Analytical calculation of resonant inductance for zero voltage switching in phase-shifted full-bridge converters

The phase shift full bridge (PSFB) converter allows high efficiency power conversion at high frequencies through zero voltage switching (ZVS); the parasitic drain-to-source capacitance of the MOSFET is discharged by a resonant inductance before the switch is gated resulting in near zero turn-on switching losses. Typically, an extra inductance is added to the leakage inductance of a transformer to form the resonant inductance necessary to charge and discharge the parasitic capacitances of the PSFB converter. However, many PSFB models do not consider the effects of the magnetizing inductance or dead-time in selecting the resonant inductance required to achieve ZVS. The choice of resonant inductance is crucial to the ZVS operation of the PSFB converter. Incorrectly sized resonant inductance will not achieve ZVS or will limit the load regulation ability of the converter. This paper presents a unique and accurate equation for calculating the resonant inductance required to achieve ZVS over a wide load range incorporating the effects of the magnetizing inductance and dead-time. The derived equations are validated against PSPICE simulations of a PSFB converter and extensive hardware experimentations.

An enhanced model for small-signal analysis of the phase-shifted full-bridge converter

This paper presents an in-depth critical discussion and derivation of a detailed small-signal analysis of the Phase-Shifted Full-Bridge (PSFB) converter. Circuit parasitics, resonant inductance and transformer turns ratio have all been taken into account in the evaluation of this topology’s open-loop control-to-output, line-to-output and load-to-output transfer functions. Accordingly, the significant impact of losses and resonant inductance on the converter’s transfer functions is highlighted. The enhanced dynamic model proposed in this paper enables the correct design of the converter compensator, including the effect of parasitics on the dynamic behavior of the PSFB converter. Detailed experimental results for a real-life 36V-to-14V/10A PSFB industrial application show excellent agreement with the predictions from the model proposed herein.1

Bond graph models of DC-DC converters operating in both CCM and DCM

In this paper, Bond Graphs are employed to develop a novel mathematical model of conventional switched-mode DC-DC converters valid for both continuous and discontinuous conduction modes. A unique causality bond graph model of hybrid models is suggested with the operation of the switch and the diode to be represented by a Modulated Transformer with a binary input and a resistor with fixed conductance causality. The operation of the diode is controlled using an if-then function within the model. The extracted hybrid model is implemented on a Boost and Buck converter with their operations to change from CCM to DCM and to return to CCM. The vector fields of the models show validity in a wide operation area and comparison with the simulation of the converters using PSPICE reveals high accuracy of the proposed model, with the Normalised Root Means Square Error and the Maximum Absolute Error remaining adequately low. The model is also experimentally tested on a Buck topology.

Magnetic Susceptibility Measurements at Ultra-low Temperatures

We report the design and operation of a device for ac magnetic susceptibility measurements that can operate down to 1 mK. The device, a modification of the standard mutual inductance bridge, is designed with detailed consideration of the thermalization and optimization of each element. First, in order to reduce local heating, the primary coil is made with superconducting wire. Second, a low-temperature transformer which is thermally anchored to the mixing chamber of a dilution refrigerator, is used to match the output of the secondary coil to a high-sensitivity bridge detector. The careful thermal anchoring of the secondary coil and the matching transformer is required to reduce the overall noise temperature and maximize sensitivity. The sample is immersed in liquid (3)He to minimize the Kapitza thermal resistance. The magnetic susceptibility of several magnetic compounds, such as the well-known spin gap compound NiCl(2)-4SC(NH(2))(2) and other powdered samples, have been successfully measured to temperatures well below 10 mK.

As relações de trabalho nas organizações de economia solidária : um paralelo Brasil-França

O objetivo desta pesquisa é o estudo das relações que se estabelecem entre o trabalhador e seu trabalho em organizações não convencionais, isto é, que não se identificam com o modo capitalista de produção e que reivindicam, pelo contrário, a criatividade e a originalidade de um trabalho mais autônomo, mais justo e mais responsável: a economia solidária. O que significa, para o trabalhador, atuar nestas organizações? É a pergunta que orienta este estudo. Dito de outro modo: a experiência vivida no trabalho cotidiano pelo trabalhador da economia solidária manifesta-se mediante práticas profissionais e práticas sociais reveladoras de novas formas de inserção no trabalho e na sociedade? Seria essa experiência fruto de uma transformação que ocorre em alguns segmentos do mundo do trabalho e observável em outros contextos econômicos ou um reflexo da situação particularmente fragilizada dos trabalhadores brasileiros? Tratar-se-á então de entender a singularidade da participação dos trabalhadores a este projeto, seu impacto sobre o desenvolvimento de seu trabalho e das relações estabelecidas com a organização e de estudar as transformações que podem ocorrer nas relações sociais a partir do trabalho. Este será analisado sob uma dimensão subjetiva, como experiência de construção identitária, e sob uma dimensão institucional, como socialização para e pela solidariedade. O conceito de “trabalho solidário”, que reúne essas dimensões, será analisado apoiando-se, em grande parte, na obra de François Dubet e sua teoria do ator, da estrutura social e da socialização. A pesquisa se inscreve numa perspectiva de contribuição à Sociologia do Trabalho e das relações de trabalho sem a pretensão de realizar uma sociologia da economia solidária, nas suas múltiplas relações com a sociedade. O que está em foco é a transformação das relações entre o trabalhador e seu trabalho. O argumento defendido pela pesquisa é que as relações que nascem de uma experiência cotidiana do trabalho nas organizações da economia solidária são peculiares e diversificadas, mas interpelam e desafiam o conjunto das relações sociais. Portanto, o trabalho realizado nessas organizações talvez seria, apesar de suas ambigüidades, suscetível de estimular novas formas de relações sociais por meio de uma socialização assentada na solidariedade. Três tipos de organizações “referências” (tipos ideais) são construídos a partir do tipo de produção dominante e dos valores e objetivos que motivam a ação: organizações de produção, associações culturais e organizações humanitárias. A comparação Brasil – França, através das organizações investigadas em Porto Alegre e Paris, procura homologias, isto é: correspondências na construção da ação apesar de contextos diferentes, assim como a reconstrução de processos e procura de especificidades que possam enriquecer as interações. No decorrer da investigação, o que se encontrou, tanto no Brasil quanto na França, foi de um lado, um discurso “oficial” (mentores, militantes da economia solidária e pesquisadores) que descreve a tarefa que se atribui a economia solidária: a responsabilização de todos para transformar a sociedade. Por outro lado, encontrou-se, através do discurso dos trabalhadores, o relato da realidade quotidiana que aparece como um mundo de tensões e contradições. Para entender essa aparente incompatibilidade, foi preciso recriar os mecanismos de construção do trabalho solidário: em que medida pode-se falar de experiência social e em que medida a socialização para e pela solidariedade é bem sucedida. Para tanto, foi necessário recompor o processo de construção das relações sociais dentro e fora do trabalho, manifestado mediante estratégias dos atores que precisam se posicionar frente às lógicas de ação desenvolvidas pelas organizações. A seguir, analisou-se a possibilidade de encontrar semelhanças e diferenças entre o Brasil e a França na construção deste trabalho solidário. Enfim, procurou-se responder à pergunta que originou esta pesquisa: seria mesmo o trabalho solidário gerador de novas relações sociais no trabalho e no âmbito mais amplo da sociedade?

Héritage et transmission des savoirs dans une communauté de pêcheurs portugaise

La pêche est une activité complexe qui fait appel aux sens, à la perception et à l'analyse, aboutissant à un savoir-faire qui est l’ensemble des comportements maîtrisés. Ce savoir s'acquiert par transmission, et par l'expérience que seule la pratique confère. On ne peut donc dissocier dans l'analyse l'apprentissage didactique de l'acquisition empirique. Longtemps les générations de pêcheurs se sont succédées les unes aux autres et rares étaient ceux dont le chemin s'écartait du modèle traditionnel. Depuis quelques années, et en raison de la défection de la jeunesse pour le métier, les aînés n'exercent plus leur activité de formateur. Pour ne pas interrompre la transmission de ce 'capital cognitif' qui permet à un groupe de se perpétuer comme de se transformer, et pour pallier le manque de formateurs, dû à la disparition des anciens, d'autres voies sont empruntées.

A Fogueira do conhecimento: religação de saberes e formação

Les récits sur les expériences de vie se constituent en apprentissages signifiants dans le processus d´ auto-formation des éducateurs. La formation est un phenomène qui extrapôle l ambiance scolaire, incluant les expériences qui servent de matrice pour la construction de la connaissance au long de la vie. Dans cette perspective, «la connaissance de soi», telle quelle proposée par SOUZA, NOVOA et JOSSO, est la notion centrale au tour de laquelle se développe cette dissertation. La recherche a comme idée principale transposer pour la realité des professeurs l´exercice reflexif de son enseignement, médiant la redécouverte de ses expériences de vie, a travers des histoires de soi que, potentialisés, peuvent transformer ses pratiques dans la classe scolaire. Je prends comme point de départ mes propres expériences comme éducatrice assumant la conviction de la indissociation entre sujet et objet de la connaissance, comme propose Édgar Morin pour parler de la science de la complexité. Je fais aussi l´usage des récits de six professeurs du réseau publique de l enseigment, révélateurs de la construction de la connaissance appuyée dans la cohérence de la praxis pédagogique avec son mode de comprendre et sentir le monde. Les oeuvres «Mes Démons» d Édgar Morin, «O Tempo e Eu» de Luis da Câmara Cascudo et «O Banquete dos Deuses» de Daniel Munduruku, ont élargit le champs des récits d expériences que se constituent en matrices des processus de formation. Le travail avec les récits de formation démontrent qu´à partir de la réflection du sujet sur sa propre expérience, il est possible de se projéter des nouvelles configurations de la connaissance tenant comme base, la reliaison entre vie, idées, et pratiques pédagogiques. À partir de la métaphore du bûcher il est possible de se comprendre la force de combustion des expériences de vie dans la formation des enseignants

Educar para a vida: uma pedagogia da resiliência na escola

Cet étude et thème de dissertation est devenue nécessaire a partir des inquiétudes d éducateur et des pratiques pédagogiques développées aux classes d éducation physique au tour nocturne à l École Municipale Prof. Veríssimo de Melo, dont les élèves sont des jeunes et adultes que habitent au quartier Felipe Camarão. Ces jeunes cohabitent avec le stigmate de la violence que est toujours présente dans cette communauté, située a la région ouest de Natal. On peut trouvé parmi les élèves y matriculés des trajectoires de vie interrompues par facteurs de risque comme criminalité, des adolescentes enceintes et drogues. Ces faits interférent directement avec les procès d intégration sociale et augmentent la violence, reproduisant les cycles de pauvreté et ainsi, limitant les possibilités d ascension sociale. Les résultats des procédées pédagogiques utilisées pendant les classes ont montré la nécessité d approfondir cet étude problématisant cette réalité et, incitant par les pratiques corporelles et discussion, la réflexion sur des thèmes comme facteurs de risque, temporalité, projets de vie et auto-connaissance. En profitant de l intérêt de ces jeunes pour la langage cinématographique comme une façon de mettre en ouvre ces réflexions et rapportant leur connaissance formel avec le savoir et expériences du groupe on a décidé de produire un film court de 15 minutes sur le quartier, idéalisé et produit collectivement. Pour ça, ont a réalisé 10 classes-ateliers avec les élèves qui ont été connus comme « le groupe du cinéma ». Les ateliers pédagogiques qui sont ici, au même temps, référence de recherche et procédée pédagogique, réaffirment la notion de résilience: la capacité de l individu de transformer un obstacle, une adversité ou même une tragédie personnel dans une situation positive ou comme un renfort de ce que nous avons de meilleur. Dans ce sens, cet étude peut aider les professeurs de toutes les matières, que travaillent a l école publique et que se trouvent dans ce contexte, considéré vulnérable, surtout le professeur d éducation physique. Ce travail peut aussi devenir une référence pour aborder des concepts et valeurs que nos aideront à renouveler cette vision de monde étroite et déterministe, responsable pour la reproduction des cycles de pauvreté et violence. Cet étude a été fondée sur des auteurs comme Edgar Morin, Bóris Cyrulnik et Conceição Almeida parmi d autres

A participação dos sujeitos e a reflexão coletiva das práticas na formação docente

Cet article propose, à partir d'une analyse de trois expériences différentes de la formation des enseignants, voir la pratique de l'enseignant comme une réalité et la comprendre, dans cette perspective, dynamique, génératrice de contenu et possible d être transformée. Une étude menée par un groupe de chercheurs de Sao Paulo do Potengi / RN avec des enseignants des écoles municipales dans les années 70, la mise en oeuvre du projet de réorientation curriculaire par le Bureau d Éducation de la ville de São Paulo - SP en 1989, et le cours Pédagogie de la Terre à l UFRN créée en 2002 sont pris en compte dans ce travail, comme des références dans la formation des enseignants qui démontrent à la fois les référentiel théorique et les actions développées sur la pertinence des réflexions par rapport à l'enseignement pratique comme point de départ quand on cherche à transformer l'école. Du matériel de lecture sur la manière dont ces processus de formation des événements a été possible de détecter la présence de deux éléments qui semblent être importants: la participation des personnes concernées et le reflet de leurs pratiques. Nous avons cherché à comprendre comment ces éléments apparaissent dans la pratique de deux étudiants du cours de Pédagogie de la Terre au cours de leurs classes de stage, en cherchant à identifier la façon dont ils font avancer ce point de vue de ce qui se passe dans le processus de formation. L'étude fait remarquer que la participation des sujets comme la réflexion collective des pratiques peuvent être cruciale pour la compréhension d'un enseignement qui peut être dynamique et de transformation des sujets, et qu elle peut se passer dans un processus de construction collective du savoir marquée par une refléxion et d une manière critique de faire et réflexive d'elle-même dans l'autonomie scolaire, améliorer la qualité de l'enseignement et le renforcement de l'enseignant et de l'élève comme des sujets actifs dans la reconstruction de leurs connaissances

Somos todos canibais: antropofagia, corpo e educação sensível

Cette étude présente l anthropophagie comme une notion théorique et experiementale du corps qui réhabilite le sensible et réveille le monde perçu. L argumentation fait ressortir la dimension sensible du corps et de la connaissance, en considerant sa sensibilité et motricité, corps qui ne se sépare pas de la nature et de l histoire, en actuant dans le monde comme présence vive, originaire, en mouvement ; en supposant un sujet qui, au même temps que construit ses propres senses, il dépend de l expérience de l autre et du monde, en créant et en recréant la culture, et il agrandit le processus de connaître, de sentir, de penser, d agir, d être, de se transformer. Cette attitude annonce une connaissance sensible et un corps qui est suscetible de sensations, mais d expréssions aussi, de communication, de création, aspects indispensables pour se pensar l éducation comme un space sensible, d apprantissage et réssignification de la culture ; que dévient possible la communion avec le corps, le temps, le space ; qu enseigne à réapprendre à voir le monde, que considère la réversibilité des senses et l esthésie comme champs de l expérience sensible et de l imputation des senses ; qu évoque la beauté des multiples léctures du vécu et qu agrandit la compréhension du soi et de l autre. L objectif de ce travail est comprendre l anthropophagie comme une attitude du corps et de la connaisance sensible, qu approfondit la rélation de l être au monde, la rélation avec l autre et permet la création de senses culturelles, ésthetiques et éxistentielles our l éducation. Nos présentons l attitude phénomologique de Maurice Merleau-Ponty comme référence théorique et méthodologique de notre recherche. Il s agit d une attitude de la pensée qui place la conaissance au centre de nos expériences vécues au monde ; une attitude qui ne propose pas un sens définitif des choses et des personnes et qui contribue pour la compréhension de l anthropophagie, du corps, du sensible, du monde et de l autre, en indiquant des développements de ces réflexions pour l éducation. En créant des horizonts de sense et strastégies de pérception sur l anthopophagie, nos considérons comme choix notre expérience vécu, comme les voyages; atelier d extension avec des élèves du cours de Technologie en Production Culturelle de l Institut Fédéral d Éducation, Science et Technologie du Rio Grande do Norte-IFRN, Campus Cidade Alta ; l anthropophagie comme élement de l Art Moderne Brésilien ; les créations et les récits des élèves ; images ; filmes et livres recherchés ; dialogues avec les penseurs Lévi-Strauss, Montaigne et Oswald de Andrade, qui constituent nos principales références conceptuelles et qui ont permis traversé des savoirs et promouvoir un dialogue entre divers champs de connaissance, comme l Anthropologie, la Philosophie, l Art et l Éducation. Ces stratégies constituent le resultat partiel et inachevé d un processus de connaisance de soi et de l autre, que permet de revivre des mémoires, faire ressortir des couleurs, des senses, des goûts, des découvertes sensibles et encourageantes sur la connaissance, sur l art, des découvertes sur soi même, sur l autre, sur le monde, sur la vie, indiquant que l éducation peut être un processus fort sensible, dans lequel le corps est une présence indispensable, aussi comme le toucher, le créer, les delires, les affections, les encontres et l invention

Uso de técnicas de otimização baseadas em derivadas como suporte do planejamento operacional de redes de distribuição de energia elétrica

The usual programs for load flow calculation were in general developped aiming the simulation of electric energy transmission, subtransmission and distribution systems. However, the mathematical methods and algorithms used by the formulations were based, in majority, just on the characteristics of the transmittion systems, which were the main concern focus of engineers and researchers. Though, the physical characteristics of these systems are quite different from the distribution ones. In the transmission systems, the voltage levels are high and the lines are generally very long. These aspects contribute the capacitive and inductive effects that appear in the system to have a considerable influence in the values of the interest quantities, reason why they should be taken into consideration. Still in the transmission systems, the loads have a macro nature, as for example, cities, neiborhoods, or big industries. These loads are, generally, practically balanced, what reduces the necessity of utilization of three-phase methodology for the load flow calculation. Distribution systems, on the other hand, present different characteristics: the voltage levels are small in comparison to the transmission ones. This almost annul the capacitive effects of the lines. The loads are, in this case, transformers, in whose secondaries are connected small consumers, in a sort of times, mono-phase ones, so that the probability of finding an unbalanced circuit is high. This way, the utilization of three-phase methodologies assumes an important dimension. Besides, equipments like voltage regulators, that use simultaneously the concepts of phase and line voltage in their functioning, need a three-phase methodology, in order to allow the simulation of their real behavior. For the exposed reasons, initially was developped, in the scope of this work, a method for three-phase load flow calculation in order to simulate the steady-state behaviour of distribution systems. Aiming to achieve this goal, the Power Summation Algorithm was used, as a base for developing the three phase method. This algorithm was already widely tested and approved by researchers and engineers in the simulation of radial electric energy distribution systems, mainly for single-phase representation. By our formulation, lines are modeled in three-phase circuits, considering the magnetic coupling between the phases; but the earth effect is considered through the Carson reduction. It s important to point out that, in spite of the loads being normally connected to the transformer s secondaries, was considered the hypothesis of existence of star or delta loads connected to the primary circuit. To perform the simulation of voltage regulators, a new model was utilized, allowing the simulation of various types of configurations, according to their real functioning. Finally, was considered the possibility of representation of switches with current measuring in various points of the feeder. The loads are adjusted during the iteractive process, in order to match the current in each switch, converging to the measured value specified by the input data. In a second stage of the work, sensibility parameters were derived taking as base the described load flow, with the objective of suporting further optimization processes. This parameters are found by calculating of the partial derivatives of a variable in respect to another, in general, voltages, losses and reactive powers. After describing the calculation of the sensibility parameters, the Gradient Method was presented, using these parameters to optimize an objective function, that will be defined for each type of study. The first one refers to the reduction of technical losses in a medium voltage feeder, through the installation of capacitor banks; the second one refers to the problem of correction of voltage profile, through the instalation of capacitor banks or voltage regulators. In case of the losses reduction will be considered, as objective function, the sum of the losses in all the parts of the system. To the correction of the voltage profile, the objective function will be the sum of the square voltage deviations in each node, in respect to the rated voltage. In the end of the work, results of application of the described methods in some feeders are presented, aiming to give insight about their performance and acuity

Conversor CC/CA de alta freqüência baseado em inversores ressonantes com comutação seqüencial para excitação de uma tocha indutiva a plasma térmico

This work describes the study, the analysis, the project methodology and the constructive details of a high frequency DC/AC resonant series converter using sequential commutation techniques for the excitation of an inductive coupled thermal plasma torch. The aim of this thesis is to show the new modulation technique potentialities and to present a technological option for the high-frequency electronic power converters development. The resonant converter operates at 50 kW output power under a 400 kHz frequency and it is constituted by inverter cells using ultra-fast IGBT devices. In order to minimize the turn-off losses, the inverter cells operates in a ZVS mode referred by a modified PLL loop that maintains this condition stable, despite the load variations. The sequential pulse gating command strategy used it allows to operate the IGBT devices on its maximum power limits using the derating and destressing current scheme, as well as it propitiates a frequency multiplication of the inverters set. The output converter is connected to a series resonant circuit constituted by the applicator ICTP torch, a compensation capacitor and an impedance matching RF transformer. At the final, are presented the experimental results and the many tests achieved in laboratory as form to validate the proposed new technique

Aplicação de sistemas multi-classificadores no diagnóstico de falhas em motores de indução trifásicos

Equipment maintenance is the major cost factor in industrial plants, it is very important the development of fault predict techniques. Three-phase induction motors are key electrical equipments used in industrial applications mainly because presents low cost and large robustness, however, it isn t protected from other fault types such as shorted winding and broken bars. Several acquisition ways, processing and signal analysis are applied to improve its diagnosis. More efficient techniques use current sensors and its signature analysis. In this dissertation, starting of these sensors, it is to make signal analysis through Park s vector that provides a good visualization capability. Faults data acquisition is an arduous task; in this way, it is developed a methodology for data base construction. Park s transformer is applied into stationary reference for machine modeling of the machine s differential equations solution. Faults detection needs a detailed analysis of variables and its influences that becomes the diagnosis more complex. The tasks of pattern recognition allow that systems are automatically generated, based in patterns and data concepts, in the majority cases undetectable for specialists, helping decision tasks. Classifiers algorithms with diverse learning paradigms: k-Neighborhood, Neural Networks, Decision Trees and Naïves Bayes are used to patterns recognition of machines faults. Multi-classifier systems are used to improve classification errors. It inspected the algorithms homogeneous: Bagging and Boosting and heterogeneous: Vote, Stacking and Stacking C. Results present the effectiveness of constructed model to faults modeling, such as the possibility of using multi-classifiers algorithm on faults classification

Análise teórica e experimental de superfícies seletivas de freqüência e suas aplicações em antenas planares

This work presents a theoretical and numerical analysis of structures using frequency selective surfaces applied on patch antennas. The FDTD method is used to determine the time domain reflected fields. Applications of frequency selective surfaces and patch antennas cover a wide area of telecommunications, especially mobile communications, filters and WB antennas. scattering parameters are obteained from Fourier Transformer of transmited and reflected fields in time domain. The PML are used as absorbing boundary condition, allowing the determination of the fields with a small interference of reflections from discretized limit space. Rectangular patches are considered on dielectric layer and fed by microstrip line. Frequency selective surfaces with periodic and quasi-periodic structures are analyzed on both sides of antenna. A literature review of the use of frequency selective surfaces in patch antennas are also performed. Numerical results are also compared with measured results for return loss of analyzed structures. It is also presented suggestions of continuity to this work

Desenvolvimento de uma ferramenta computacional para aplicação em métodos de elevação por bombeio centrífugo submerso

The Electrical Submersible Pump (ESP) has been one of the most appropriate solutions for lifting method in onshore and offshore applications. The typical features for this application are adverse temperature, viscosity fluids and gas environments. The difficulties in equipments maintenance and setup contributing to increasing costs of oil production in deep water, therefore, the optimization through automation can be a excellent approach for decrease costs and failures in subsurface equipment. This work describe a computer simulation related with the artificial lifting method ESP. This tool support the dynamic behavior of ESP approach, considering the source and electric energy transmission model for the motor, the electric motor model (including the thermal calculation), flow tubbing simulation, centrifugal pump behavior simulation with liquid nature effects and reservoir requirements. In addition, there are tri-dimensional animation for each ESP subsytem (transformer, motor, pump, seal, gas separator, command unit). This computer simulation propose a improvement for monitoring oil wells for maximization of well production. Currenty, the proprietaries simulators are based on specific equipments manufactures. Therefore, it is not possible simulation equipments of another manufactures. In the propose approach there are support for diverse kinds of manufactures equipments