• 마이크로전자및패키징학회지
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• 제25권4호
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• pp.17-23
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• 2018

Recently, electric semiconductors became an issue because of efficient use of energy and compaction of electronics. Silicon electric semiconductors are difficult to put into it because of its physical limitations. Hence, the study of WBG (Wideband Gap) semiconductors like SiC and GaN began. These devices received attention because it can be miniaturized and worked at high temperatures over $300^{\circ}C$. WBG MOSFET electric semiconductors can show performance like silicon IGBT. This can solve the current problem of IGBT tail. The current study shows the technical principles and issues related to SiC and GaN power semiconductors. WBG devices can achieve high performance compared to silicon, but its performance can't be fully utilized because of lack in bonding technology. Therefore, this review introduces research on WBG devices and their packaging issues.

• 한국초전도ㆍ저온공학회논문지
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• 제11권1호
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• pp.30-34
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• 2009

This paper deals with charging and persistent-current mode operating characteristics of BSCCO magnet load using high-temperature superconducting (HTS) power supply. The HTS power supply consists of two heater-triggered switches, an iron-core transformer with the primary copper winding and the secondary BSCCO solenoid, and a BSCCO magnet load. The magnet load was fabricated by double pancake winding and its inductance is about 21 mH. A hall sensor was installed at the middle of the magnet load to measure the current in the load. In order to investigate the efficient pumping characteristics, operating tests of heater-triggered switch with respect to dc heater current were carried out, and the electromagnet current was determined by considering saturation characteristics of its iron core. The saturation characteristics of charged current in the magnet load were observed with respect to various pumping periods: 12 s, 14 s, 24 s and 32 s. After charging the magnet load, the persistent current was measured. The operating characteristics of the persistent current mode were mainly determined by joint resistance and magnet load.

• Journal of Power Electronics
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• 제16권4호
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• pp.1268-1276
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• 2016

A triode for alternating current (TRIAC) dimming light emitting diode (LED) driver, which adopts a variable switched capacitor for LED dimming and LED power regulation, is proposed in this paper. The proposed LED driver is power efficient, reliable, and long lasting because of the TRIAC switch that serves as its main switch. Similar to previous TRIAC dimmers for lamps, turn-on timing of a TRIAC switch can be controlled by a volume resistor, which modulates the equivalent capacitance of the proposed variable switched capacitor. Thus, LED power regulation against source voltage variation and LED dimming control can be achieved by the proposed LED driver while meeting the global standards for power factor (PF) and total harmonic distortion (THD). The long life and high power efficiency of the proposed LED driver make it appropriate for industrial lighting applications, such as those for streets, factories, parking garages, and emergency stairs. The detailed analysis of the proposed LED driver and its design procedure are presented in this paper. A prototype of 80 W was fabricated and verified by experiments, which showed that the efficiency, PF, and THD at V_s = 220 V are 93.8%, 0.95, and 22.5%, respectively; 65 W of LED dimming control was achieved with the volume resistor, and the LED power variation was well mitigated below 3.75% for 190 V < V_s < 250 V.

• KEPCO Journal on Electric Power and Energy
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• 제2권3호
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• pp.447-452
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• 2016

It is imperative to develop an effective pathway to depolymerize lignin into liquid fuel that can be used as a bioheavy oil. Lignin can be converted into liquid products either by a solvent-free thermal cracking in the absence air, or thermo-chemical degradation in the presence of suitable solvents and chemicals. Here we show that the solvent-assisted liquefaction has produced promising results in the presence of metal-based catalysts. The supercritical ethanol is an efficient liquefaction solvent, which not only provides better solubility to lignin, but also scavenges the intermediate species. The concentrated sulfuric acid hydrolysis lignin (CSAHL) was completely liquefied in the presence of solid catalysts (Ni, Pd and Ru) with no char formation. The effective deoxy-liquefaction nature associated with scEtOH with aid hydrodeoxygenation catalysts, resulted in significant reduction in oxygen-to-carbon (O/C) molar ratio up to 61%. The decrease in oxygen content and increase in carbon and hydrogen contents increased the calorific value bio-oil, with higher heating value (HHV) of $34.6MJ{\cdot}Kg^{-1}$. The overall process is energetically efficient with 129.8% energy recovery (ER) and 70.8% energy efficiency (EE). The GC-TOF/MS analysis of bio-oil shows that the bio-oil mainly consists of monomeric species such as phenols, esters, furans, alcohols, and traces of aliphatic hydrocarbons. The bio-oil produced has better flow properties, low molecular weight, and high aromaticity.

• 전력전자학회논문지
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• 제6권6호
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• pp.481-488
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• 2001

현재 AC-PDP(Plasma Disphay Panel) 의 기술은 급속히 발전하고 있는 추세이지만 아직도 몇가지 문제로 인해 이를 해결하기 위한 다각적인 접근이 이루어지고 있다. 동화상 윤곽의 제거 광(光) 대비 향상을 통한 화질의 개선 신뢰도 및 전력 효율을 개선하는 등의 문제가 여기에 해당되며 그 중에서도 특히 전력 효율의 관점에서 40 인치 이상의 대형화면을 지향한는 PDP 기술에서 가장 큰 약점으로 분류되고 있는 수백 와트(watt)에 이르는 전려 소모를 CRT 수준이 200[W] 미만으로 낮추어 것이 시급한 당면 과제이다. 전려 효율을 향상시키기 위해서 PDP의 발광효율을 높이는 것과 함께 기체 장번과는 직접적인 관련이 없이 구동과정시 발생하게 되는 불필요한 전력소모를 최소화 하여야 한다. 본 논문에서는 이러한 전력 소모를 최소화하기 위한 새로운 형태의 고효율 에너지 회수 회로를 제안하고 시뮬레이션을 통해 그 동작을 확인하였다. 또 이는 회로를 설제 7.5인치 패널에 인가하고, 200［kHz］에서 실험하여 제안한 고효율 에너지 회수회로의 타당성을 검증하였다.

• 동력기계공학회지
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• 제15권6호
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• pp.27-34
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• 2011

The increasing capabilities of the computers enable us to utilize various numerical schemes for the time-domain simulations concerned with 3-dimensional free-surface wave problems. There are still difficulties to solve such kind of problems, however. That's because long time simulations with large computational domain are needed in time-domain analysis. So, we need faster and more efficient numerical schemes to get the solutions practically for these problems. In this paper, a high-order spectral/boundary-element method is used for the numerical investigation of physics involved in wave-body interaction. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated and hydrodynamic forces also can be calculated in time-domain. To get the robust study in these topics, various numerical tests are performed and compared with others' works.

• 열처리공학회지
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• 제23권5호
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• pp.257-262
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• 2010

Recently, metal molding has become essential not only for automobile parts, but also mass production, and has greatly influenced production costs as well as the quality of products. Its surface has been treated by carburizing, nitriding and induction hardening, but these existing treatments cause considerable deformation and increase the expense of postprocessing after treatment; furthermore, these treatments cannot be easily applied to parts that requiring the hardening of only a certain section. This is because the treatment cannot heat the material homogeneously, nor can it heat all of it. Laser surface treatment was developed to overcome these disadvantages, and, when the laser beam is irradiated on the surface and laser speed is appropriate, the laser focal position is rapidly heated and the thermal energy of surface penetrates the material after irradiation, finally imbuing it with a new mechanical characteristic by the process of self-quenching. This research estimates the material characteristic after efficient and functional surface treatment using HPDL, which is more efficient than the existing CW Nd:YAG laser heat source.

• 열처리공학회지
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• 제22권6호
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• pp.339-344
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• 2009

Recently, Laser surface treatment technologies have been used to improve wear charactenitics and fatigue resistance of metal molding. When the laser beam is irradiated on the surface and laser speed is appropriate, the laser focal position is rapidly heated and the thermal energy of surface penetrates the material after irradiation, finally imbuing it with a new mechanical characteristic by the process of self-quenching. This research estimates the material characteristic after efficient and functional surface treatment using HPDL, which is more efficient than the existing CW Nd:YAG laser heat source. To estimate this, microstructural changes and hardness characteristics of three parts (the surface treatment part, heat affect zone, and parental material) are observed with the change of laser beam speed and surface temperature. Moreover, the depth of the hardened area is observed with the change of the laser beam speed and temperature. From the results of the experiments, it has been shown that the maximum hardness is approximately 788Hv when the heat treatment temperature and the travel speed are $1150^{\circ}$ and 2 mm/sec, respectively.

• 대한기계학회논문집B
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• 제33권8호
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• pp.580-588
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• 2009

This paper summarizes the experimentally-measured performance of small-scale, vertical-axis wind turbine for the purpose of improving the aerodynamic efficiency and its controllability. The turbine is designed to have a Savonius-Type rotor with an inlet guide-vane and an side guide-vane so that it achieves a higher efficiency than any lift- or drag-based turbines. The main design factors for this high-efficient, vertical wind turbine are the number of blades (Z), and the aspect ratio of Height/Diameter (H/D) among many. The basic model has the diameter of 580mm, the height of 464mm, and the blade number of 10. The maximum power coefficient of 0.50 was experimentally measured for the above-mentioned specifications. The inlet-guide vane ensures the maximum efficiency when the angle of attack to the rotor blade lies between $15^{\circ}$ and $20^{\circ}$. This experimental results for the vertical-axis wind turbine can be applied to the preliminary design of turbine output curve based on the wind characteristics at the proposed site by controlling its aerodynamic performance given as a priori.

• 한국전자통신학회논문지
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• 제17권1호
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• pp.173-180
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• 2022

근사 컴퓨팅은 효율적인 하드웨어 컴퓨팅 시스템을 설계하기 위한 유망한 방법이다. 근사 곱셈은 고성능, 저전력 컴퓨팅을 위한 근사 계산 방식에 사용되는 핵심적인 연산이다. 근사 4-2 compressor는 근사 곱셈을 위한 효율적인 하드웨어 회로를 구현할 수 있다. 본 논문에서는 저면적, 저전력 특성을 갖는 근사 곱셈기를 제안하였다. 근사 곱셈기 구조는 정확한 영역, 근사 영역, 상수 수정 영역의 세 영역으로 나누어진다. 새로운 4:2 근사 compressor를 사용하여 근사 영역의 부분 곱 축소를 단순화하고, 간단한 오류 수정 방식을 사용하여 근사로 인한 오류를 보상한다. 상수 수정 영역은 오차를 줄이기 위해 확률 분석을 통한 상수를 사용하였다. 8×8 곱셈기에 대한 실험 결과, 제안한 근사 곱셈기는 기존의 4-2 compressor 기반의 근사 곱셈기보다 적은 면적을 요구하면서 적은 전력을 소비함을 보였다.