• Journal of Power Electronics
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• 제12권3호
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• pp.458-467
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• 2012

Single phase converters suffer from ripple power pulsating at twice the line frequency. The ripple power is usually absorbed by a bulky capacitor bank and/or a dedicative LC resonant link, resulting in a low power density and a high cost. An alternative solution is using a dc link active power filter (APF) to direct the pulsating power into another energy-storage component. The main dc link filter capacitor can then be reduced substantially. Based on a mainstream dc APF topology, this paper proposed a new control strategy incorporating both dual-loop control and repetitive control. The circuit parameter design is also re-examined from a control point of view. The proposed APF scheme has better control performance, and is more suited for high power applications since it works in CCM and with a low switching frequency.

• ETRI Journal
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• 제35권5호
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• pp.900-910
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• 2013

Small-screen mobile terminals have difficulty accessing existing Web resources designed for large-screen devices. This paper presents an adaptive transformation method based on webpage semantic features to solve this problem. According to the text density and link density features of the webpages, the webpages are divided into two types: index and content. Our method uses an index-based webpage transformation algorithm and a content-based webpage transformation algorithm. Experiment results demonstrate that our adaptive transformation method is not dependent on specific software and webpage templates, and it is capable of enhancing Web content adaptation on small-screen terminals.

• 전력전자학회논문지
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• 제21권5호
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• pp.381-387
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• 2016

Many efforts have focused on the improvement of power density and efficiency by downsizing the motor and inverter. Recently, Toyota, Honda, and GM realized that the compact-sized motor uses the hairpin structure with increased space factor. Reducing the maximum torque from high-speed technique also makes it possible to design the high-power density model. Toyota and Honda used the newly developed power semiconductor IGBT to decrease conduction loss for high-efficiency inverter. In particular, Toyota used the boost converter to increase the DC link voltage for high efficiency in low-torque high-speed region. Toyota and GM also used the double-sided cooling structure for miniaturization of inverter for high-power density.

• Journal of Power Electronics
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• 제15권6호
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• pp.1421-1428
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• 2015

The efficiency and reliability of the dual-buck inverter (DBI) were greatly improved by eliminating the shoot-through problem and optimally designing the freewheeling diode. The traditional DBI suffers from large harmonic components with low output voltage and large capacity output filter inductor. To overcome the aforementioned disadvantages, a modified DBI (MBDI) was proposed by adopting a quasi-resonant link and pulse density modulation (PDM). This paper first introduces the working principle of the MBDI and PDM, and then the selection principle of system parameters is presented. Finally, a mathematical model of the MBDIis built, and an experiment prototype is set up. Simulation and experimental results verify the correctness of the theoretical analysis and the feasibility of the scheme.

• 대한교통학회지
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• 제13권4호
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• pp.79-103
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• 1995

The elasticity of a model is considered most important. Without showing the proper elasticity any model cannot provide useful information for decision making. This paper demonstrates a macro model which can generate dynamic transport informations every 15 minutes. Without the Wardrop principles and the monotonicity assumptions for the link travel time and link volume relationship, the basic elements of this new modeling approache are composed of link density simulation, stochastic incremental route choice, departure time choice, destination choice and mode choice. The elasticity of the proposed model is examined based on elasticity equations and simulation results. Also the transferability from a mega city like Seoul to a big city like Daejon is demonstrated for the choice model. The issues centering around the dynamic relations among density(k), speed(u), and flow rate(v) are also discussed for the modeling of highly congested situations.

• 전력전자학회논문지
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• 제26권2호
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• pp.120-126
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• 2021

DC-link capacitors are one of the main components in two-level three-phase voltage source inverters (VSIs); they provide the pulsating input current and stabilize the vacillating DC-link voltage. Ideally, the larger the capacitance of DC-link capacitors, the better the DC-link voltage stabilizes. However, high capacitance increases the cost and decreases the power density of VSI systems. Therefore, the capacitance should be chosen carefully on the basis of the DC-link voltage ripple requirement. However, the DC-link voltage ripple is dependent on the pulse-width modulation (PWM) strategy. This study especially presents a DC-link voltage ripple analysis when the minimum loss discontinuous PWM strategy is applied. Furthermore, an equation for the selection of the minimum capacitance of DC-link capacitors is proposed. Experimental results with R-L loads are also provided to verify the effectiveness of the presented analysis.

• Journal of Astronomy and Space Sciences
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• 제37권2호
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• pp.117-129
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• 2020

In a Satellite communication system, a link budget analysis is the detailed investigation of signal gains and losses moving through a channel from a sender to receiver. It inspects the fading of passed on data signal waves due to the process of spreading or propagation, including transmitter and receiver antenna gains, feeder cables, and related losses. The extent of the proposed tool is to make an effective, efficient, and user-friendly approach to calculate link budget analysis. It is also related to the satellite communication correlation framework by building up a graphical interface link analysis tool utilizing STK^® software with the interface of C# programming. It provides better kinds of graphical display techniques, exporting and importing data files, printing link information, access data, azimuth-elevation-range (AER), and simulation is also possible at once. The components of the link budget analysis tool include transmitter gain, effective isotropic radiated power (EIRP), free space loss, propagation loss, frequency Doppler shift, flux density, link margin, elevation plot, etc. This tool can be useful for amateur users (e.g., CubeSat developers in the universities) or nanosat developers who may not know about the RF communication system of the satellite and the orbital mechanics (e.g., orbit propagators) principle used in the satellite link analysis.

• ETRI Journal
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• 제34권1호
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• pp.122-125
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• 2012

A video signal through a high-density optical link has been demonstrated to show the reliability of optical link for high-data-rate transmission. To reduce optical point-to-point links, an electrical link has been utilized for control and clock signaling. The latency and flicker with background noise occurred during the transferring of data across the optical link due to electrical-to-optical with optical-to-electrical conversions. The proposed synchronization technology combined with a flicker and denoising algorithm has given good results and can be applied in high-definition serial data interface (HD-SDI), ultra-HD-SDI, and HD multimedia interface transmission system applications.

• 한국통신학회논문지
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• 제35권1B호
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• pp.68-77
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• 2010

무선 센서 네트워크는 다양한 환경에 분산되어 설치되며 무선 링크를 통하여 센싱된 데이터를 수집한다. 무선센서 네트워크에서 무선 링크의 품질은 환경적 요인이나 하드웨어의 성능에 따라 변화하는 특성을 갖는다. 링크 품질의 변화는 데이터의 손실을 야기 시킬 수 있으므로 링크 품질의 변화를 적응적으로 측정할 수 있어야 하며, 상위 계층인 경로 설정 프로토콜에서는 이를 고려해야 한다. 본 논문에서는 대규모 무선 센서 네트워크에서의 적응적 링크 품질 측정 및 경로 설정 기법을 제안한다. 제안한 기법은 링크의 품질이 불안정할 때 민첩하게 링크의 품질을 측정하여 새로운 경로를 선택하고 링크의 품질이 안정할 때 간헐적으로 링크 품질을 측정하여 에너지 소모를 줄인다. 또한 높은 밀집도의 네트워크에서는 오버헤드를 줄이기 위해 적은 수의 비컨을 사용하며, 낮은 밀집도에서는 많은 수의 비컨을 사용하여 품질이 좋은 링크를 경로로 설정함으로써 패킷 손실률을 개선한다. 실험을 통하여 제안한 방법이 신뢰성 및 에너지효율성 향상시킬 수 있음을 확인하였다.

• Composites Research
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• 제22권3호
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• pp.35-43
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• 2009

본 연구에서는 카본블랙이 충전된 ethylene-propylene dine monomer(EPDM) 고무에 대한 가교밀도 측정법을 확립하고 EPDM 고무호스에 대해 열가속 및 산소스트레스를 가하여 가교밀도 변화를 측정하였다. 노화 초반에는 산화황가교의 형성으로 고무의 가교밀도측정값이 약간 저하하였다가 노화시간이 지남에 따라 일부 미반응 황 분자들의 가황반응으로 추가적인 가교 결합을 형성하면서 가교밀도측정값은 점차 증가하였다. 이들 가교밀도 변화거동은 인장강도의 거동과 유사하였다. $180^{\circ}C$의 고온노화에서는 노화시간이 길어짐에 따라 노화에 따른 가교밀도의 증가폭은 그다지 크지 않았으나, 인장강도와 신장률은 크게 저하하였다. 즉, 온도가 높을 수록 EPDM 고무의 가교밀도의 변동보다는 EPDM 분자사슬에서의 산화물(carbonyl groups) 형성과, 가교점의 산화황 생성으로 기계적 물성의 열화가 일어난 것이다.