Direct Power Control of Matrix Converter Based Unified Power Flow Controllers

This paper presents the Direct Power Control of Three-Phase Matrix Converters (DPC-MC) operating as Unified Power Flow Controllers (UPFC). Since matrix converters allow direct AC/AC power conversion without intermediate energy storage link, the resulting UPFC has reduced volume and cost, together with higher reliability. Theoretical principles of DPC-MC method are established based on an UPFC model, together with a new direct power control approach based on sliding mode control techniques. As a result, active and reactive power can be directly controlled by selection of an appropriate switching state of matrix converter. This new direct power control approach associated to matrix converters technology guarantees decoupled active and reactive power control, zero error tracking, fast response times and timely control actions. Simulation results show good performance of the proposed system.

Power Electronics Didactic Modules for Direct Current Machine Control

Several didactic modules for an electric machinery laboratory are presented. The modules are dedicated for DC machinery control and get their characteristic curves. The didactic modules have a front panel with power and signal connectors and can be configurable for any DC motor type. The three-phase bridge inverter proposed is one of the most popular topologies and is commercially available in power package modules. The control techniques and power drives were designed to satisfy static and dynamic performance of DC machines. Each power section is internally self-protected against misconnections and short-circuits. Isolated output signals of current and voltage measurements are also provided, adding versatility for use either in didactic or research applications. The implementation of such modules allowed experimental confirmation of the expected performance.

A Flexible Architecture for the Computation of Direct and Inverse Transforms in H.264/AVC Video Codecs

A new high throughput and scalable architecture for unified transform coding in H.264/AVC is proposed in this paper. Such flexible structure is capable of computing all the 4x4 and 2x2 transforms for Ultra High Definition Video (UHDV) applications (4320x7680@ 30fps) in real-time and with low hardware cost. These significantly high performance levels were proven with the implementation of several different configurations of the proposed structure using both FPGA and ASIC 90 nm technologies. In addition, such experimental evaluation also demonstrated the high area efficiency of theproposed architecture, which in terms of Data Throughput per Unit of Area (DTUA) is at least 1.5 times more efficient than its more prominent related designs(1).

Direct multisearch for multiobjective optimization

In practical applications of optimization it is common to have several conflicting objective functions to optimize. Frequently, these functions are subject to noise or can be of black-box type, preventing the use of derivative-based techniques. We propose a novel multiobjective derivative-free methodology, calling it direct multisearch (DMS), which does not aggregate any of the objective functions. Our framework is inspired by the search/poll paradigm of direct-search methods of directional type and uses the concept of Pareto dominance to maintain a list of nondominated points (from which the new iterates or poll centers are chosen). The aim of our method is to generate as many points in the Pareto front as possible from the polling procedure itself, while keeping the whole framework general enough to accommodate other disseminating strategies, in particular, when using the (here also) optional search step. DMS generalizes to multiobjective optimization (MOO) all direct-search methods of directional type. We prove under the common assumptions used in direct search for single objective optimization that at least one limit point of the sequence of iterates generated by DMS lies in (a stationary form of) the Pareto front. However, extensive computational experience has shown that our methodology has an impressive capability of generating the whole Pareto front, even without using a search step. Two by-products of this paper are (i) the development of a collection of test problems for MOO and (ii) the extension of performance and data profiles to MOO, allowing a comparison of several solvers on a large set of test problems, in terms of their efficiency and robustness to determine Pareto fronts.

Fast optimum-predictive control and capacitor voltage balancing strategy for bipolar back-to-back NPC converters in high-voltage direct current transmission systems

Multilevel power converters have been introduced as the solution for high-power high-voltage switching applications where they have well-known advantages. Recently, full back-to-back connected multilevel neutral point diode clamped converters (NPC converter) have been used inhigh-voltage direct current (HVDC) transmission systems. Bipolar-connected back-to-back NPC converters have advantages in long-distance HVDCtransmission systems over the full back-to-back connection, but greater difficulty to balance the dc capacitor voltage divider on both sending and receiving end NPC converters. This study shows that power flow control and dc capacitor voltage balancing are feasible using fast optimum-predictive-based controllers in HVDC systems using bipolar back-to-back-connected five-level NPC multilevel converters. For both converter sides, the control strategytakes in account active and reactive power, which establishes ac grid currents in both ends, and guarantees the balancing of dc bus capacitor voltages inboth NPC converters. Additionally, the semiconductor switching frequency is minimised to reduce switching losses. The performance and robustness of the new fast predictive control strategy, and its capability to solve the DC capacitor voltage balancing problem of bipolar-connected back-to-back NPCconverters are evaluated.

Matrix Converter-Based Unified Power-Flow Controllers: Advanced Direct Power Control Method

This paper presents a direct power control (DPC) for three-phase matrix converters operating as unified power flow controllers (UPFCs). Matrix converters (MCs) allow the direct ac/ac power conversion without dc energy storage links; therefore, the MC-based UPFC (MC-UPFC) has reduced volume and cost, reduced capacitor power losses, together with higher reliability. Theoretical principles of direct power control (DPC) based on sliding mode control techniques are established for an MC-UPFC dynamic model including the input filter. As a result, line active and reactive power, together with ac supply reactive power, can be directly controlled by selecting an appropriate matrix converter switching state guaranteeing good steady-state and dynamic responses. Experimental results of DPC controllers for MC-UPFC show decoupled active and reactive power control, zero steady-state tracking error, and fast response times. Compared to an MC-UPFC using active and reactive power linear controllers based on a modified Venturini high-frequency PWM modulator, the experimental results of the advanced DPC-MC guarantee faster responses without overshoot and no steady-state error, presenting no cross-coupling in dynamic and steady-state responses.

Paroles de femmes : positionnement et stratégies de résistance

Nées des travaux des féministes américaines, les gender studies, faut-il le rappeler, se sont constituées aux Etats Unis dans les années quatre-vingts à partir des questionnements sur les rapports hommes / femmes au sein de la société. Depuis les années soixante-dix, la French Theory avait déjà joué un rôle très important dans le débat théorique américain avec les philosophes Gilles Deleuze, Jacques Derrida, Michel Foucault, Jean-François Lyotard… Remettant sans cesse en question le pouvoir, l’institution et la manière de penser, ils se sont distingués par la force de leur posture critique et par leur engagement. Aussi faut-il rappeler l’importance des travaux et des réflexions de femmes intellectuelles françaises, comme Hélène Cixous, Julia Kristeva, Luce Irigaray et tant d’autres pour les études du genre.

Écrire à l' université: jeux et enjeux didactiques

Nous présentons, dans cette communication, les resultats d'une étude menée dans le cours d'expression orale et écrite dispensé en premier année à l'Escola Superior de Educação de Lisbonne.

Pour une approche contrastive du présent simple en français et en portugais

Les temps du passé ont toujours constitué une pierre d’achoppement aussi bien dans l’enseignement du français aux étudiants lusophones que dans celui du portugais aux francophones. Le flot continu d’articles sur ce sujet attesterait, à lui seul, la difficulté du problème. Mais aussi étonnant que cela puisse paraître, il n’existe à ce jour aucune étude systématique qui aborde sur une base théorique le présent simple dans le passage du français vers le portugais et/ou vice-versa. Or, une telle étude nous paraît une voie de recherche intéressante et fructueuse qui ouvre de nombreuses perspectives de recherche, dont les possibilités d’application, que ce soit au domaine de l’enseignement des langues étrangères ou celui de la traduction, ne sont pas négligeables. Cette réflexion est d’autant plus urgente que l’emploi du présent simple pose de sérieux problèmes aux élèves lusophones plus inexpérimentés. En effet, ces derniers ont parfois beaucoup de peine à trouver les bonnes correspondances du présent simple en portugais. Afin d’aboutir à des conclusions fiables sur les similarités et les divergences entre le français et le portugais quant aux conditions d’apparition et au mode de fonctionnement du présent simple, nous nous attacherons, dans l’étude contrastive qui suit, à examiner des échantillons de textes littéraires français traduits en portugais et des extraits de textes littéraires portugais traduits en français1. Il s’agira essentiellement de montrer, en recourant à la Théorie des Opérations Énonciatives d’Antoine Culioli (Culioli, 1990; Campos & Xavier, 1991; Campos, 1997, 1998, entre autres), par quels moyens linguistiques le portugais exprime les valeurs aspectuo-temporelles associées au présent simple en français.

Cost of schizophrenia: direct costs and use of resources in the State of São Paulo

OBJECTIVE: To estimate the direct costs of schizophrenia for the public sector. METHODS: A study was carried out in the state of São Paulo, Brazil, during 1998. Data from the medical literature and governmental research bodies were gathered for estimating the total number of schizophrenia patients covered by the Brazilian Unified Health System. A decision tree was built based on an estimated distribution of patients under different types of psychiatric care. Medical charts from public hospitals and outpatient services were used to estimate the resources used over a one-year period. Direct costs were calculated by attributing monetary values for each resource used. RESULTS: Of all patients, 81.5% were covered by the public sector and distributed as follows: 6.0% in psychiatric hospital admissions, 23.0% in outpatient care, and 71.0% without regular treatment. The total direct cost of schizophrenia was US$191,781,327 (2.2% of the total health care expenditure in the state). Of this total, 11.0% was spent on outpatient care and 79.2% went for inpatient care. CONCLUSIONS: Most schizophrenia patients in the state of São Paulo receive no regular treatment. The study findings point out to the importance of investing in research aimed at improving the resource allocation for the treatment of mental disorders in Brazil.

Comportamentos interactivos das educadoras de infância em salas de creche em função do tipo de actividades e das características estruturais do contexto

O presente artigo pretende examinar a quantidade, qualidade e adequação dos comportamentos interactivos das educadoras em salas de creche, em actividades livres e estruturadas, investigando a sua relação com aspectos de estrutura destes contextos. Participaram neste estudo 30 responsáveis por salas de creche da Área Metropolitana do Porto (incluindo 5 auxiliares de acção educativa). Os comportamentos interactivos das educadoras foram avaliados com a Escala de Interacção Educador-Criança (Farran, & Collins 1995). Os resultados obtidos sugerem que as educadoras exibem maior quantidade de comportamentos interactivos no decurso de actividades estruturadas (r = .65) e que a adequação destes comportamentos é superior quando estes profissionais têm bacharelato ou licenciatura (rь=.57), quando auferem salários superiores (r = .42) e quando despendem menos horas de trabalho directo com as crianças (r = -.37). A qualidade dos comportamentos interactivos está relacionada com o salário auferido (r = .43). As implicações práticas dos resultados obtidos são discutidas com o objectivo de analisar formas possíveis de alcançar níveis de excelência em contextos de educação de infância.

Pratiques d’enseignement en lecture-écriture et apprentissages des élèves au début du primaire

Esta investigação pretende contribuir para o desenvolvimento da investigação interessada nas questões relativas ao ensino/ aprendizagem do modo escrito nos primeiros anos do primeiro ciclo do ensino básico, particularmente tendo em conta as práticas mais propensas a apoiar a aprendizagem bem-sucedida da leitura e de escrita. Especificamente, esta investigação tem como objetivo descrever as práticas de ensino observadas nas áreas da leitura e da escrita com 22 professores, mas também para relacionar essas práticas observadas com o desempenho em leitura e escrita dos seus alunos do primeiro e do segundo ano. Globalmente, os resultados indicam que as práticas observadas, tanto do ponto de vista dos Dispositivos mobilizados como do conteúdo ensinado, são variadas e contribuem para uma visão complexa da entrada na escrita. As análises de correlação sugerem que determinadas práticas, que geralmente procuram a participação activa das crianças e as interações com os outros, estão relacionados com o progresso dos alunos durante o ano letivo.

As imagens dos manuais escolares: representações mentais de professores e alunos relativamente à presença de imagens nos manuais escolares e à sua eficácia pedagógica

Sendo o manual escolar o recurso pedagógico mais utilizado por alunos e professores foi realizada uma investigação tendo por objectivo avaliar qualitativamente a forma comunicacional de um conjunto de manuais escolares do 2º ciclo do ensino básico1. A importância atribuída atualmente à imagem é patente nos manuais escolares, sob pretexto de se tornarem mais apelativos e mais eficazes. Tal como em outras áreas em que a quantidade de imagens acaba por se transformar em poluição visual porque o ser humano não tem capacidade para reagir, simultaneamente, a um demasiado número de estímulos, nas estratégias comunicacionais dos manuais escolares este problema deve ser acautelado porque delas depende a sua qualidade pedagógica. As investigações não comprovam que exista uma relação direta entre a presença de ilustrações num texto e o aumento da sua compreensão. Pelo contrário, há estudos que sugerem que muitas ilustrações falham como potenciadoras da aprendizagem. Neste sentido, da investigação referida, consta uma análise ao rácio imagem/texto e uma auscultação a dois grupos de amostra - professores e alunos – sobre alguns aspectos gerais relativos à presença e eficácia pedagógica das ilustrações dos manuais escolares. Destacamos que, no caso dos alunos, apesar do seu nível de literacia ter constituído um obstáculo ao tratamento das questões, optámos por apresentar as suas respostas.

Qualidade do processamento sensorial e vinculação infantil

Estudou-se a relação entre a segurança da vinculação e a qualidade do processamento sensorial na primeira infância. Para o efeito, seleccionou-se uma amostra normativa de 40 díades mãe-bebé, com crianças entre os 11 e os 18 meses. Avaliou-se a qualidade da vinculação, observando a díade no procedimento Situação Estranha. Classificaram-se 17 (42,5%) das crianças no grupo de vinculação segura, sendo que as restantes 23 (57,5%) revelaram uma vinculação não segura. A qualidade do processamento sensorial avaliou-se através do Teste de Funções Sensoriais. Constatou-se que a segurança da vinculação infantil associava-se a um score agregando quatro factores ambientais (nível sócio-económico dos pais; existência de internamentos hospitalares; coeficiente de número de irmãos; local onde a criança passa o dia). O Teste de Funções Sensoriais não apresentou valor prognóstico relativamente ao tipo de vinculação. Porém, a boa qualidade no processamento da informação sensorial parece constituir um factor de resiliência no desenvolvimento da vinculação.

Comment on R. Woodroffe et al. Perspective in Ecology "To Fence or Not to Fence" (4 April 2014, Science, 344: 46-48)

Fences must be used with care in biodiversity conservation to avoid unintended consequences.