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Wu H.,Jiangsu Key Laboratory of New Energy Generation and Power Conversion | Wan C.,Beijing Spacecrafts | Sun K.,Tsinghua University | Xing Y.,Jiangsu Key Laboratory of New Energy Generation and Power Conversion
IEEE Transactions on Power Electronics | Year: 2015

In this letter, a quasi two-stage architecture is proposed for wide input voltage range (voltage ranges ≈ 1:2) and high step-down multiple output conversion. A dc-DCX, which operates as a dc-dc converter with regulated output when the input voltage is low and as a dc-dc transformer with unregulated output when the input voltage is high, is adopted in the first stage to provide optimized intermediate dc-bus voltages for the second-stage point-of-load converters. The input and output of the dc-DCX are in series and connected to the total input voltage. Hence, part of the input power is directly transferred to the intermediate bus without conversion. The devices' voltage stresses and the transformer turns ratio of the dc-DCX are reduced by using the proposed quasi two-stage architecture. Thus, the conversion efficiency is improved significantly. Furthermore, a dual-output LLC resonant converter with hybrid center-tapped and full-bridge rectifier is proposed for the dc-DCX to achieve high efficiency and high power density. A 100-W prototype with three outputs is built and tested to verify the analysis. © 2014 IEEE.

Chen X.,University of Electronic Science and Technology of China | Jia C.,University of Electronic Science and Technology of China | Wan Z.,University of Electronic Science and Technology of China | Zhang J.,Beijing Spacecrafts | Yao X.,Lanzhou University
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2014

Three phenothiazine-triphenylamine-based organic dyes (CD-1, CD-2 and CD-3) are designed based on the dye WD-8. The geometries, electronic structures, and electronic absorption spectra of these dyes before and after binding to TiO 2 are studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The calculated geometries indicate that these dyes show good steric hindrance effect which is advantage to inhibit the close intermolecular π-π aggregation effectively. The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels of these dyes could ensure positive effect on the process of electron injection and dye regeneration. The simulated spectra of CD-1∼3 show better absorption than that of WD-8 in the low energy zone. All the calculated results demonstrate that these dyes could be used as potential sensitizers for DSSCs and show better performances than WD-8. © 2013 Elsevier B.V. All rights reserved.

Zhang Y.,Taiyuan University of Technology | Zhang B.,Beijing Spacecrafts
Journal of Materials Science: Materials in Electronics | Year: 2014

The effect of grain size on the dielectric properties of MgO-TiO 2-ZnO-CaO ceramics is investigated. Attrition milling is chosen to obtain nanometre particle size from micrometre particle size powders. Additionally, the present study is focused on the effect of the nature of milling balls on εr, tanδ, and the temperature coefficient of capacitance (abbreviated as TCC). For that, three kinds of balls are tested: A1, A2 or A5 mm stabilised zirconia balls. For the samples milled by A2 mm balls for 10 h, the ceramics sintered at 1,270 °C showed favorable dielectric properties with εr = 22.6, tanδ = 1.3 × 10-5, and TCC = 19.1 ppm/°C. © 2014 Springer Science+Business Media New York.

Jia C.,University of Electronic Science and Technology of China | Zhang J.,University of Electronic Science and Technology of China | Zhang L.,Beijing Spacecrafts | Yao X.,Lanzhou University
Heterocycles | Year: 2011

A novel conjugated donor-acceptor compound (1) based on tetrathiafulvalene has been synthesized and fully characterized. Intramolecular charge transfer (ICT) in compound 1, arising from HOMO-LUMO singlet transitions, has been experimentally evidenced through absorption/fluorescence spectra and theoretical calculations. © The Japan Institute of Heterocyclic Chemistry.

Jia C.,University of Electronic Science and Technology of China | Zhang J.,University of Electronic Science and Technology of China | Zhang L.,Beijing Spacecrafts | Yao X.,Lanzhou University
New Journal of Chemistry | Year: 2011

The properties of two donor-acceptor compounds tetrathiafulvalene- acenaphtho[1,2-b] quinoxaline (1) and tetrathiafulvalene-3-nitro-acenaphtho[1,2- b]quinoxaline (2) have been investigated by solution-state studies (electrochemistry, absorption, self-assembly) and theoretical calculations (DFT, TD-DFT). The electrochemical studies indicate the nitro-substituted effect on their redox properties is negligible. Both compounds show effective intramolecular charge transfer (ICT) transitions in the UV-Visible range in solution. Compared with compound 1, compound 2 has a bathochromic shift in the absorption spectra, the λ max-ICT has been extended from 20800 cm -1 to 19700 cm -1 (480 nm to 507 nm). In addition, when the nitro group is employed, the self-assembly characteristics of the two compounds are substantially changed from ribbon-like nanostructures to root-like nanostructures. Density functional theory (DFT) calculations provide insights into their molecular geometries, electronic structures, and physico-chemical properties. © 2011 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

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