On the Relation between Mains-Side Current THD and DC Link Voltage Loop Gain in Grid-Connected Unity Power Factor Operating Converters

<p>It is well-known that attainable DC link voltage loop bandwidth in grid-connected converters operating with unity power factor is limited due to trade-off with AC-side current total harmonic distortion (THD). The letter reveals that THD requirement directly imposes the value of voltage loop gain magnitude at double-grid frequency; therefore the dynamic performance may be improved without deteriorating the grid-side current quality by modifying the controller structure such that the loop gain magnitude at double-grid frequency and the crossover frequency are decoupled. Experimental results validate the revealed findings.</p>

On the Relation between Mains-Side Current THD and DC Link Voltage Loop Gain in Grid-Connected Unity Power Factor Operating Converters

<p>It is well-known that attainable DC link voltage loop bandwidth in grid-connected converters operating with unity power factor is limited due to trade-off with AC-side current total harmonic distortion (THD). The letter reveals that THD requirement directly imposes the value of voltage loop gain magnitude at double-grid frequency; therefore the dynamic performance may be improved without deteriorating the grid-side current quality by modifying the controller structure such that the loop gain magnitude at double-grid frequency and the crossover frequency are decoupled. Experimental results validate the revealed findings.</p>

Capela da Fazenda Veneza: análise comparativa da precisão de nuvens de pontos obtidas por diferentes ferramentas e técnicas de fotogrametria

A Capela da Fazenda Veneza, projetada pelo arquiteto Decio Tozzi, é uma edificação de grande importância tanto pela sua plasticidade e representatividade, quanto para o patrimônio da arquitetura moderna brasileira. A edificação, localizada na cidade de Valinhos, SP, já conquistou diversas premiações nacional e internacionalmente. Considerando a importância da obra, viu-se a necessidade de realizar um levantamento geométrico por meio da Fotogrametria digital. Tendo em vista o leque disponível de software para processamento fotogramétrico, esta pesquisa tem como objetivo comparar a precisão das dimensões das nuvens de pontos densas, em relação às dimensões reais da edificação, geradas nos programas mais utilizados em pesquisas científicas. Esta pesquisa foi desenvolvida a partir das seguintes etapas: (i) Revisão Sistemática da Literatura (RSL); (ii) Medição in loco da edificação; (iii) Planejamento de voo: livre com utilização de alvos (V1); e autônomo com double grid e utilização de pontos de controle estabelecidos por meio de estação total (V2); (iv) coleta de dados por Fotogrametria aérea com sistema de aeronave remotamente pilotada (V1 e V2); (v) Processamento dos dados obtidos nos programas mais utilizados (V1 e V2); (vi) Comparação das dimensões reais com as medidas obtidas nas nuvens densas; e (vii) Análise estatística. Observou-se que a precisão da nuvem de pontos é influenciada pelas técnicas e equipamentos utilizados na coleta de dados e pelo software empregado no processamento. Esta investigação contribui para realização de futuros levantamentos Fotogramétricos, uma vez que aponta as melhores práticas para alcançar maior precisão.

Enhanced Control Scheme for a Three-Phase Grid-Connected PV Inverter under Unbalanced Fault Conditions

This paper presents an improved control strategy to cancel the double grid frequency oscillations in the active power, reactive power, and DC-link voltage of a three-phase grid-connected photovoltaic (PV) system under unbalanced grid condition. To achieve these goals, an enhanced positive–negative-sequence control (PNSC) to remove oscillations of active power and an instantaneous active–reactive control (IARC) to mitigate the fluctuations of active and reactive power, simultaneously, are suggested. These methods are also effective to reduce the oscillations of the DC-link voltage. To track the desired unbalanced or harmonic reference currents, improved proportional resonant (PR) current controllers have been designed using the Bode frequency analysis. Simulation studies are carried out via Matlab/Simulink® software to verify the effectiveness of the suggested control strategies.

Simulation Models For Three-Phase Grid Connected PV Inverters Enabling Current Limitation Under Unbalanced Faults

Normally unbalanced grid voltage dips may lead to unbalanced non-sinusoidal current injections, DC-link voltage oscillations, and active and/or reactive power oscillations with twice the grid fundamental frequency in three-phase grid-connected Photovoltaic (PV) systems. Double grid frequency oscillations at the DC-link of the conventional two-stage PV inverters can further deteriorate the DC-link capacitor, which is one of the most important limiting components in the system. Proper control of these converters may efficiently address this problem. In such solutions, Current Reference Calculation (CRC) is one of the most important issues that should be coped with the reliable operation of grid-connected converters under unbalanced grid faults. Therefore, this paper proposes and simulates CRC methods and presents the results in order to improve the quality of the grid-connected PV system under unbalanced grid voltage fault.

Optical Spectra of Bi2Se3: The Effects of Electron-Hole Interactions

Bi2Se3 has recently become the focus of research development due to its unique transport properties. It is a narrow band gap semiconductor with conducting states on its surface. A reliable and accurate calculation of the optical spectra including excitonic effects is very limited for this material. One of the reasons is that such calculations are computationally demanding since they require a very dense k-point sampling of the Brillouin zone. In this work, we use density functional theory as implemented in Quantum Espresso package to calculate the ground state properties of this material. Optical spectra are calculated within many-body perturbation theory by solving the Bethe-Salpeter equation in Yambo code to account for electron-hole interaction. A double-grid method implemented in Yambo helps us to do accurate calculations of the optical spectra with inexpensive computational cost. Furthermore, we expect that in bulk semiconductor with a narrow gap, electron-electron interaction is weak due to environmental screening. For this reason, to reduce the computational efforts, in this work we neglect the electron-electron interaction.