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.

Analysis of antidiarrhoeic effect of plants used in popular medicine

People customarily use the extracts of plants known to have antidiarrhoeal effects without any scientific base to explain the action of the extract. For this reason, an investigation was undertaken with a view to determining the efficacy of the effects of the brute aqueous extract (BAE) of the leaves of Psidium guajava (guava), Stachytarpheta cayenensis (bastard vervain), Polygonum punctatum (water. smartweed), Eugenia uniflora (Brazil or Surinam cherry) and Aster squamatus (zé-da-silva) on the intestinal transport of water in rats and on the gastrointestinal propulsion in mice. With the exception of the BAE of S. cayenensis, all other BAE's have increased the absorption of water in one or more intestinal portion in relation to the control group. All tested BAE, except that of P. punctatum, reduced the gastrointestinal propulsion in relation to that of the control group. The results indicate that the BAE of the leaves of P. guajava, S. cayenensis, P. punctatum, E. uniflora and A. squamatus have a potential antidiarrhoeic effect to be confirmed by additional investigations in animals infected with enteropathogenic agents.

Educación popular y nutrición infantil: experiencia de trabajo con mujeres en una zona rural de México

OBJETIVO: Se realizó una intervención comunitaria bajo la estrategia de promoción de la salud, con el objetivo de desarrollar un programa de educación para la salud con mujeres. MÉTODOS: Se analizó la metodología de educación popular; con la finalidad de generar procesos organizativos y de participación social que mejoren la nutrición y sobrevivencia infantil. RESULTADOS: Los principales resultados, se relacionan con la generación de procesos autogestivos, la conformación de un grupo de promotoras de salud que han impulsado la organización de las mujeres enfocando su trabajo a mejorar la nutrición infantil y la salud familiar. Las promotoras han tomado en sus manos el programa de vigilancia epidemiológica en nutrición infantil y en conjunto con las mujeres han emprendido una serie de acciones para mejorar la nutrición de los niños y los porcentajes de desnutrición en los niños que participan en el programa de nutrición infantil han iniciado un descenso (64% a 62%). CONCLUSIONES: Los programas de nutrición infantil tienen mayores posibilidades de éxito en la medida que logran involucrar a la población en la resolución de esta problemática, eso es posible cuando se utiliza una metodología que propicie la participación de los individuos y se generen espacios que les permitan realizar una práctica transformadora de su realidad. La metodología de la educación popular proporciona las pautas en ese sentido. Es necesario continuar ampliando las experiencias educativas en educación para la salud con este tipo de metodología.

Avaliação do conhecimento popular e práticas cotidianas em saúde bucal

OBJETIVO: Avaliar o conhecimento popular e as práticas cotidianas em saúde bucal de usuários de serviços públicos de saúde. MÉTODOS: A população estudada foi selecionada a partir de uma amostra estratificada de usuários que procuraram atendimento nas unidades sanitárias da zona urbana de Santa Maria, RS. Os dados foram coletados por meio de entrevista semi-estruturada e organizados em conjuntos de categorias descritivas, permitindo sua distribuição em tabela de freqüência. RESULTADOS: Verificou-se que predominam usuários entre 21 e 40 anos de idade, do sexo feminino e com padrão socioeconômico baixo. A busca pela saúde e o controle das doenças bucais são atribuídos à responsabilidade individual de realizar a higiene bucal e procurar tratamento dentário. A presença e os benefícios do flúor no creme dental e na água de beber não foram reconhecidos pela população estudada. CONCLUSÕES: Os programas de saúde devem considerar os aspectos relativos ao conhecimento e as práticas em saúde bucal, para viabilizar o processo de capacitação da população e promover a responsabilização coletiva da promoção da saúde em todos os níveis da sociedade.

Thinking over b‐learning strategy: the MIPO model approach

This article describes the main research results in a new methodology, in which the stages and strategies of the technology integration process are identified and described. A set of principles and recommendations are therefore presented. The MIPO model described in this paper is a result of the effort made regarding the understanding of the main success features of good practices, in the web environment, integrated in the information systems/information technology context. The initial model has been created, based on experiences and literature review. After that, it was tested in the information and technology system units at higher school and also adapted as a result of four cycles of an actionresearch work combined with a case study research. The information, concepts and procedures presented here give support to teachers and instructors, instructional designers and planning teams – anyone who wants to develop effective b‐learning instructions.

A Cultura popular portuguesa e o discurso do poder

A Cultura Popular Portuguesa e o Discurso do Poder: Práticas e Representações do Moliceiro" estuda um objecto e o discurso por ele evocado, enquanto representação, invenção e reinvenção da cultura popular de uma região portuguesa. Contudo, esta comunicação pretende também ver através do objecto, isto é, "atravessar a [sua] opacidade inoportuna", tal como propõe Michel Foucault em A Arqueologia do Saber. Esse objecto é o barco moliceiro da Ria de Aveiro que, mais do que um caso de tradição versus modernidade, constitui uma representação da identidade cultural de uma comunidade intimamente ligada ao ecossistema lagunar. Os painéis do barco moliceiro são assim representações simbólicas intersemióticas dos valores, práticas e representações partilhadas pela comunidade local. Os textos icónicos e escritos patentes em cada barco são produto de uma rede de circunstâncias políticas, ideológicas, sociais e económicas, dificilmente reconhecidas mesmo por aqueles que desenham, pintam e escrevem (e vivem) sob a sua influência. Ao longo do século XX, o moliceiro e seus painéis participaram numa complexa dialéctica entre as representações do discurso oficial e a sua real função social, económica e simbólica, gerando todo um imaginário histórico, todo um "inventário" (cf. Gramsci) que motivou, contextualizou e sustentou esta forma única de arte popular.

Popular beliefs regarding the treatment of senile cataract

OBJECTIVE: To identify popular beliefs regarding the treatment of senile cataract in patients enrolled in the community health programs on eye rehabilitation. METHODS: A cross-sectional survey was carried out using an interview questionnaire that was applied to 776 subjects drawn from a non-probabilistic sample in five cities of the state of São Paulo. The sample was made up of 47.2% males and 52.8% females, aged 50 to 96 years (average age 71.6 years). RESULTS: Of the total of subjects studied, 41.9% had never attended school, and 78.5% were no longer in the employment market. Most (85.1%) credited the sight restoration to cataract surgery. Among those unconvinced, 47.4% asserted that sight restoration depended only on God's will. A greater proportion of women than men (p 0.0000) believed in the association of cataract and menopause, maternity, and menstrual periods and they admitted using herbal and rose teas for treating cataract. CONCLUSIONS: Misbeliefs related to the causes and treatment of senile cataract were identified, most probably of sociocultural basis, indicating the need of education on the subject.

A new control strategy with saturation effect compensation for an autonomous induction generator drivenby wide speed range turbines

This paper presents a variable speed autonomous squirrel cage generator excited by a current-controlled voltage source inverter to be used in stand-alone micro-hydro power plants. The paper proposes a system control strategy aiming to properly excite the machine as well as to achieve the load voltage control. A feed-forward control sets the appropriate generator flux by taking into account the actual speed and the desired load voltage. A load voltage control loop is used to adjust the generated active power in order to sustain the load voltage at a reference value. The control system is based on a rotor flux oriented vector control technique which takes into account the machine saturation effect. The proposed control strategy and the adopted system models were validated both by numerical simulation and by experimental results obtained from a laboratory prototype. Results covering the prototype start-up, as well as its steady-state and dynamical behavior are presented. (C) 2011 Elsevier Ltd. All rights reserved.

A strategy to extend reactive distillation column performance under catalyst deactivation

This work addresses the effects of catalyst deactivation and investigates methods to reduce their impact on the reactive distillation columns performance. The use of variable feed quality and reboil ratio are investigated using a rigorous dynamic model developed in gPROMS and applied to an illustrative example, i.e., the olefin metathesis system, wherein 2-pentene reacts to form 2-butene and 3-hexene. Three designs and different strategies on column energy supply to tackle catalyst deactivation are investigated and the results compared.

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.

HVDC transmission systems: Bipolar back-to-back diode clamped multilevel converter with fastoptimum-predictive control and capacitor balancing strategy

Voltage source multilevel power converter structures are being considered for high power high voltage applications where they have well known advantages. Recently, full back-to-back connected multilevel neutral diode clamped converters (NPC) have been used in high voltage direct current (HVDC) transmission systems. Bipolar back-to-back connection of NPCs have advantages in long distance HVDC transmission systems, but highly increased difficulties to balance the dc capacitor voltage dividers on both sending and receiving end NPCs. This paper proposes a fast optimum-predictive controller to balance the dc capacitor voltages and to control the power flow in a long distance HVDCsystem using bipolar back-to-back connected NPCs. For both converter sides, the control strategy considers active and reactive power to establish ac grid currents on sending and receiving ends, while guaranteeing the balancing of both NPC dc bus capacitor voltages. Furthermore, the fast predictivecontroller minimizes the semiconductor switching frequency to reduce global switching losses. The performance and robustness of the new fast predictive control strategy and the associated dc capacitors voltage balancing are evaluated. (C) 2011 Elsevier B.V. All rights reserved.

Multiagent system for adaptive strategy formulation in electricity markets

Electricity markets are complex environments with very particular characteristics. MASCEM is a market simulator developed to allow deep studies of the interactions between the players that take part in the electricity market negotiations. This paper presents a new proposal for the definition of MASCEM players’ strategies to negotiate in the market. The proposed methodology is multiagent based, using reinforcement learning algorithms to provide players with the capabilities to perceive the changes in the environment, while adapting their bids formulation according to their needs, using a set of different techniques that are at their disposal.

Contexts-management strategy in considering the security in urban computing based on urban design

Urban Computing (UrC) provides users with the situation-proper information by considering context of users, devices, and social and physical environment in urban life. With social network services, UrC makes it possible for people with common interests to organize a virtual-society through exchange of context information among them. In these cases, people and personal devices are vulnerable to fake and misleading context information which is transferred from unauthorized and unauthenticated servers by attackers. So called smart devices which run automatically on some context events are more vulnerable if they are not prepared for attacks. In this paper, we illustrate some UrC service scenarios, and show important context information, possible threats, protection method, and secure context management for people.

Cost dependent strategy for electricity markets bidding based on adaptive reinforcement learning

Electricity markets are complex environments, involving a large number of different entities, playing in a dynamic scene to obtain the best advantages and profits. MASCEM is a multi-agent electricity market simulator to model market players and simulate their operation in the market. Market players are entities with specific characteristics and objectives, making their decisions and interacting with other players. MASCEM provides several dynamic strategies for agents’ behavior. This paper presents a method that aims to provide market players with strategic bidding capabilities, allowing them to obtain the higher possible gains out of the market. This method uses a reinforcement learning algorithm to learn from experience how to choose the best from a set of possible bids. These bids are defined accordingly to the cost function that each producer presents.