Modeling and enhanced control of hybrid full bridge–half bridge MMCs for HVDC grid studies

Modular multilevel converters (MMCs) are expected to play an important role in future high voltage direct current (HVDC) grids. Moreover, advanced MMC topologies may include various submodule (SM) types. In this sense, the modeling of MMCs is paramount for HVDC grid studies. Detailed models of MMCs are cumbersome for electromagnetic transient (EMT) programs due to the high number of components and large simulation times. For this reason, simplified models that reduce the computation times while reproducing the dynamics of the MMCs are needed. However, up to now, the models already developed do not consider hybrid MMCs, which consist of different types of SMs. In this paper, a procedure to simulate MMCs having different SM topologies is proposed. First, the structure of hybrid MMCs and the modeling method is presented. Next, an enhanced procedure to compute the number of SMs to be inserted that takes into account the different behavior of full-bridge SMs (FB-SMs) and half-bridge submodules (HB-SMs) is proposed in order to improve the steady-state and dynamic response of hybrid MMCs. Finally, the MMC model and its control are validated by means of detailed PSCAD simulations for both steady-state and transients conditions (AC and DC faults)

Fibras elásticas oxitalânicas e fibras colágenas durante o processo de reparo na inibição experimental do óxido nítrico

PURPOSE: To evaluate the repair process in rats with experimentally induced arterial hypertension. This study aimed to evaluate lesions in the ventricular myocardium and the repair process during experimental hypertension induced by systemic blockage of nitric oxide using N-omega-nitro-L-arginine methyl ester hydrochloride (L-NAME). Nitric oxide is an endothelial vasorelaxing factor and is necessary for the maintenance of normal arterial pressure, and L-NAME is an analog and antagonist of L-arginine, the substrate of the nitric oxide synthase. MATERIALS AND METHODS: We used 26 normotensive young male Wistar rats belonging to several litters. Animals were treated with oral administration of L-NAME dissolved in water (75 mg/100 mL) for 43 days . Hearts were weighed and processed by routine methods. Special stains utilized were Gomori's trichrome (aniline blue), picrosirius red polarization to identify fibrillar collagen, alcian blue technique (pH 0.5 and pH 2.5) to identify glycosaminoglycans, periodic acid-Schiff technique (with and without amylases) to identify proteoglycans, and Weigert's resorcinol fuchsin solution (with and without oxone) to identify elastic fibers. RESULTS: The results showed significant elevation of the arterial pressure (POBJETIVO: Avaliar o processo de reparo em ratos submetidos à hipertensão arterial experimental. Avaliamos lesões miocárdicas ventriculares e processos de reparo durante a hipertensão arterial experimental induzida pelo bloqueio da síntese do óxido nítrico (ON) utilizando o Hidrocloreto de L-NAME. ON é um fator de relaxamento endotelial e é necessário para a manutenção da pressão arterial normal. L-NAME é um analogo e antagonista da L-Arginine que é o substrato da enzima óxido nítrico sintase. MATERIAL E MÉTODOS: Utilizamos 26 ratos Wistar normotensos jovens oriundos de diversas ninhadas. Os animais foram submetidos ao L-NAME (Hidrocloreto de Nw-nitro-L-arginina metil ester) por administração via oral em água durante 43 dias (concentração: 75 mg / 100 ml). Os corações foram pesados e processados por métodos de rotina. Colorações Especiais utilizadas foram Tricrômico de Gomori (azul de anilina), Picro-Sirious Red sob luz polarizada para identificar as fibras colágenas, Técnica do Alcian Blue (pH 0,5 e pH 2,5) para identificar as glicosaminoglicanas, Técnica do Ácido Periódico Schiff (com e sem amilase) para identificar as proteoglicanas e Resorcina Fucsina de Weigert's (com e sem oxona) para identificar as fibras elásticas. RESULTADOS: Os resultados demonstram elevação significativa da pressão arterial (

A detailed Auger electron spectroscopy study of the first stages of the growth of C60 thin films

In this work we take advantage of the large sensitivity and in-depth resolution of Auger electron spectroscopy to study in a detailed way the growth of C60 over different substrates, namely Cu(111), Si(100) and graphene. The ability of AES, as compared to more local probes like STM or AFM, to follow the process in a dynamical way, allows us to study the growth of C60 below and over one ML, including the change of C60 over either Si or Cu to the growth of C60 over a C60 film. We found that the growth proceeds always as layer by layer. This result shows that differences in diffusion barriers are not as important as one can think following the idea of diffusion by a jumping mechanism. We propose that the sticking coefficient, governed by the adsorption energy, is the responsible of the differences observed between Cu and Si. Our results also point out to a different charge transfer among fullerene molecules and these surfaces. The same result is suggested in the case of C60 over graphene, but in this case our conclusion comes from the variable temperature experiments.Fil: Vidal, Ricardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Ferron, Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentin

Growth, thermal desorption and low dose ion bombardment damage of C60 films deposited on Cu(111)

Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED) and Reflection Electron Energy Loss Spectrometry (REELS) were used to characterize the growth and thermal stability of C60 films deposited on Cu(111). By means of LEED we found that while C60 grows in an ordered fashion up to the first monolayer (ML) at room temperature (RT), it turns amorphous beyond that point. On the other hand, when the substrate temperature is kept at 450K films up to two ML with crystalline structure are obtained. For substrate temperatures beyond 570K thick films (more than 1 ML) do not grow at all. By using AES, we found that a thick C60 film starts to desorb at a temperature around 470K but the first monolayer remains stable up to temperatures as high as 900K. A monolayer with a better crystalline order is obtained after desorption than that growth with the substrate at RT or higher temperatures. When the substrate is heated at 970K, the first monolayer is not fully removed but the C60 molecular structure is altered or molecules break up into smaller pieces. The ion induced damage on C60 on Cu(111) films was studied for typical ions, incoming energies and irradiation doses used in Low Energy Ion Scattering (LEIS) experiments. The D-value of C(KLL) Auger spectra and the -plasmon of REELS, were monitored to characterize the damage caused to the film. We found that, at low doses ( 1014 ions/cm2), damage is only detectable for massive ions like Ar, but not for H and He in the 2-8 keV range.Fil: Bonetto, Fernando Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Materiales; ArgentinaFil: Vidal, Ricardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Física; ArgentinaFil: Quintero Riascos, Vanessa Alexandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Bonin, Claudio Julio. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Ferron, Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Materiales; Argentin

Les rapports entre les amateurs et les professionnels dans les sciences participatives basées sur Internet : une exploration de Foldit

Cette recherche explore les rapports entre les amateurs et les professionnels scientifiques dans Foldit, une expérience de science participative sur Internet. Foldit est un jeu vidéo en ligne qui permet aux participants de trouver la façon dont les protéines se plient. Amateurs et professionnels de la science ont traversé une longue route colorée de partenariats et de démarcations. À l'heure actuelle, cette démarche se voit complexifiée par un environnement numérique qui relève le phénomène de la participation et la montée de la figure de l'amateur, notamment dans la production de connaissance. Si cette participation sur la Toile est considérée, par certains courants de pensée, comme le germe d'une nouvelle économie voire d'une nouvelle société (Benkler, 2006 ; Bauwens, 2012b), elle est aussi dénoncée par l'approche critique du capitalisme informationnel, comme une sorte de travail immatériel non rémunéré soumis à des relations d'exploitation (Moulier Boutang, 2007 ; Pasquinelli, 2010). Dans ce contexte, ce mémoire propose une exploration des sciences participatives, afin d'examiner les rapports qui s'établissent entre les acteurs de ces expériences productrices de connaissance et de données immatérielles. Ces rapports s'expriment à travers les échanges qui se déroulent sur le site web Foldit. La méthodologie qualitative mise en oeuvre a été complétée par l'observation de terrain et les entretiens semi-structurés avec des participants-joueurs et des membres de l'équipe scientifique du jeu. Les rapports trouvés dans Foldit se révèlent contextualisés, performatifs et sont façonnés par les compétences mises en jeu par les acteurs. Des rapports d'asymétrie, de coopération et de négociation sont repérés dans Foldit. Cette recherche veut contribuer ainsi à une meilleure compréhension des collectifs présents sur Internet ainsi que des rapports établis entre eux.This project explores the relationships between amateur and professional scientists within Foldit, a participatory science project on the Internet. Foldit is an online game in which participants fold proteins in novel ways. The long history of cooperation and differentiation between amateurs and professionals in science is becoming increasingly complex in digital environments as « amateur » participation gains in importance and is channelled by Web-based platforms, notably in the production of knowledge. While participation on the Web is considered by some as providing the seeds of a new economy or even a new society (Benkler, 2006; Bauwens, 2012b), others associated with a critical approach to informational capitalism, decry this type of participation as unpaid immaterial labour, carried out in a relation of exploitation (Moulier Boutang, 2007; Pasquinelli, 2010). In this context, my thesis proposes an exploration of participatory science, with a view to examining the relationships that develop between the different actors involved in these knowledge - and data - production exercises. We identify these relationships between the members through analysis of the exchanges that they produce on the site. This qualitative research also draws on observation, and semi-structured interviews with both amateur players and members of the Foldit team. We conclude by proposing a performative view of the development of relationships in Foldit, which prove to be highly dependent upon contextual factors and shaped to a large extent by the skills of the various actors. In the particular context of the New Chapter, negotiations are marked by both asymmetry and cooperation. This research helps develop a better understanding of the development and maintenance of relationships in online collectives

Light with tunable non-Markovian phase imprint

We introduce a simple and flexible method to generate spatially non-Markovian light with tunable coherence properties in one and two dimensions. The unusual behavior of this light is demonstrated experimentally by probing the far field and recording its diffraction pattern after a double slit: In both cases we observe instead of a central intensity maximum a line or cross shaped dark region, whose width and profile depend on the non-Markovian coherence properties. Since these properties can be controlled and easily reproduced in experiment, the presented approach lends itself to serve as a testbed to gain a deeper understanding of non-Markovian processes

Robust local controllers design for the AC grid voltage control of an offshore wind farm

Ponencia presentada en IFAC PapersOnLine 53-2 (2020) 12751–12756In this paper we deal with the problem of voltage control of the AC grid in an offshore wind farm by means of several converters, all of them connected to the AC offshore grid at the Point of Common Coupling (PCC) through different transmission lines. We propose to control the voltage simultaneously by all the connected converters, i.e., we have multiple actuators with the same goal. However, the number of operative converters can change during the wind farm operation and dynamics changes. Thus, it is necessary to assure the stability of the whole system in all different scenarios. In order to achieve a global design and implementation strategy, we propose the use of same controller parameters for all converters. For this kind of wind farm topology, we address the design of controllers as an optimization problem where we seek to maximize the robustness against uncertainty in the model of transmission lines and changes in the number of connected wind turbines guaranteeing the stability of the whole system in all different scenarios as well as a given settling time. Due to the proposed design strategy it is not necessary communication between different converters and controllers do not need to be re-tuned when the number of connected converters changes

Estudo empírico sobre a aplicação de uma estratégia de investimento com modelos de "Valuation" relativo para o Brasil período 01/2007 a 08/2009

A estratégia de avaliação de empresas por valor relativo é um importante método de escolha de portfólios de investimento no mercado financeiro. Este método é utilizado principalmente devido a sua praticidade e intuitividade da lógica de investimento. O objetivo do presente trabalho é avaliar a performance de uma estratégia de investimentos long/short utilizando-se de múltiplos para pares de empresas de um mesmo setor, que compra ativos considerados baratos e vende ativos considerado caros, avaliados desta forma caso a diferença entre os múltiplos superasse uma margem de segurança preestabelecida. A base de dados utilizada consiste na série diária de preços e múltiplos disponíveis na plataforma Bloomberg de 20 empresas e 10 setores sendo utilizada duas empresas de cada setor entre janeiro/2007 e Agosto/2009. Os setores foram escolhidos discricionariamente entre os mais importantes que apresentam ao menos duas empresas listadas na BMF&Bovespa. A conclusão principal reside no indício de que foi possível obter retornos positivos a qualquer benchmark, utilizando-se de tal estratégia durante o período. Esta conclusão é corroborada por duas análises de robustez, uma, variando-se a margem de segurança utilizada, e a outra analisando a performance do modelo, seccionando o período analisado em fases de propensão à risco alta e baixa. Nesta segunda análise, dividiu-se o período de janeiro de 2007 a Agosto de 2009 em três períodos bastante distintos. O primeiro entre janeiro de 2007 e agosto de 2008, caracterizado por boa performance de ativos de risco e valorização do Ibovespa, o segundo entre setembro de 2008 e novembro de 2008, caracterizado por forte busca por liquidez e desvalorização do Ibovespa de mais de 50%, e o último por uma forte reflação dos ativos de risco e retorno a tendência de valorização das ações brasileiras. O modelo obteve desempenho satisfatório em todos os períodos analisados