• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.3
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• pp.242-249
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• 2011

The proposed converter has easy device selection for high step-up and high power applications since boost half bridge and voltage doubler cells are connected, respectively, in parallel and series in order to increase output power and voltage. Especially, optimized design of high frequency transformers is possible owing to reduced turn ratio and eliminated dc offset, and distributed power through three cores is beneficial to low profile and thermal distribution. The proposed converter does not necessitate start-up circuit and additional clamp circuit due to the use of whole duty range between 0 and 1 and is suitable for applications with wide input voltage range. Also, high efficiency can be achieved since ZVS turn on of switches are achieved in wide duty cycle range and ZCS turn on and off of diodes are achieved. The proposed converter was validated through 5 kW prototype.

• The Journal of Information Technology
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• v.6 no.2
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• pp.1-8
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• 2003

This paper is about power line communication(PLC) over the low power voltage grid. The main advantage with power line communication is the use of an existing infrastructure. The PLC channel can be modeled as having multi-path propagation with frequency-selective fading, typical power lines exhibit signal attenuation increasing with length and frequency. OFDM(Orthogonal Frequency Division Multiplexing) is a modulation technique where multiple low data rate carriers are combined by a transmitter to form a composite high data rate transmission. To implement the multiple carrier scheme using a bank of parallel modulators would not be very efficient in analog hardware. Each carrier in an OFDM is a sinusoid with a frequency that is an integer multiple of a base or fundamental sinusoid frequency. Therefore, each carrier is a like a Fourier series component of the composite signal. In fact, it will be shown later that an OFDM signal is created in the frequency domain, and then transformed into the time domain via the Discrete Fourier Transform(DFT).

• The Journal of Engineering Geology
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• v.18 no.2
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• pp.215-225
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• 2008

In order to investigate the influence factors to compressive and tensile strength of basalt in Cheju Island, rock samples of Pyosenri basalt, trachy-basalt and scoria were taken from Seoguipo-Si Seongsan-Eup area, and a series of uniaxial compressive strength test and Brazilian test were carried out. Especially, these tests were performed in consideration of the loading speed, the moisture content in rock sample, and the anisotropy of rock strength. The uniaxial compressive strength was increased gradually as the loading speed rose. The increasing quantity of uniaxial compressive strength had a difference in each rock types. Also, the strength was decreased with increasing the moisture contents in rock sample by pore water. As the result of test considering the anisotropy of rock strength, the compressive strength in condition of failure occurred parallel to stratified layer is decreased about 12-26% more than that in condition of failure occurred inclined to stratified layer.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.6
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• pp.1055-1061
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• 2000

The kinetics of tar formation has been studied experimentally and modeled mathematically for waste lubricating oil after pyrolyzed at batch reactor. And stabilization of pyrolyzed oil has been studied. A combination of series and parallel reaction was assumed for the mechanism of tar formation. From the proposed kinetic model, pyrolyzed oil to tar was found to be rate limiting step for tar formation. It was found that the fly ash and coke had the ability to remove materials of tar formation and to protect oxidation of pyrolyzed oil.

• Korean Journal of Environmental Agriculture
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• v.23 no.4
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• pp.234-239
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• 2004

[ $NO_3$ ]-N and T-N removal rates of cattail wetland cells were compared with those of reed wetland cells. The examined cells were a part of a pond-wetland system composed of two ponds in series and six wetland cells in parallel. Each wetland cell was 25m in length and 6m in width. Cattails (Typha angustifolia) were transplanted into three cells and reeds Phragmites australis) into another three ones in June 2000. Water of Sinyang stream flowing into Kohung Estuarine lake located in the southern part of the Korean Peninsula was pumped into the primary pond, its effluent was discharged into the secondary pond Effluent from the secondary pond was funneled into each cell. Two cattail and reed cells were chosen for this research. Water quantity and quality of influnt and effluent were analyzed front May 2001 through October 2001. The volume of influent and effluent of the cells averaged about $20.0\;m^3/day$ and $19.3\;m^3/day$, respectively. Hydraulic retention time was approximately 1.5 days. Influent $NO_3$-N concentration for the four cells averaged 2.39 mg/L. Effluent $NO_3$-N concentration far the cattail and reed cells averaged 1.74 and 1.78 mg/L, respectively. Average $NO_3$-N retention rate for the cattail and reed cells by mass was 30 and 29%, respectively. Influent T-N concentration far the four cells averaged 4.13 mg/L. Effluent T-N concentration for the cattail and reed cells averaged 2.55 and 2.61 mgL respectively. Average T-N retention rate for the cattail and reed cells by mass was 39 and 38%, respectively. $NO_3$-N and T-N concentrations in effluent from the cattail cells were significantly low (p=0.04), compared with those from the reed cells. Cattail wetland cells were more efficient for $NO_3$-N and T-N abatement than reed ones.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.4
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• pp.363-368
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• 2007

Lithium-ion batteries providing high gravimetric energy density are rapidly replacing Ni-Cd and Ni-H2 in aerospace applications. The main advantage is the weight reduction of the battery system. Weight is a major concern in aerospace applications. Also, lithium-ion offer low thermal dissipation, high energy efficiency, and low cell cost. The Onboard battery module for KSLV-I(Korea Space Launch Vehicle) contains 80 Sony US18650 cells configured as 10 strings in parallel, with each string containing 8 series connected cells. This allows to meet voltage and capacity requirements specified for the mission. In this paper design description and specifications of lithium-ion battery developed are presented. Qualification test flow is also shown to make sure the performance in the predicted space environment. Electrical performance was simulated by dedicated program, and verified with electronic load. Lastly, the capacity was proven on real equipment load assembly.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.269-274
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• 2016

This paper proposes the development of a low frequency electronic hammer drive system that is used to prevent scaling or clogging in the hopper process. The electro-mechanical hammering driving method involves the generation of vibration and impact energy. The operation principles of the electromagnetic hammer were considered by parallel/series spring coefficient analysis and the amount of kinetic energy generated was calculated from the product of the equivalent spring constant, which is coupled with the E core and the gap of between the E core and I core. In addition, the Pulsation Driving algorithm was applied to the proposed electromagnetic hammer to obtain the maximizing kinetic energy. This algorithm was then implemented by a logical AND operation process and micro-controller (atmega128) built in functions with a timer interrupt and PWM generation function. The driving circuit of the electromagnetic hammer was designed using the H-bridge type IGBT circuit. The experimental test was performed by usefulness of the developed electromagnetic hammer systems with the acceleration measurement method. The experimental result showed that the proposed system has good kinetic energy generation performance and can be applied to the hopper process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.1051-1058
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• 2014

This paper presents a Electrical characteristics of the Memristor device using the PSPICE for circuit analysis. After making macro model of the Memristor device for circuit analysis, electric characteristics of the model such as time analysis, frequency and DC analysis according to the input voltage were performed by PSPICE simulation. Also, we made simple circuits of memristor series and parallel structure and analyzed the simulated SPICE results. Finally, we made a memristor-capacitor (M-C) circuit. charge and discharge characteristics were analyzed. In case of input pulse signal of 250 Hz, the Memristor-capacitor circuit showed delay time of 0.6ms, rising time of 0.58 ms and falling time of 1.6 ms.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.8
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• pp.1340-1346
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• 2016

Utilization of Distributed Generations (DGs) using Renewable Energy Sources (RESs) has been constantly increasing as they provide a lot of environmental, economic merits. In spite of these merits, some problems with respect to voltage profile, protection and its coordination system due to reverse power flow could happen. In order to analyze and solve the problems, accurate modeling of DG systems should be preceded as a fundamental research task. In this paper, we present a PhotoVoltaic (PV) generation system which consists of practical PV cells with series and parallel resistor and an inverter for interconnection with a main distribution system. The inverter is based on controllable current source which is capable of controlling power factors, active and reactive powers within a certain limit related to amount of PV generation. To verify performance of the model, a distribution system based on actual data is modeled by using ElectroMagnetic Transient Program (EMTP) software. Computer simulations according to various conditions are also performed and it is shown from simulation results that the model presented is very effective to study DG-related researches.

• Journal of the Korean Institute of Gas
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• v.24 no.4
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• pp.32-38
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• 2020

Based on the cases of fire and explosion accident in the chemical reactor, thr problems of preventive measures installed in the chemical reactor were analyzed. The chemical reactors produce a variety of chemicals and install rupture disk to relieve the pressure that rises sharply in the event of a runaway reaction. In order to maintain the function of the rupture disk, the emissions was allowed to be discharged into the atmosphere, resulting in fire and explosion accidents. As a way to improve this, safety instrumented system based on the safety integrity level(SIL3) was applied as a preventive measures for chemical reactor. Two emergency shur-off valves are installed in series on pipe dropping raw materials for chemical reactor so that the supply of raw materials can be cut off even if only one of the two emergency shut-off valves is operated during the runaway reaction. The automatic on/off valve is installed in parallel in the supply pipe of the reaction inhibitor so that the reaction inhibitor can be injected even if only one valve is opened at the time of the runaway reaction.