• 전력전자학회논문지
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• 제19권5호
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• pp.407-414
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• 2014

This study proposes a control design for the grid output current and for reducing the neutral-point voltage oscillation through the small-signal modeling of the three-phase grid connected with a three-level neutral-point-clamped (NPC) inverter with LCL filter. The three-level NPC inverter presents an inherent problem: the neutral-point voltage fluctuation caused by the neutral-point current flowing in or out from the neutral point. The small signal modeling consists of averaging, dq0 transformation, perturbing, and linearizing steps performed on a three-phase grid connected to a three-level NPC inverter with LCL filter. The proposed method controls both the grid output and neutral-point currents at every switching period and reduces the neutral-point voltage oscillation. The validity of the proposed method is verified through simulation and experiment.

• 전기학회논문지
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• 제66권5호
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• pp.778-785
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• 2017

This paper presents a control method for reducing the distortion of the grid current at a grid-connected three-level neutral point clamped (NPC) inverter. The grid current is distorted from the 5th and 7th harmonic components in the stationary frame current also the 6th harmonic component in the synchronous frame current. In this paper, the 6th harmonic component on synchronous frame is controlled by using all-pass filters (APFs) and proportional integral (PI) controllers for distortion of the grid side. When transformed the 6th harmonic component is controlled, the 5th and 7th harmonic components are reduced. The validity of the proposed control method is verified by simulation and experiment results using a 25kW three-level NPC inverter.

• 인터넷정보학회논문지
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• 제3권4호
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• pp.27-36
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• 2002

본 논문은 원격 교육 시스템(FVU)을 위하여 벡터이미지를 적용한 에디터를 개발하였다. 이 에디터를 사용하여 교수자는 화면상에서 자체 페이지를 효율적으로 구성할 수 있고, 파일의 크기를 줄일 수 있으며, 이미 제작된 이벤트들을 수정한 수도 있다. VUEditor라 명명된 이 에디터는 UML방법론을 적용하여 개발하였다. VUEditor는 강의에 필요한 첫 화면을 구성할 수 있으며, 이렇게 제작된 강의안은 Vector변환을 통해서 VUAuthor로 익스포트(Export)된다. 이러한 과정을 통하여, 파일 사이즈를 감소시키며, 낮은 대역폭을 형성하게 한다. 이러한 설계는 결과적으로 이미지 툴 이나 파워포인트와 같은 응용 프로그램 없이도 강의에 필요한 첫 화면을 VUEditor 자체적으로 구성하며, 결과 파일의 크기가 작아지므로 네트워크 트래픽의 문제를 다소 해결해준다.

• 한국경영과학회지
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• 제42권2호
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• pp.35-48
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• 2017

As the technology convergence paradigm emerges, the need for "CIA techniques" to analyze the mutual effects of technology is increasing. However, since the CIA input parameter estimation is difficult, the present study suggests a "CIA input parameter setting model" to alleviate the difficulty of CIA input parameter estimation. This paper is focused on the difference of measurement difficulty by each scale which expert's estimation behavior was defined as measurement activity quantifying the judgment of future technology. Therefore, this model is designed to estimate the input variable as a sequence or isometric scale that is relatively easy to measure, and then converts it into a probability value. The input parameter setting model of the CIA technique consists of three sub-models : 'probability value derivation model', 'influence estimation model', and 'impact value calculation model', in order to develop a series of models the Thurstone V model, Regression Analysis, etc has been used.

• Journal of Power Electronics
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• 제12권4호
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• pp.548-558
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• 2012

In this paper, a novel offset-based single-state pulse width modulation (PWM) method for achieving zero common-mode voltage (CMV) and reducing switching losses in multilevel inverters is presented. The specific active switching state of the zero common-mode (ZCM) voltage that approximates the reference voltage can be deduced from the switching state sequence of the reduced CMV phase disposition PWM (CMV PD PWM) method. From the reference leg voltages for the zero common-mode voltage, an N-to-2-level transformation defines a virtual two-level inverter and the corresponding nominal leg voltage references. The commutation process of the reduced CMV PD PWM method in a multilevel inverter and its outputs can be simply followed in a nominal switching time diagram for the virtual inverter. The characteristics of the reduced CMV PD PWM and the single-state PWM for zero common-mode voltage are analyzed in detail in this paper. The theoretical analysis of the proposed PWM method is verified by experimental results.

• International Journal of Control, Automation, and Systems
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• 제1권4호
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• pp.495-502
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• 2003

This paper focuses on the implementation of an efficient tracking method of a moving object using optimal representative blocks by way of a pan-tilt camera. The key idea is derived from the fact that when the image size of a moving object is shrunk in an image frame according to the distance between the mobile robot camera and the object in motion, the tracking performance of a moving object can be improved by reducing the size of representative blocks according to the object image size. Motion estimations using Edge Detection (ED) and Block-Matching Algorithm (BMA) are regularly employed to track objects by vision sensors. However, these methods often neglect the real-time vision data since these schemes suffer from heavy computational load. In this paper, a representative block able to significantly reduce the amount of data to be computed, is defined and optimized by changing the size of representative blocks according to the size of the object in the image frame in order to improve tracking performance. The proposed algorithm is verified experimentally by using a two degree-of- freedom active camera mounted on a mobile robot.

• 한국컴퓨터정보학회논문지
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• 제8권4호
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• pp.111-116
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• 2003

본 논문은 저전력 레지스터 전송 단계 설계를 위한 최적 클럭 주기 선택 알고리듬을 제안한다. 제안한 알고리듬은 전력 소비를 최소화하기 위하여 시스템의 성능을 향상시킨 후에 공급 전압을 줄임으로써 처리율을 유지하는 방법을 사용한다. 본 논문은 구조의 변환 중에서 파이프라인을 이용한 저 전력을 선택한다. 또한 제안한 알고리듬은 자원 공유를 최대화하기 위해 클럭 주기 선택이 중요하다. 본 알고리듬은 최적 클럭 주기 선택 알고리듬을 수행한다. 실험결과에서는 상위 레벨 벤치마크 상에서 AR 필터와 HAL 필터는 동일한 결과를 얻을 수 있고, EL 필터인 경우 2파이프 단계에서는 10.5%, 3 파이프 단계에서는 무려33.4% 클럭 주기 감소를 얻을 수 있다.

• 통상정보연구
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• 제10권1호
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• pp.97-115
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• 2008

This paper is to review how Korean trading companies perform and promote the digital transformation through the e-networking with global market, and how much they extend the volume of export, and make the company grow inward or outward in order to enhance the effects of economic growth in Korea. It is suggested that global agreement on e-Trade(or u-Trade) should be made in order to expand the global e-networking practices and to ensure transferring of transport documents(or business documents). Moreover, it also suggested that networking on the global trading partners such as government authorities, diplomatic offices abroad, overseas Koreans, students studying abroad, Korean merchants abroad, etc. should be made in single window for improving and upgrading the image of Korean trading companies. By making of global e-network platform between overseas business partners, trading companies are able to expect various synergy effects such as improving the satisfaction of their customers, promoting the global transactions, reducing the operation and transaction cost, helping fording overseas buyers, and extending export volume and sales profit, etc. Customers can also obtain the information about trading goods easily and rapidly, and cut down the transaction stage using information exchange with partners. All of the trading partners in the world can maintain their business partnership as long as they use the global e-network.

• 자원환경지질
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• 제33권5호
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• pp.353-365
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• 2000

After their first appearance on Earth, bacteria have exerted significant influence on geochemical behavior of elements. Numerous evidence of their control on geochemistry through geologic history has been observed in a variety of natural environments. They have mediated weathering rate, formation of secondary minerals, redox transformation of metals and metalloids, and thus global cycling of elements. Such ability of bacteria receives so considerable attention from microbiologists, mineralogists, geologists, soil scientists, limnologists, oceanographers, and atmospheric scientists as well as geochemists that a new and interdisciplinary field of research called 'geomicrobiology' is currently expanding. Some recent subjects of geomicrobiology which are studied extensively are as follows: 1) Functional groups distributed on bacterial cell walls adsorb dissolved cations onto cell surfaces by electrostatic surface complexation, which is followed by hydrous mineral formation. 2) Dissimilatory metal reducing bacteria conserve energy to support growth by oxidation of organic matter coupled to reduction of some oxidized metals and/or metalloids. They can be effectively used in remediating environments contaminated with U, As, Se, and Cr. 3) Bacteria increase the rate of mineral dissolution by excreting proton and ligands such as organic acids into aqueous system. 4) Thorough investigation on the effects of biofilm on geochemical processes is needed, because most bacteria are adsorbed on solid substrates and form biofilms in natural settings.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 1999년도 추계학술발표회
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• pp.81-84
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• 1999

The aqueous geochemical characteristics of Cr(III) and Cr(Ⅵ) in environmental systems are very different from one another: Cr(Ⅵ) is highly soluble, mobile and toxic relative to Cr(III) Reduction of Cr(Ⅵ) to Cr(III) are beneficial in aquatic systems because of the transformation of a highly mobile and toxic species to one having a low solubility in water, thus simultaneously decreasing chromium mobility and toxicity. Fe(II) species are excellent reductants for transforming Cr(Ⅵ) to Cr(III), and in addition, keeping Cr(III) concentrations below the drinking water standard of 52 ppb at pH values between 5 and 11. Investigations of the effects of NOM on Cr(Ⅵ) reduction are for examining the feasibility of using ferrous iron to reduce hexavalent chromium in subsurface environments. Experiments in the presence of soils, however, showed that the solid phase consumes some of the reducing capacity of Fe(II) and makes the overall reduction kinetics slower. The soil components bring about consumption of the ferrous iron reductant. Particular attention is devoted to the complexation of Fe(II) by NOM and the subsequent effect on Cr(Ⅵ) reduction. Cr(Ⅵ) reduction rate by Fe(II) was affected by the presence of NOM (humic acid), The effects of humic acid was different from the solution pH values and the concentration of humic acid. It was probably due to the reactions between humic acid and Cr(Ⅵ), humic acid and Fe(II), and between Cr(Ⅵ) and Fe(II), at each pH.