1,200 research outputs found
Retificador buck trifásico unidirecional PWM isolado em alta-frequência por único estágio
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2009Descreve-se uma nova topologia de conversor CA-CC trifásico isolado em alta-frequência por único estágio de potência. O novo conversor é constituído de um retificador Buck unidirecional trifásico associado a um transformador forward/flyback com desmagnetização na carga. Para a exploração da nova topologia foram realizados estudos sobre retificadores Buck, algumas técnicas populares de modulação SPWM escalar, uma técnica clássica de filtragem das harmônicas das correntes de entrada e uma técnica de modelagem por espaço-de-estados e controle contínuo do retificador Buck em sistema de coordenadas dq obtidas por transformação de Clarke/Park. Para a obtenção da isolação em alta-frequência sem conversores adicionais foram estudados os princípios de operação do conversor forward/flyback em modo de condução descontínuo para posterior integração do transformador ao retificador trifásico. Os conhecimentos obtidos foram concentrados no retificador Buck trifásico isolado em altafrequência onde foram exploradas a modulação da ponte retificadora, os estados de operação associados ao transformador e a desmagnetização na carga. Ainda, foram obtidos os modelos em espaço-de-estados em coordenadas dq para o retificador Buck com transformador e projetados compensadores PI contínuos para o controle pela tensão na carga. Para a comprovação do conceito da topologia proposta foi projetado e implementado um protótipo de 2;5 kW para conexão em rede trifásica sem neutro de 220 V e tensão de 48 V para a carga regulada por circuito controlador digital baseado na arquitetura de baixo custo dsPIC.This work presents a new topology for an AC-DC three-phase converter with single-stage high-frequency isolation. The new converter is composed of an unidirectional three-phase Buck rectifier and a forward/flyback transformer with demagnetization through the load. The study of Buck rectifiers principles has been performed as a basis to develop the new topology. The scalar SPWM modulation techniques, the classic design of filters to input currents and a state-space modeling technique at dq components to design the feedback control for a Buck rectifier have been studied. The forward/flyback converter operating at discontinuous conduction mode has been studied to allow a high-frequency isolation to the Buck rectifier without the cascade of extra switched converters. The three-phase Buck rectifier with high-frequency isolation has been analyzed regarding pulse width modulation, operational states and requirements for demagnetization through the load. Moreover, the state-space models at dq components have been derived and standard PI regulators have been designed to control the proposed rectifier. The validation of the proposed topology has been performed on an experimental prototype with the following specification 220 V three-wires mains source and 2:5 kW at 48 V output regulated by a digital control based on dsPIC low cost architecture
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[News Clip: Pearl Buck]
No full textVideo footage from the WBAP-TV station in Fort Worth, Texas to accompany a news story about an author, who came to Dallas to claim her prizes. Novelist Pearl Buck arrived for the 6th annual Club Woman's Forum
Truck buck rake
No full textTitle from PDF cover (viewed on November 7, 2017).This archived document is maintained by the State Library of Oregon as part of the Oregon Documents Depository Program. It is for informational purposes and may not be suitable for legal purposes.Mode of access: Internet from the Oregon Government Publications Collection.Text in English
Pearl Buck Revisited
No full textIn 2002, the author published a column on Pearl Buck. Ten years later, the author revisits the topic of Nobel Laureate Pearl Sydenstricker Buck, whose life continues to generate new literature
Author Pearl Buck given Key to City by Councilman Freeman Woods
No full textVice Mayor G. Freeman Woods proclaimed author Pearl Buck an honorary citizen of Tucson in March of 1965. She was campaigning for funds for her Pearl S. Buck Foundation, which aided Korean-American children. [Chapter 9 Page 185
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[Photograph of author Pearl S. Buck, 4]
No full textPhotograph of Pearl Sydenstricker Buck, also known by her Chinese name Sai Zhenzhu. Buck is seated on the sofa in the Love Field conference room with an unknown man and having her portrait taken. Buck is notable for being a writer and novelist
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[Photograph of author Pearl S. Buck, 3]
No full textPhotograph of Pearl Sydenstricker Buck, also known by her Chinese name Sai Zhenzhu. Buck is seated on the sofa in the Love Field conference room with an unknown man and having her portrait taken. Buck is notable for being a writer and novelist
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[Photograph of author Pearl S. Buck]
No full textPhotograph of Pearl Sydenstricker Buck, also known by her Chinese name Sai Zhenzhu. Buck is seated on the sofa in the Love Field conference room with an unknown man and having her portrait taken. Buck is notable for being a writer and novelist
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[Photograph of author Pearl S. Buck, 2]
No full textPhotograph of Pearl Sydenstricker Buck, also known by her Chinese name Sai Zhenzhu. Buck is seated on the sofa in the Love Field conference room with an unknown man and having her portrait taken. Buck is notable for being a writer and novelist
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