• Journal of Energy Engineering
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• v.14 no.1
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• pp.37-45
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• 2005

The fuel cell system is one of very useful energy sources. The system has advantages as renew-able and environmental sources. To obtain AC electricity from fuel cells, inverters are necessary. A multilevel converter is used as an inverter for a high power fuel cell system. Through harmonic analysis, it is shown that the harmonic components and THD increase while fundamental component decreases as voltage sag increases. To solve the voltage sag problems, three different approaches are investigated in this paper; installation of a boost converter at the fuel cell output, control of pulse widths, and use of ultracapacitors. The proposed three approaches are analyzed and compared using simulation and experimental results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.327-327
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• 2010

자동차에서 실내음질은 구매결정 요소들 중의 하나로 그 중요성이 점차 증가하고 있다. 따라서 다양한 운전조건에서 운전자가 기대하는 실내음질의 기대 수준을 충족시켜야 한다. 소비자는 운전경험과 습관에 따라 기대하는 음질에 차이가 있고 소리에 대한 표현방식도 모호하기 때문에 이러한 주관적 특성을 하나의 통일된 표현으로 정의 하기가 어렵다. 그러나 지난 이십여 년 동안의 음질개발과 차량 실내소음 주관평가의 통계처리로 통일된 표현을 할 수 있었다. 나아가 심리음향학 및 신호처리기술의 발달과 꾸준한 음질연구결과로 소리특성을 객관적으로 나타내는 소리의 시각화가 가능하였으며, 운전자가 인식하는 주관평가와의 상관관계를 높여 차량의 대표적인 음질인자로 정량화하여 음질목표를 설정할 수 있었다. 실내소음의 구성은 엔진 투과음, 흡배기 소음, 바람 소음, 도로 기인 소음 등으로 다양하므로 소음원에 따라 음의 균형을 맞추어 조화로운 음질개발을 하는 것이 중요했다. 또한 차량 판매되는 지역에 따라 선호음이 상이하여 지역별 실내음질의 차별화가 필요했다. 궁극적으로는 운전자의 감성품질을 만족할 수 있도록 음을 제어하여 브랜드 사운드를 개발하고 있다. 이러한 실내음질을 달성하기 위한 방법으로 소음원과 전달경로에 대해 기여도를 분석하고, 경로를 구성하는 시스템 별로 세분화하여 시스템 목표를 설정하였다. 시스템 개발에 중요한 인자로 차량의 동강성 및 흡차음 성능을 들 수 있다. 특히 디젤차량의 비중이 큰 유럽업체의 차량의 동강성 및 흡차음 개발 능력은 높게 평가되고 있다. 이에 유럽의 부품전문회사가 가지고 있는 해석과 시험적인 개발 방법을 통하여 전달계 특성을 만족하기 위한 시스템의 동강성 및 흡차음 특성을 개발하고 있다. 차량음질 튜닝의 중요한 기법 중 하나로 흡배기 개발을 추진하고 있다. 친환경자동차인 하이브리드차량, 전기차량 및 연료전지차량의 경우 전기구동부품에서 발생하는 각종 이음 발생을 최소화 했다. 보행자를 보호하고 운전의 즐거움을 향상하기 위한 가상사운드 개발을 진행하고 있다. 회사 수익성 향상을 위한 원가절감 및 구조 경량화에 따른 음질악화와 연비 향상 및 배기가스 규제 강화로 고성능 고출력 엔진탑재에 따른 음질악화 요인을 극복해야 했다. 운전자의 청감은 차량의 운전성에 따라서도 크게 영향을 받게 되므로 엔진제어와 변속기제어를 통해 음질과 운전성이 조화를 이룰 수 있도록 개발하고 있다. 향후, 소음원에 따른 시스템 최적화 개발, 운전성과 음질 연계 개발과 친환경차량의 가상사운드 개발 등이 자동차 음질 개발의 중요한 이슈로 생각한다.

• Food Science of Animal Resources
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• v.29 no.1
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• pp.82-90
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• 2009

This study was carried out to evaluate the effects of microwave power level on cooking properties of ground pork patties (fat level: 20%). Each patty was cooked from a thawed state to $76.7^{\circ}C$ (center temperature) in a microwave oven with power levels of 40% (360 W), 60% (540 W), 80% (720 W), and 100% (full power, 900 W), respectively. Cooking rate increased with power level, and the non-uniformity also increased with time during cooking. Overheating at the edge of the patties was observed for all power levels, and maximum temperature differences in between the edge position and center position were found in patties cooked at the 900 W power level. Compositional properties, total cooking loss, and drip loss were not affected by power level, although moisture content was lower at the edge than at the center position. As the power level increased, the reduction in patty diameter of cooked patties increased while the reduction in patty thickness decreased. Pork patties cooked at lower power levels (360 W and 540 W) had higher shear force values than those cooked at higher power levels (720 W and 900 W). Few changes were observed in instrumental color values.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.8
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• pp.1773-1779
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• 2015

Shore-to-sea visible light communication using color clustered multiple-input and multiple-output (MIMO) is presented. The proposed maritime visible light communication (MVLC) offers a low-cost, high-speed wireless link for shore-to-sea maritime communications. Each color cluster is comprised of 50 red, green and blue (RGB) light emitting diodes (LEDs) and is modulated using on-off-keying (OOK). Selection combining is performed at the receiver, producing diversity effect within that color cluster. In this paper, we employ sea states (wave height, wind speed, etc.) data from both Pierson-Moskowitz and JONSWAP spectrum models under atmospheric turbulence conditions. Based on the simulation model, the maritime link quality is analysed in terms of coverage distance and bit error rate performance. The results show that the proposed system provides an efficient MVLC, while satisfying International Association of Lighthouse Authorities (IALA) requirements for maritime buoyage system and also offering sufficient illumination from high power LEDs.

• Journal of Korean Society for Geospatial Information Science
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• v.17 no.2
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• pp.123-131
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• 2009

The telecommunication technology in the 21st century has come up to the standard which could transmit various spatial information by means of on-line and the printing technology using computers has been on a par with presswork in quality. In addition, map users also would like to get various spatial information through on-line directly or indirectly. None the less, the supply system of national base map in our country has maintained the off-line sales method. It is owing to this reason that the nation's supply system has shown a high degree of inefficiency from the viewpoint of the inventory control, rapidity, and economical efficiency as compared with the on-line sales system in the developed countries. This study tried to analyze some problems of the present supply system in order to build up the foundation of the efficient map supply system and also developed the system such as On-demand maps, on-line paying and sales, inventory control, meta dat establishment, and security module, etc. This study tried to analyze some problems of the present supply system in order to build up the foundation of the efficient map supply system and also developed the system such as On-demand maps, on-line paying and sales, inventory control, meta dat establishment, and security module, etc.

• Journal of Korea Society of Industrial Information Systems
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• v.21 no.3
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• pp.29-33
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• 2016

Development of the distributed energy resources such as photovoltaic, wind, and fuel cell has increased rapidly due to the rising demand for clean energy utilization. On the other hand, the distribution system became complex and has problems such as degradation of power factor and current unbalance caused by power converters, reactive power and unbalanced loads. To solve these problems, this paper proposes a 3-phase 4-leg type power conditioning system with compensation control algorithm for the reactive power and unbalance current in distribution system using photovoltaic resource. It is simulated in PSCAD/EMTDC and the effectiveness is confirmed.

• Journal of the Korean Society for information Management
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• v.20 no.2
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• pp.93-112
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• 2003

A public information system is being expanded, along with the advance of information technology, to strengthen national competitiveness and provide people with better services. And there also is a growin need for the better performance of that system, as a tremendous amount of public financial resources is invested in that. To address that need, it's required to make an evaluation of its efficiency on a regular basis to identify its problems and make it work better. The purpose of this study was, accordinglu, to examine the quality of data and services provided by the Work-Net, a Web-based public employment information system. The subjects in this study were 102 users of it, and the system was evaluated in terms of content, accuracy, timeliness, display format, ease of use and customer support. For data analysis, t-test and one-way ANOVA were implemented to find out the general characteristics of the users, and to see Whether or not their view was different according to the type of information they searched for. The findings of this study are expected to lay some foundation for intensifying the efficiency of the public and private employment information systems.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.5
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• pp.39-43
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• 2020

In this paper, we propose the multi-channel interference cancellation algorithm for visible light communication (VLC) in smart building. The VLC system is communication technology using visible rays that come out in Light Emitting Diode (LED) device. It has energy curtailment effect and possible to use in ubiquitous network service applications. When a large number of users communicate indoors, the performance can be reduced due to channel interference. To remove interference, at the first, the minimum mean square error (MMSE) scheme as interference cancellation methods used, and then the successive interference cancellation (SIC) is applied to obtain additional diversity gain and improve interference cancellation performance. Indoor VLC channel model is employed. The performance is evaluated in terms of bit error rate (BER). From the simulation results, it is confirmed that the proposed scheme has better BER performance compared to the previous systems. As a result, the proposed interference cancellation improves the signal quality of VLC systems by effectively removing the channel noise. The results of the paper can be applied to VLC for smart building and general communication systems.

• Journal of IKEEE
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• v.24 no.1
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• pp.170-177
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• 2020

This paper presents an open-fault tolerance control method for active neutral point clamped (ANPC) inverter with high frequency/low frequency (HF/LF) modulation. By applying the ANPC inverter with SiC MOSFETs and Si IGBTs, the system efficiency and performance can be improved compared to a Si-based inverter. HF/LF modulation is used for a megawatt-scale inverter to minimize the commutation loop. The open-switch failure in megawatt-scale inverter causes severe damage to load and huge expenses when the inverter has been shut-down. The proposed tolerance control of open-switch failure provides continuous operation and improved reliability to the ANPC inverter. The effectiveness of the proposed fault tolerance control is verified by simulation results.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.10
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• pp.1867-1872
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• 2016

In the area of digital signal processing, it is necessary to improve the quality of the speech signal after removing the background noise which exists in a various real environments. The important thing to consider when removing the background noise acoustically is that to solve the problem, depending on the information of the human auditory mechanism is mainly the amplitude spectrum of the speech signal. This paper introduces the characteristics of a frequency-weighted spectrum shaping filter for the extraction of the amplitude spectrum of the speech signal with the primary purpose. Therefore, this paper proposes an algorithm using the methods of a Wiener filter and the frequency-weighted spectrum shaping filter according to the acoustic model, after extracted the amplitude spectral information in the noisy speech signal. The spectral distortion (SD) output of the proposed algorithm is experimentally improved more than 5.28 dB compared to a conventional method.