• 항공우주기술
• /
• 제10권2호
• /
• pp.56-64
• /
• 2011

최근 위성 시스템의 전력분배는 기존의 퓨즈와 릴레이로 구성된 것과는 달리 LCL(Latching Current Limiter) 회로로 구현되어, 각각의 부하전원을 단속한다. LCL은 부하에서 생기는 과전류를 제한함으로서 고장 의심이 있는 부하를 물리적으로 차단하는 기존 방법에 비하여 고장의 원인을 분석하고, 일시적인 고장인 경우 부하를 재사용할 수 있는 장점이 있다. 그러나 LCL 회로는 전자소자로 구현되는 만큼 주변회로(부하회로)와의 연동성과 회로 자체의 특성을 이해해야 하며, 무엇보다 과전류를 차단하기 위하여 설정하는 LCL 동작 파라미터의 정의를 위한 기술적인 접근이 요구된다. 따라서 본 논문에서는 전력분배 모듈의 LCL 동작 파라미터를 정의하기 위한 분석을 수행했고, 회로구현 및 특성 시험결과를 나타냈다.

• 한국철도학회논문집
• /
• 제20권4호
• /
• pp.466-473
• /
• 2017

최근 국내 철도 관련 기관에서 고속집전용 판토그래프를 개발하고 있으며, 이는 상부암의 경량화를 위하여 기존의 강재(Steel) 대신에 CFRP(Carbon Fiber Reinforced Plastics)와 알루미늄의 혼성구조체를 적용한 구조를 갖는다. KTX-산천 열차의 경우, 한 대의 판토그래프를 통해서 열차에 필요한 모든 전력을 공급해야 하는 동력집중식이므로 판토그래프는 큰 통전 용량을 가져야 한다. 하지만, 알루미늄 파이프의 열적 특성 분석 없이 통전 용량을 증대시키기 위하여 파이프의 두께를 임의로 증가시키게 되면 상부암의 무게 증가로 집전성능의 저화를 초래할 수 있다. 따라서, 본 논문에서는 KTX-산천 열차의 정지 상태에서 수전 시 판토그래프 상부암 혼성구조체를 이루는 알루미늄 파이프의 시간 경과에 따른 온도 특성 변화를 열해석을 통하여 분석하고, 제시된 판토그래프 통전 용량에 부합되는 알루미늄 파이프의 최소 두께의 적정성을 검토하고자 한다.

• JSTS:Journal of Semiconductor Technology and Science
• /
• 제2권1호
• /
• pp.59-69
• /
• 2002

A semi-analytical model based on exact numerical analysis of the 2DEG channel in pseudo-morphic HEMT (PMHEMT) is presented. The exactness of the model stems from solving both Schrodinger's wave equation and Poisson's equation simultaneously and self-consistently. The analytical modeling of the device terminal characteristics in relation to the charge control model has allowed a best fit with the geometrical and structural parameters of the device. The numerically obtained data for the charge control of the channel are best fitted to analytical expressions which render the problem analytical. The obtained good agreement between experimental and modeled current/voltage characteristics and small signal parameters has confirmed the validity of the model over a wide range of biasing voltages. The model has been used to compare both the performance and characteristics of a PMHEMT with a competetive HEMT. The comparison between the two devices has been made in terms of 2DEG density, transfer characteristics, transconductance, gate capacitance and unity current gain cut-off frequency. The results show that PMHEMT outperforms the conventional HEMT in all considered parameters.

• Journal of Electrical Engineering and Technology
• /
• 제13권3호
• /
• pp.1275-1284
• /
• 2018

The coaxial magnetic gear with the flux concentrating structure is known that it has the torque performance advantage over the coaxial magnetic gear having surface mounted permanent magnet, thanks to the flux focusing effect. But, if the solid cores are used in the modulating pieces and rotor cores to consider the mechanical reliability and cost reduction, the operating torque of the flux concentrating coaxial magnetic gear can be significantly diminished because the iron losses at the solid cores affect the actual transmitted torque. Furthermore, the modulating pieces and rotor cores have different characteristics of the iron losses from one another, because the space harmonic components of the magnetic flux density, which cause the iron losses, are different. Thus, in this paper, we focused on the analysis of the characteristics of the space harmonic components of the magnetic flux density and resultant eddy current losses in the surface mounted PM and flux concentrating coaxial magnetic gears, when these coaxial magnetic gears have the solid cores at the modulating pieces and rotor cores. The characteristics of pull-out torque (static torque), operating torque (dynamic torque), and efficiency are also researched, and compared by the 3D finite element analysis (FEA) and experiment.

• 한국광학회지
• /
• 제19권5호
• /
• pp.381-385
• /
• 2008

InGaN/Sapphire LED에서 기판 제거와 패키지 방식이 광출력 특성에 미치는 영향을 분석하였다. Sapphire 기판의 제거는 반도체 접합에서 발생된 열의 방출에 도움이 되지만, 반대로 광추출효율이 손상되는 문제점이 수반된다. Sapphire 기판이 제거된 칩을 열전도율이 좋은 금속의 마운트 위에 부착하면, 최대 구동전류는 현저히 증가하고 광출력도 상당히 증가됨으로써, 광추출효율이 손상되는 문제점이 어느 정도 보상된다. 하지만, sapphire 기판이 제거된 칩을 상대적으로 열전도율이 낮은 유전체의 마운트 위에 부착하는 경우에는, 거의 모든 입력전류 범위에서 sapphire 기판이 남아 있는 일반형 칩보다 낮은 광출력을 나타낸다. 따라서, 작은 광출력이 요구되는 응용분야에서는 사용된 칩 마운트의 종류에 무관하게, 일반형 칩이 sapphire 기판이 제거된 칩 보다 유리한 것으로 분석된다.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2016년도 전력전자학술대회 논문집
• /
• pp.75-76
• /
• 2016

This paper proposes a power factor correction circuit with a high efficiency over a wide load range characteristics for a communication power supply. And the characteristic verification is applied to produce a design of prototype. Power factor correction circuit can reduce conduction losses by applying Bridgeless Boost Converter for efficiency. Over a wide load range to maintain the efficient, the control method of a PWM controller is divided by two sections according to the load area. In the low-load region, it was reduced switching losses by applying the critical conduction mode control method. On the other hand, in the heavy-load area, the hysteresis current control method is used to maintain the high efficiency over a wide load range by limiting the peak noise of the inductor.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
• /
• pp.30-33
• /
• 2005

Though sensible heat flux is one of heat flux components, it is generally considered that the importance is low compared with other components because of the small value. Actually sensible heat flux over the tropical ocean is extremely small, less than $100\;W/m^2$ .. However, it should be noted that sensible heat flux in boreal winter over the western boundary current regions is considerably large, about $100\;W/m^2$, and not neglected. In this study we carry out intercomparison of various global sensible heat flux data including not only satellite-derived data but also reanalysis data in order to clarify the characteristics of those data.

• Child Studies in Asia-Pacific Contexts
• /
• 제4권1호
• /
• pp.65-76
• /
• 2014

This study aims to explore the characteristics of translated picture books in South Korea and their cultural meanings over a five-decade period. This time can broadly be divided into three periods, being the Settlement Period (pre-1990), the Flourishing Years (1991-2000) and Globalization (post-2001). During the Settlement Period, picture books in South Korea were derived mainly from Japan and America and tended to be informational in nature or based on folk tales. These were translated into Korean to meet the public's curiosity for foreign cultures or for scientific information. The Flourishing Years were characterised by the availability of picture books on a wide variety on themes and forms from all over the world. In this period, the translation of books into Korean focused on a literal rendition of the meanings and sounds of names from the original text. There was also a proliferation of audiotapes, videos and TV programs based on famous picture books. In the current period of Globalization, Korean publishers, who have built confidence through studying foreign picture books over time, have increased efforts to produce their own picture books and export them abroad.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
• /
• pp.18-21
• /
• 2008

Lee (2008) proposed the pansharpening method to reconstruct at the higher resolution the multispectral images which agree with the spectral values observed from the sensor of the lower resolution values. It outperformed over several current techniques for the statistical analysis with quantitative measures, and generated the imagery of good quality for visual interpretation. However, if a small object stretches over two adjacent pixels with different spectral characteristics at the lower resolution, the pixels of the object at the higher resolution may have different multispectral values according to their location even though they have a same intensity in the panchromatic image of higher resolution. To correct this problem, this study employed an iterative technique similar to the image restoration scheme of Point-Jacobian iterative MAP estimation. The effect of pansharpening on image segmentation/classification was assessed for various techniques. The method was applied to the IKONOS image acquired over the area around Anyang City of Korea.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2002년도 하계학술대회 논문집 C
• /
• pp.1717-1720
• /
• 2002

Electrodeless discharge lamps have been objects of interest and research for several decades, mainly because of their potential for extremely long life, high lamp efficacies and smaller than standard fluorescent lamps size. A series of measurements and observations concerning variables has yielded optical and electrical characteristics for electrodeless discharge lamp like incandescent lamp and circular lamp feature. Last experiment were carried out to determine the lamp temperature at several surface points during operation. Light output levels in excess over 60,000 cd/$m^2$ have been measured in electrodeless discharge lamp for a general of conditions. At lamp surface temperatures have been measured over $80^{\circ}C$, and starting current have been measured over ${\sim}A$.