Controladores repetitivos aplicados a filtros ativos de potência sob variações de carga e de frequência da rede

This work presents the development and modification of techniques to reduce the effects of load variation and mains frequency deviation in repetitive controllers applied to active power filters. To minimize the effects of aperiodic signals resulting from the connection or disconnection of non-linear loads is developed a technique which recognizes linear and nonlinear loads, and operates to reset the controller only when the error due to the transition of considerable value, and the transition is from non-linear to linear load. An algorithm to adapt the gain of the repetitive controller, based on a sigmoid function adaptation, in order to minimize the effects caused by random noise in the measurement system is also used. This work also analyzes the effects of frequency variation and presents the main methods to cope with this situation. Some solutions are the change in the number of samples per period and the variation of the sampling rate. The first has the advantage of using linear design techniques and results in a time invariant system. The second method changes the sampling frequency and leads to a time variant system that demands a difficult analysis of stability. The proposed algorithms were tested using the methods of truncation of the number of samples and the method of changing the sampling rate of the system to compensate possible frequency variations of the grid. Experimental results are presented to validate the proposal.

Comparação do controle do inversor trifásico conectado à rede com filtro LCL considerando o amortecimento passivo e ativo

Distributed generation systems must fulfill standards specifications of current harmonics injected to the grid. In order to satisfy these grid requirements, passive filters are connected between inverter and grid. This work compares the characteristic response of the traditional inductive (L) filter with the inductive-capacitive-inductive (LCL) filter. It is shown that increasing the inductance L leads to a good ripple current suppression around the inverter switching frequency. The LCL filter provides better harmonic attenuation and reduces the filter size. The main drawback is the LCL filter impedance, which is characterized by a typical resonance peak, which must be damped to avoid instability. Passive or active techniques can be used to damp the LCL resonance. To address this issue, this dissertation presents a comparison of current control for PV grid-tied inverters with L filter and LCL filter and also discuss the use of active and passive damping for different regions of resonance frequency. From the mathematical models, a design methodology of the controllers was developed and the dynamic behavior of the system operating in closed loop was investigated. To validate the studies developed during this work, experimental results are presented using a three-phase 5kW experimental platform. The main components and their functions are discussed in this work. Experimental results are given to support the theoretical analysis and to illustrate the performance of grid-connected PV inverter system. It is shown that the resonant frequency of the system, and sampling frequency can be associated in order to calculate a critical frequency, below which is essential to perform the damping of the LCL filter. Also, the experimental results show that the active buffer per virtual resistor, although with a simple development, is effective to damp the resonance of the LCL filter and allow the system to operate stable within predetermined parameters.

Projeto, implementação e análise de um conversor CC-CC de alto ganho e alto rendimento para aplicações fotovoltaicas

In recent years the photovoltaic generation has had greater insertion in the energy mix of the most developed countries, growing at annual rates of over 30%. The pressure for the reduction of pollutant emissions, diversification of the energy mix and the drop in prices are the main factors driving this growth. Grid tied systems plays an important role in alleviating the energy crisis and diversification of energy sources. Among the grid tied systems, building integrated photovoltaic systems suffers from partial shading of the photovoltaic modules and consequently the energy yield is reduced. In such cases, classical forms of modules connection do not produce good results and new techniques have been developed to increase the amount of energy produced by a set of modules. In the parallel connection technique of photovoltaic modules, a high voltage gain DC-DC converter is required, which is relatively complex to build with high efficiency. The current-fed isolated converters explored in this work have some desirable characteristics for this type of application, such as: low input current ripple and input voltage ripple, high voltage gain, galvanic isolation, feature high power capacity and it achieve soft switching in a wide operating range. This study presents contributions to the study of a high gain and high efficiency DC-DC converter for use in a parallel system of photovoltaic generation, being possible the use in a microinverter or with central inverter. The main contributions of this work are: analysis of the active clamping circuit operation proposing that the clamp capacitor connection must be done on the negative node of the power supply to reduce the input current ripple and thus reduce the filter requirements; use of a voltage doubler in the output rectifier to reduce the number of components and to extend the gain of the converter; detailed study of the converter components in order to raise the efficiency; obtaining the AC equivalent model and control system design. As a result, a DC-DC converter with high gain, high efficiency and without electrolytic capacitors in the power stage was developed. In the final part of this work the DC-DC converter operation connected to an inverter is presented. Besides, the DC bus controller is designed and are implemented two maximum power point tracking algorithms. Experimental results of full system operation connected to an emulator and subsequently to a real photovoltaic module are also given.

Arquitetura para o desenvolvimento de unidades de medição fasorial sincronizada no monitoramento a nível de distribuição

This work presents a low cost architecture for development of synchronized phasor measurement units (PMU). The device is intended to be connected in the low voltage grid, which allows the monitoring of transmission and distribution networks. Developments of this project include a complete PMU, with instrumentation module for use in low voltage network, GPS module to provide the sync signal and time stamp for the measures, processing unit with the acquisition system, phasor estimation and formatting data according to the standard and finally, communication module for data transmission. For the development and evaluation of the performance of this PMU, it was developed a set of applications in LabVIEW environment with specific features that let analyze the behavior of the measures and identify the sources of error of the PMU, as well as to apply all the tests proposed by the standard. The first application, useful for the development of instrumentation, consists of a function generator integrated with an oscilloscope, which allows the generation and acquisition of signals synchronously, in addition to the handling of samples. The second and main, is the test platform, with capabality of generating all tests provided by the synchronized phasor measurement standard IEEE C37.118.1, allowing store data or make the analysis of the measurements in real time. Finally, a third application was developed to evaluate the results of the tests and generate calibration curves to adjust the PMU. The results include all the tests proposed by synchrophasors standard and an additional test that evaluates the impact of noise. Moreover, through two prototypes connected to the electrical installation of consumers in same distribution circuit, it was obtained monitoring records that allowed the identification of loads in consumer and power quality analysis, beyond the event detection at the distribution and transmission levels.

Abundância e distribuição sazonal de espécies autóctones de camarões peneídeos no canal de abastecimento do sistema primar de aquicultura orgânica (Laguna de Guaraíras, Tibau do Sul, Rio Grande do Norte, Brasil)

Guaraíras lagoon, located in Tibau do Sul in the eastern littoral of Rio Grande do Norte (Brazil), presents a permanent connection to the sea, which guarantees the occurrence of a rich biodiversity, which includes the autochthonous shrimp species Litopenaeus schmitti, Farfantepenaeus subtilis and Farfantepenaeus brasiliensis. In spite of being subject to a strong human intervention in the last decade, mainly related to the installation of shrimp (Litopenaeus vannamei) farms, the lagoon is still scarcely studied. The present study aims at characterizing the populations of the three autochthonous penaeid shrimp species inhabiting Guaraíras, taking into consideration their abundance and seasonal distribution in the inflow channel of Primar System of Organic Aquaculture (Tibau do Sul, Rio Grande do Norte, Brazil). Twelve monthly samples were carried out from May 2005 to April 2006 with the aid of a circular cast net in the inflow channel, which is daily supplied with water from Guaraíras. Sampling months were grouped in trimesters according to the total pluviosity, thus comprising four trimesters. Water salinity was monitored twice a week and temperature values registered on a daily basis at noon, during the study period. The daily pluviosity data from the municipality of Tibau do Sul were supplied by Empresa de Pesquisa Agropecuária do Rio Grande do Norte (EMPARN). Collected shrimp were identified, weighted, measured and sexed. L. schmitti specimens (0.2 g to 17.8 g) were distributed in 1.3 g weight classes intervals. From the eighth sampling month (December 2005) onwards, males were classified into three categories, in accordance with the development of their petasm: (a) rudimentary petasm, (b) partially formed petasm, and (c) completely formed petasm. Among the ecological variables, rainfall showed the greatest dispersion (s.d.=187.74Rainfall and abundance of L. schmitti were negatively correlated (r = -0.85) whereas its abundance and water salinity were positively correlated (r = 0.63). Among 1,144 collected individuals, 1,127 were L. schmitti, 13 were F. subtilis and 4 were F. brasiliensis, which corresponded to 98.51%, 1.14% and 0.35% of the total of collected individuals. L. schmitti occurred in 100 % of all samples. Differently, the presence of F. subtilis and F. brasiliensis was restricted to 33% and 17% of the collected samples, respectively. The present study confirmed the occurrence of L. schmitti, F. brasiliensis and F. subtilis in Guaraíras. However, this lagoon seems to be primarily inhabited by juvenile Litopenaeus schmitti. The population of L. schmitti analysed showed a seasonal pattern of distribution. In general, in the months of high salinity and absence of rain, the number of individuals was higher than in the wet months. Further studies on the reproductive biology and ecology of L. schmitti, F. brasiliensis and F. subtilis may elucidate questions referring to the abundance, period, and phase of occurrence of these shrimp genera in Guaraíras. Finally, the risks associated to the establishment of L. vannamei in the lagoon provide a novel outlet for studies in this biotope

Estudo numérico experimental de treliças espaciais feitas com tubos de aço com ponta amassada e espaçadores de madeira para corrigir as excentricidades nos nós de ligação

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, 2015.

Caracterização ecológica dos peixes recifais do Atol das Rocas

The present work was carried out at the Atol das Rocas (3º 51 S; 33º 49 W), the only atoll of the South Atlantic and the first Brazilian marine protected area. It was guided by the following hypothesis: the composition of the fish communities varies in agreement with the position of the pools; in other words, with or without permanent ocean connection. To test the validity of this hypothesis, the fish abundance was estimated in the connected pools (Barretinha/Barreta Falsa) and unconnected ones (Cemiteriozinho/Âncoras), carrying an ecological characterization of the fishes that inhabit these pools. Additionally, the structural complexity of the sampled places was also evaluated intending to verify the variations of the abundance and diversity of fishes in function to this factor. By the fact of this research was being carried out through the limits of a conservation unit, the samples was realized using visual census techniques. The results generated through uni and multivariate analytic techniques allowed the evidence that decisive factor in the density, richness and diversity variations of fishes are linked to the substratum type (Hard / Soft bottom) and not by the fact that the pool are or are not connected permanently to the ocean. In relation to the structural complexity; 58% of the variations in the diversity of fishes were attributed to changes in the structural complexity, while 12% of the variations in the abundance were attributed to the structural complexity

Osteointegração nos amputados: um passo em frente!

ntrodução: Em Portugal, até agora, as próteses de reabilitação usadas para doentes amputados a nível transfemoral e transtibial condicionam trocas frequentes por motivos de alargamento, instabilidade, desconforto, problemas de pele e dor no coto que originam limitação funcional e perda de qualidade de vida. Em 1990, na Suécia, adoptou-se a técnica de osteointegração no membro inferior e superior com o desenvolvimento inovador da fixação óssea da prótese, eliminando o contacto com a pele e permitindo ganhar função e independência destes doentes. O desenvolvimento do protocolo OPRA permitiu definir critérios de indicação e seleção dos doentes e programar um processo de reabilitação individualizado. A técnica engloba 2 tempos cirúrgicos nos ossos longos. Os autores reportam o primeiro caso clínico de osteointegração realizado em Portugal. Caso Clínico: Um amputado transtibial com necessidade de trocas frequentes da prótese de reabilitação tipo socket, foi selecionado para osteointegração. Na fase S1 foi introduzido o implante intramedular. Após 6 meses, na fase S2 foi colocada a conexão de titânio por protusão à pele, e estabilização dos tecidos moles. O programa de reabilitação foi gradual e individualizado. Recorreu-se à escala visual analógica da dor para progressão da recuperação funcional. O doente está satisfeito e com capacidade de realizar eficazmente atividades até aqui inatingíveis. Discussão: A osteointegração implica uma equipa multidisciplinar e visa promover qualidade de vida e recuperar eficazmente doentes amputados para a sociedade ativa. Neste primeiro doente verificou-se ganho de função e independência com claro impacto psicosocioeconómico. Factores como a estrutura, dinâmica e bioquímica do tecido ósseo assim como a estabilização dos tecidos moles são fundamentais. As complicações possíveis incluem infeção, necrose cutânea, descelagem e fractura. As vantagens biomecânicas são maior segurança, suporte dos tecidos moles, estabilidade protésica e, no caso das amputações transfemorais, maior flexão do joelho. Conclusão: A osteointegração representa um passo em frente na reabilitação dos amputados e os autores acreditam que contribuirá no futuro para dotar as próteses de função sensitivomotora artificial, com o desenvolvimento das neurociências, robótica e engenharias electrotécnica e biomédica. A osteointegração permitiu projetar uma vida diferente e mais ativa para este doente, conjugando os impactos biomecânico, fisiológico, psicológico, social e económico.

Teoria da arte hacker : estética, diferença e transgressão tecnológica

Tese (doutorado)—Universidade de Brasília, Instituto de Artes, Departamento de Artes Visuais, Programa de Pós-Graduação em Arte, 2015.

Avaliação do efeito citotóxico da lectina da esponja marinha Cliona varians contra células de leucemia mielóide crônica

In this study, a BCR-ABL expressing human chronic myelogenous leukaemia cell line (K562) was used to investigate the antitumoral potential of a novel lectin (CvL) purified from the marine sponge Cliona varians. CvL inhibited the growth of K562 cells with an IC50 value of 70 g/ml, but was ineffective to normal human peripheral blood lymphocytes in the same range of concentrations tested (180 g/ml). Cell death occurred after 72 h of exposure to the lectin and with sign of apoptosis as analysed by DAPI staining. Investigation of the possible effectors of this process showed that cell death occurred in the presence of Bcl-2 and Bax expression, and involved a caspase-independent pathway. Confocal fluorescence microscopy indicated a major role for the lysosomal protease cathepsin B in mediating cell death. Accordingly, pre-incubation of K562 cells with the cathepsin inhibitor L-trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane (E-64) abolished the cytotoxic effect of CvL. Furthermore, we found upregulation of tumor necrosis factor receptor 1 (TNFR1) and down-modulation of p65 subunit of nuclear factor kappa B (NFB) expression in CvL-treated cells. These effects were accompanied by increased levels of p21 and downmodulation of pRb, suggesting that CvL is capable of cell cycle arrest. Collectively, these findings suggest that cathepsin B acts as death mediator in CvL-induced cytotoxicity possibly in a still uncharacterized connection with the membrane death receptor pathway

A motivação no processo educativo: relação entre os interesses e a aprendizagem da criança

Relatório de estágio apresentado à Escola Superior de Educação de Paula Frassinetti para obtenção de grau de Mestre em Educação Pré-Escolar e Ensino do 1º Ciclo do Ensino Básico

Desenvolvimento de uma bancada para a realização de ensaios de auto-amortecimento em cabos condutores de energia elétrica

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2015.

Continuidade do desempenho do cargo de diretor de turma e o impacto no sucesso educativo dos alunos: um estudo no 2º Ciclo de uma escola pública da Ilha da Madeira

A escola portuguesa do século XXI tem sido alvo de reformas sucessivas procedentes de imposições económicas, políticas e sociais, sem o devido acompanhamento de inovação bottom up. A mudança decorrente tem-se processado sobretudo formalmente (inovação top down), menosprezando, ainda em larga escala, as pessoas e o seu capital (intelectual, emocional, social e psicológico), num momento em que a globalização impulsiona a transição do paradigma funcional para o paradigma das competências. Sendo os indivíduos parte integrante das soluções e êxitos organizacionais, bem como cada vez mais manifesta a preocupação dos líderes com a eficácia, eficiência e qualidade do serviço prestado ao nível das escolas de interesse público, direcionamos a análise para a gestão dos recursos humanos, mais particularmente ao nível da dualidade: instabilidade na carreira docente/estabilidade do diretor de turma. O interesse supremo da temática reside nas potencialidades deste cargo de gestão intermédia na concretização da missão da escola, a partir do papel que o seu detentor assume na teia de relações em que se insere por imposição das suas funções, e que pode fomentar quando dotado de determinadas características. Este estudo de caso, de natureza essencialmente quantitativa, traduz a análise crítica acerca do impacto da continuidade do desempenho do cargo ao longo do 2.º ciclo do ensino básico no sucesso educativo dos alunos, partindo da análise dos resultados de medidas adotadas no ano escolar 2010/2011. Para o efeito recorreu-se à análise do aproveitamento, da atuação do conselho de turma e da comunicação escola-família em seis turmas do sexto ano de escolaridade, três com o mesmo diretor de turma, de uma escola pública do concelho de Câmara de Lobos. Concluímos que a manutenção do diretor de turma nas turmas visadas teve repercussões na vertente relacional, principalmente, não tendo sido confirmada a conexão entre a continuidade do profissional que assume o cargo ao longo do ciclo e os resultados académicos dos discentes, pese embora a opinião contrária de 87,9% dos docentes inquiridos, e de a maioria quer dos estudantes, quer dos seus encarregados de educação, ser favorável à sua prossecução.

A relação escola-família como potenciadora do sucesso educativo

Relatório de estágio apresentado à Escola Superior de Educação de Paula Frassinetti para obtenção de grau de Mestre em Educação Pré-Escolar e Ensino do 1º Ciclo do Ensino Básico

Características que podem influenciar a revisitação a um canal do YouTube

Atualmente, encontramo-nos numa Era em que a internet se está a transformar numa ferramenta cada vez mais essencial no nosso dia-a-dia. A internet, mais especificamente, as redes sociais apareceram para que o consumidor esteja em permanente conexão com o mundo, à distância de um clique. Nesta investigação, o YouTube foi a rede social escolhida para o estudo e o objetivo principal é perceber quais as características que um canal no YouTube deve ter para que os consumidores tenham intenção de o revisitar. Na metodologia adaptou-se um modelo que avalia a qualidade de websites, o modelo WebQual. Foi elaborado um questionário online, sendo as perguntas adaptadas para um canal de YouTube. Para analisar as hipóteses do estudo, foi feita uma regressão linear múltipla. Foi então possível concluir que os constructos Utilidade, Facilidade de Uso, Entretenimento e Relação Complementar, influenciam a Intenção de Revisitar logo, pode-se dizer que o canal do YouTube estudado apresenta qualidade aos olhos dos consumidores.