fase posterior, foi estudada a aplicação isolada das várias soluções de reabilitação consideradas, tendo sido simulada a aplicação de várias espessuras de isolante para as soluções da envolvente opaca e vários tipos de vidro duplo e caixilharia para as soluções da envolvente envidraçada, de forma a perceber-se a implicação que cada uma tem quanto à variação das necessidades energéticas do edifício. Por fim, foram calculados os custos de aplicação das várias soluções estudadas, com auxílio de um software de orçamentação, de forma que estas possam ser comparadas em termos da relação custo/benefício, em que, o benefício de cada solução será a variação provocada nas necessidades energéticas do edifício com aplicação da mesma. Assim, procurará encontrar-se para o edifício em estudo não só as soluções mais vantajosas em termos energéticos mas também as mais rentáveis, e procurará perceber-se se um investimento numa intervenção de reabilitação deste género conduzirá a um período de retorno do investimento reduzido, que possa ser considerado aceitável.

Estratégias para negociação de contratos bilaterais em mercados multi-agente de energia eléctrica

A energia eléctrica é um bem essencial para a maioria das sociedades. O seu fornecimento tem sido encarado como um serviço público, da responsabilidade dos governos, através de empresas monopolistas, públicas e privadas. O Mercado Ibérico de Electricidade (MIBEL) surge com o objectivo da integração e cooperação do sector eléctrico Português e Espanhol, no qual é possível negociar preços e volumes de energia. Actualmente, as entidades podem negociar através de um mercado bolsista ou num mercado de contratos bilaterais. Uma análise dos mercados de electricidade existentes mostra que estes estão longe de estarem liberalizados. As tarifas não reflectem o efeito da competitividade. Além disso, o recurso a contratos bilaterais limita frequentemente os clientes a um único fornecedor de energia eléctrica. Nos últimos anos, têm surgido uma série de ferramentas computacionais que permitem simular, parte ou a totalidade, dos mercados de electricidade. Contudo, apesar das suas potencialidades, muitos simuladores carecem de flexibilidade e generalidade. Nesta perspectiva, esta dissertação tem como principal objectivo o desenvolvimento de um simulador de mercados de energia eléctrica que possibilite lidar com as dificuldades inerentes a este novo modelo de mercado, recorrendo a agentes computacionais autónomos. A dissertação descreve o desenho e a implementação de um simulador simplificado para negociação de contratos bilaterais em mercados de energia, com particular incidência para o desenho das estratégias a utilizar pelas partes negociais. Além disso, efectua-se a descrição de um caso prático, com dados do MIBEL. Descrevem-se também várias simulações computacionais, envolvendo retalhistas e consumidores de energia eléctrica, que utilizam diferentes estratégias negociais. Efectua-se a análise detalhada dos resultados obtidos. De forma sucinta, os resultados permitem concluir que as melhores estratégias para cada entidade, no caso prático estudado, são: a estratégia de concessões fixas, para o retalhista, e a estratégia de concessões baseada no volume de energia, para o consumidor.

Conservação, manutenção e construção de património estratégico das águas de Santarém

A água é um bem essencial ao ser humano. Nos dias de hoje é de extrema importância fazer chegar este bem às populações, um papel que no nosso país é desempenhado pelos municípios, por empresas municipais e por empresas concessionadas. Este relatório, enquadrado no âmbito do trabalho final de mestrado em Engenharia Civil, especialização em Hidráulica, no Instituto Superior de Engenharia de Lisboa, cujo título é “Conservação, Manutenção e Construção de Património Estratégico das Águas de Santarém”, relata a experiência de estágio do autor do presente relatório na A.S. – Empresa das Águas de Santarém – EM, S.A. O relatório aborda as temáticas do abastecimento de água, do tratamento de águas residuais, da construção de sistemas de saneamento e estações de tratamento de águas residuais, da reparação de equipamentos da empresa e do consumo de energia dos equipamentos da empresa. São descritas as actividades desenvolvidas pelo autor, que incluem o acompanhamento activo em visitas a obras de construção e manutenção de património, a monitorização e controlo de perdas de água, bem como a actualização em suporte informático do cadastro dos equipamentos pertencentes à A.S., com a criação de fichas de equipamento individuais e de um suporte informático para registo e consulta comparativa de consumos energéticos. Esta experiência de estágio permitiu ao autor um contacto com a realidade de uma empresa em toda a diversidade das actividades anteriormente nomeadas, que será descrita objectivamente nos capítulos do presente documento. O estágio foi claramente enriquecedor para o autor, fornecendo-lhe formação objectiva e a preparação necessária para a sua integração no mercado de trabalho nesta área específica da Engenharia Civil.

Fractional-order control and simulation of wind energy systems with PMSG/full-power converter topology

This paper presents a new integrated model for the simulation of wind energy systems. The proposed model is more realistic and accurate, considering a variable-speed wind turbine, two-mass rotor, permanent magnet synchronous generator (PMSG), different power converter topologies, and filters. Additionally, a new control strategy is proposed for the variable-speed operation of wind turbines with PMSG/full-power converter topology, based on fractional-order controllers. Comprehensive simulation studies are carried out with matrix and multilevel power converter topologies, in order to adequately assert the system performance in what regards the quality of the energy injected into the electric grid. Finally, conclusions are duly drawn.

Light pollution and energy efficiency: a case study of the village of Vialonga

Since industrialization and the formation of larger urban centers in the nineteenth century, pollution of the environment was always present in daily life in various ways, namely in the form of light. Light pollution can cause various consequences, both for humans and for their ecosystem, producing effects on environmental, social, economic and scientific level. In Portugal, the lighting is responsible for 3% of total electricity consumption, energy costs are in some cases more than 50% towards the costs incurred by municipalities with energy, checking-in recent years a trend similar to that improvement of illumination levels in the region (about 4 to 5% per year). Proper use of lighting brings many benefits both to the citizen and environment, since greater energy efficiency can contribute to reducing CO2 emissions, energy costs, as well as to decrease the use of resources not-renewable and/or contamination of renewable resources, which can occurs in the process of obtaining electricity. The present study has a main goal to analyze the illuminance levels associated to the public lighting of the village of Vialonga, Vila Franca de Xira (Portugal), to verify if it is efficient. The aim is also to relate the efficiency of street lighting with the existence of light pollution.

Effect of the number of shells on the pressure and energy of two-dimensional free bubble clusters

We have performed Surface Evolver simulations of two-dimensional hexagonal bubble clusters consisting of a central bubble of area lambda surrounded by s shells or layers of bubbles of unit area. Clusters of up to twenty layers have been simulated, with lambda varying between 0.01 and 100. In monodisperse clusters (i.e., for lambda = 1) [M.A. Fortes, F Morgan, M. Fatima Vaz, Philos. Mag. Lett. 87 (2007) 561] both the average pressure of the entire Cluster and the pressure in the central bubble are decreasing functions of s and approach 0.9306 for very large s, which is the pressure in a bubble of an infinite monodisperse honeycomb foam. Here we address the effect of changing the central bubble area lambda. For small lambda the pressure in the central bubble and the average pressure were both found to decrease with s, as in monodisperse clusters. However, for large,, the pressure in the central bubble and the average pressure increase with s. The average pressure of large clusters was found to be independent of lambda and to approach 0.9306 asymptotically. We have also determined the cluster surface energies given by the equation of equilibrium for the total energy in terms of the area and the pressure in each bubble. When the pressures in the bubbles are not available, an approximate equation derived by Vaz et al. [M. Fatima Vaz, M.A. Fortes, F. Graner, Philos. Mag. Lett. 82 (2002) 575] was shown to provide good estimations for the cluster energy provided the bubble area distribution is narrow. This approach does not take cluster topology into account. Using this approximate equation, we find a good correlation between Surface Evolver Simulations and the estimated Values of energies and pressures. (C) 2008 Elsevier B.V. All rights reserved.

Eastwards / westwards: which direction for gender studies in the 21st century?

Eastwards / Westwards: Which Direction for Gender Studies in the XXIst Century? is a collection of essays which focus on themes and methods that characterize current research into gender in Asian countries in general. In this collection, ideas derived from Gender Studies elsewhere in the world have been subjected to scrutiny for their utility in helping to describe and understand regional phenomena. But the concepts of Local and Global – with their discoursive productions – have not functioned as a binary opposition: localism and globalism are mutually constitutive and researchers have interrogated those spaces of interaction between the ‘self’ and the ‘other’, bearing in mind their own embeddedness in social and cultural structures and their own historical memory. Contributors to this collection provided a critical transnational perspective on some of the complex effects of the dynamics of cultural globalization, by exploring the relation between gender and development, language, historiography, education and culture. We have also given attention to the ideological and rhetorical processes through which gender identity is constructed, by comparing textual grids and patterns of expectation. Likewise, we have discussed the role of ethnography, anthropology, historiography, sociology, fiction, popular culture and colonial and post-colonial sources in (re)inventing old/new male/female identities, their conversion into concepts and circulation through time and space. This multicultural and trans-disciplinary selection of essays is totally written in English, fully edited and revised, therefore, it has a good potential for an immediate international circulation. This project may trace new paths and issues for discussion on what concerns the life, practices and narratives by and about women in Asia, as well as elsewhere in the present day global experience. Academic readership: Researchers, scholars, educators, graduate and post-graduate students, doctoral students and general non-fiction readers, with a special interest in Gender Studies, Asia, Colonial and Post-Colonial Literature, Anthropology, Cultural Studies, History, Historiography, Politics, Race, Feminism, Language, Linguistics, Power, Political and Feminist Agendas, Popular Culture, Education, Women’s Writing, Religion, Multiculturalism, Globalisation, Migration. Chapter summary: 1. “Social Gender Stereotypes and their Implication in Hindi”, Anjali Pande, Jawaharlal Nehru University, New Delhi, India. This essay looks at the subtle ways in which gender identities are constructed and reinforced in India through social norms of language use. Language itself becomes a medium for perpetuating gender stereotypes, forcing its speakers to confirm to socially defined gender roles. Using examples from a classroom discussion about a film, this essay will highlight the underlying rigid male-female stereotypes in Indian society with their more obvious expressions in language. For the urban woman in India globalisation meant increased economic equality and exposure to changed lifestyles. On an individual level it also meant redefining gender relations and changing the hierarchy in man-­woman relationships. With the economic independence there is a heightened sense of liberation in all spheres of social life, a confidence to fuzz the rigid boundaries of gender roles. With the new films and media celebrating this liberated woman, who is ready to assert her sexual needs, who is ready to explode those long held notions of morality, one would expect that the changes are not just superficial. But as it soon became obvious in the course of a classroom discussion about relationships and stereotypes related to age, the surface changes can not become part of the common vocabulary, for the obvious reason that there is still a vast gap between the screen image of this new woman and the ground reality. Social considerations define the limits of this assertiveness of women, whereas men are happy to be liberal within the larger frame of social sanctions. The educated urban woman in India speaks in favour of change and the educated urban male supports her, but one just needs to scratch the surface to see the time tested formulae of gender roles firmly in place. The way the urban woman happily balances this emerging promise of independence with her gendered social identity, makes it necessary to rethink some aspects of looking at gender in a gradually changing, traditional society like India. 2. “The Linguistic Dimension of Gender Equality”, Alissa Tolstokorova, Kiev Centre for Gender Information and Education, Ukraine. The subject-matter of this essay is gender justice in language which, as I argue, may be achieved through the development of a gender-related approach to linguistic human rights. The last decades of the 20th century, globally marked by a “gender shift” in attitudes to language policy, gave impetus to the social movement for promoting linguistic gender equality. It was initiated in Western Europe and nowadays is moving eastwards, as ideas of gender democracy progress into developing countries. But, while in western societies gender discrimination through language, or linguistic sexism, was an issue of concern for over three decades, in developing countries efforts to promote gender justice in language are only in their infancy. My argument is that to promote gender justice in language internationally it is necessary to acknowledge the rights of women and men to equal representation of their gender in language and speech and, therefore, raise a question of linguistic rights of the sexes. My understanding is that the adoption of the Universal Declaration of Linguistic Rights in 1996 provided this opportunity to address the problem of gender justice in language as a human rights issue, specifically as a gender dimension of linguistic human rights. 3. “The Rebirth of an Old Language: Issues of Gender Equality in Kazakhstan”, Maria Helena Guimarães, Polytechnic Institute of Porto, Portugal. The existing language situation in Kazakhstan, while peaceful, is not without some tension. We propose to analyze here some questions we consider relevant in the frame of cultural globalization and gender equality, such as: free from Russian imperialism, could Kazakhstan become an easy prey of Turkey’s “imperialist dream”? Could these traditionally Muslim people be soon facing the end of religious tolerance and gender equality, becoming this new old language an easy instrument for the infiltration in the country of fundamentalism (it has already crossed the boarders of Uzbekistan), leading to a gradual deterioration of its rich multicultural relations? The present structure of the language is still very fragile: there are three main dialects and many academics defend the re-introduction of the Latin alphabet, thus enlarging the possibility of cultural “contamination” by making the transmission of fundamentalist ideas still easier through neighbour countries like Azerbaijan, Uzbekistan and Turkmenistan (their languages belong to the same sub-group of Common Turkic), where the Latin alphabet is already in use, and where the ground for such ideas shown itself very fruitful. 4. “Construction of Womanhood in the Bengali Language of Bangladesh”, Raasheed Mahmood; University of New South Wales, Sydney. The present essay attempts to explore the role of gender-based language differences and of certain markers that reveal the status accorded to women in Bangladesh. Discrimination against women, in its various forms, is endemic in communities and countries around the world, cutting across class, race, age, and religious and national boundaries. One cannot understand the problems of gender discrimination solely by referring to the relationship of power or authority between men and women. Rather one needs to consider the problem by relating it to the specific social formation in which the image of masculinity and femininity is constructed and reconstructed. Following such line of reasoning this essay will examine the nature of gender bias in the Bengali language of Bangladesh, holding the conviction that as a product of social reality language reflects the socio-cultural behaviour of the community who speaks it. This essay will also attempt to shed some light on the processes through which gender based language differences produce actual consequences for women, who become exposed to low self-esteem, depression and systematic exclusion from public discourse. 5. “Marriage in China as an expression of a changing society”, Elisabetta Rosado David, University of Porto, Portugal, and Università Ca’Foscari, Venezia, Italy. In 29 April 2001, the new Marriage Law was promulgated in China. The first law on marriage was proclaimed in 1950 with the objective of freeing women from the feudal matrimonial system. With the second law, in 1981, values and conditions that had been distorted by the Cultural Revolution were recovered. Twenty years later, a new reform was started, intending to update marriage in the view of the social and cultural changes that occurred with Deng Xiaoping’s “open policy”. But the legal reform is only the starting point for this case-study. The rituals that are followed in the wedding ceremony are often hard to understand and very difficult to standardize, especially because China is a vast country, densely populated and characterized by several ethnic minorities. Two key words emerge from this issue: syncretism and continuity. On this basis, we can understand tradition in a better way, and analyse whether or not marriage, as every social manifestation, has evolved in harmony with Chinese culture. 6. “The Other Woman in the Portuguese Colonial Empire: The Case of Portuguese India”, Maria de Deus Manso, University of Évora, Portugal. This essay researches the social, cultural and symbolic history of local women in the Portuguese Indian colonial enclaves. The normative Portuguese overseas history has not paid any attention to the “indigenous” female populations in colonial Portuguese territories, albeit the large social importance of these social segments largely used in matrimonial and even catholic missionary strategies. The first attempt to open fresh windows in the history of this new field was the publication of Charles Boxer’s referential study about Women in lberian Overseas Expansion, edited in Portugal only after the Revolution of 1975. After this research we can only quote some other fragmentary efforts. In fact, research about the social, cultural, religious, political and symbolic situation of women in the Portuguese colonial territories, from the XVI to the XX century, is still a minor historiographic field. In this essay we discuss this problem and we study colonial representations of women in the Portuguese Indian enclaves, mainly in the territory of Goa, using case studies methodologies. 7. “Heading East this Time: Critical Readings on Gender in Southeast Asia”, Clara Sarmento, Polytechnic Institute of Porto, Portugal. This essay intends to discuss some critical readings of fictional and theoretical texts on gender condition in Southeast Asian countries. Nowadays, many texts about women in Southeast Asia apply concepts of power in unusual areas. Traditional forms of gender hegemony have been replaced by other powerful, if somewhat more covert, forms. We will discuss some universal values concerning conventional female roles as well as the strategies used to recognize women in political fields traditionally characterized by male dominance. Female empowerment will mean different things at different times in history, as a result of culture, local geography and individual circumstances. Empowerment needs to be perceived as an individual attitude, but it also has to be facilitated at the macro­level by society and the State. Gender is very much at the heart of all these dynamics, strongly related to specificities of historical, cultural, ethnic and class situatedness, requiring an interdisciplinary transnational approach.

Solid-State Bipolar Marx Converter with Output Transformer and Energy Recovery

The purpose of this paper is to present and discuss a general HV topology of the solid-state Marx modulator, for unipolar or bipolar generation connected with a step-up transformer to increase the output voltage applied to a resistive load. Due to the use of an output transformer, discussion about the reset of the transformer is made to guarantee zero average voltage applied to the primary. It is also discussed the transformer magnetizing energy recovering back to the energy storage capacitors. Simulation results for a circuit that generates 100 kV pulses using 1000 V semiconductors are presented and discussed regarding the voltage and current stress on the semiconductors and result obtained.

A DC-DC Step-Up mu-Power Converter for Energy Harvesting Applications, Using Maximum Power PointTracking, Based on Fractional Open Circuit Voltage

A DC-DC step-up micro power converter for solar energy harvesting applications is presented. The circuit is based on a switched-capacitorvoltage tripler architecture with MOSFET capacitors, which results in an, area approximately eight times smaller than using MiM capacitors for the 0.131mu m CMOS technology. In order to compensate for the loss of efficiency, due to the larger parasitic capacitances, a charge reutilization scheme is employed. The circuit is self-clocked, using a phase controller designed specifically to work with an amorphous silicon solar cell, in order to obtain themaximum available power from the cell. This will be done by tracking its maximum power point (MPPT) using the fractional open circuit voltage method. Electrical simulations of the circuit, together with an equivalent electrical model of an amorphous silicon solar cell, show that the circuit can deliver apower of 1132 mu W to the load, corresponding to a maximum efficiency of 66.81%.

A risk-averse optimization model for trading wind energy in a market environment under uncertainty

In this paper, a stochastic programming approach is proposed for trading wind energy in a market environment under uncertainty. Uncertainty in the energy market prices is the main cause of high volatility of profits achieved by power producers. The volatile and intermittent nature of wind energy represents another source of uncertainty. Hence, each uncertain parameter is modeled by scenarios, where each scenario represents a plausible realization of the uncertain parameters with an associated occurrence probability. Also, an appropriate risk measurement is considered. The proposed approach is applied on a realistic case study, based on a wind farm in Portugal. Finally, conclusions are duly drawn. (C) 2011 Elsevier Ltd. All rights reserved.

A Step-up mu-Power Converter for Solar Energy Harvesting Applications, using Hill Climbing Maximum Power Point Tracking

This paper presents a step-up micro-power converter for solar energy harvesting applications. The circuit uses a SC voltage tripler architecture, controlled by an MPPT circuit based on the Hill Climbing algorithm. This circuit was designed in a 0.13 mu m CMOS technology in order to work with an a-Si PV cell. The circuit has a local power supply voltage, created using a scaled down SC voltage tripler, controlled by the same MPPT circuit, to make the circuit robust to load and illumination variations. The SC circuits use a combination of PMOS and NMOS transistors to reduce the occupied area. A charge re-use scheme is used to compensate the large parasitic capacitors associated to the MOS transistors. The simulation results show that the circuit can deliver a power of 1266 mu W to the load using 1712 mu W of power from the PV cell, corresponding to an efficiency as high as 73.91%. The simulations also show that the circuit is capable of starting up with only 19% of the maximum illumination level.

Data mining contributions to characterize MV consumers and to improve the suppliers-consumers settlements

This paper deals with the establishment of a characterization methodology of electric power profiles of medium voltage (MV) consumers. The characterization is supported on the data base knowledge discovery process (KDD). Data Mining techniques are used with the purpose of obtaining typical load profiles of MV customers and specific knowledge of their customers’ consumption habits. In order to form the different customers’ classes and to find a set of representative consumption patterns, a hierarchical clustering algorithm and a clustering ensemble combination approach (WEACS) are used. Taking into account the typical consumption profile of the class to which the customers belong, new tariff options were defined and new energy coefficients prices were proposed. Finally, and with the results obtained, the consequences that these will have in the interaction between customer and electric power suppliers are analyzed.

Short-term wind forecasting for energy resources scheduling

This paper proposes a wind power forecasting methodology based on two methods: direct wind power forecasting and wind speed forecasting in the first phase followed by wind power forecasting using turbines characteristics and the aforementioned wind speed forecast. The proposed forecasting methodology aims to support the operation in the scope of the intraday resources scheduling model, namely with a time horizon of 5 minutes. This intraday model supports distribution network operators in the short-term scheduling problem, in the smart grid context. A case study using a real database of 12 months recorded from a Portuguese wind power farm was used. The results show that the straightforward methodology can be applied in the intraday model with high wind speed and wind power accuracy. The wind power forecast direct method shows better performance than wind power forecast using turbine characteristics and wind speed forecast obtained in first phase.