• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.37.1-37.1
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• 2010

The multi-component olivine cathode material, $LiMn_{1/3}Fe_{1/3}Co_{1/3}PO_4$, was prepared via a novel coprecipitation method of the mixed transition metal oxalate, $Mn_{1/3}Fe_{1/3}Co_{1/3}(C_2O_4){\cdot}2H_2O$. The stoichiometric ratio and distribution of transition metals in the oxalate, therefore, in the olivine product, was affected sensitively by the environments in the coprecipitation process, while they are the important factors in determining the electrochemical property of electrode materials with multiple transition metals. The effect of the pH, atmosphere, temperature, and aging time was investigated thoroughly with respect to the atomic ratio of transition metals, phase purity, and morphology of the mixed transition metal oxalate. The electrochemical activity of each transition metal in the olivine synthesized through this method clearly was enhanced as indicated in the cyclic voltammetry (CV) and galvanostatic charge/discharge measurement. Three distinctive contributions from Mn, Fe, and Co redox couples were detected reversibly in multiple charge and discharge processes. The first discharge capacity at the C/5 rate was $140.5\;mAh\;g^{-1}$ with good cycle retention. The rate capability test showed that the high capacity still is retained even at the 4C and 6C rates with 102 and $81\;mAh\;g^{-1}$, respectively.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.4
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• pp.225-233
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• 2021

Conventional submarine propulsion batteries have mainly used lead acid batteries, which have proved relatively safe, but in recent years, research on mounting lithium-ion batteries to improve the underwater operation capability of submarines is underway in advanced countries such as Japan. Korea has world-class technology in the development of electric vehicles and lithium-ion batteries for energy storage, but fire safety accidents continue to occur in electric vehicles and energy storage lithium-ion batteries. In order to mount the lithium-ion battery in a submarine, it is necessary to check the safety as well as whether the performance is improved compared to the lead acid battery. Through the charge/discharge experiment of this lithium-ion battery module unit, it was possible to measure how much performance was improved compared to the lead acid battery. Safety tests were conducted on the lithium-ion battery module assuming that it was mounted on a submarine, and it was confirmed that safety was secured when applied to a submarine. Since many modules are mounted on actual submarines, it has been confirmed that it can be applied to submarine systems by simulating charge/discharge characteristics through Hardware-in-the Loop(HILS). Through the results of this study, the application of lithium-ion batteries to submarines is expected to significantly improve the sustainability of underwater operations.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4B
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• pp.375-381
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• 2008

In this research, a physics based grid-multi layer distributed flood runoff model was developed to analyze discharge for the Namgang Dam Watershed ($2,293km^2$) and applied for sensitivity analysis for estimation of parameters, mainly initial soil moisture condition and saturate infiltration coefficient, which have a strong influence on discharge. Capability of the model was evaluated using VER and QER from the results of rainfall-runoff analysis and showed enhanced results of 6% compared to parameters before calibration. As the result with the sensitivity analysis of parameters, the part of the most influence on the runoff was the infiltration coefficient and ratio of layer partition. The total discharge and peak time showed comparatively precise runoff results without the initial calibration of the parameters.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.6
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• pp.474-481
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• 2011

The discharge coefficient and spatial velocity distribution were clarified by carrying out a physical experiment to assess the performance of sluice for tidal power generation. The physical experiment was performed by manufacturing 10 sluce models whose scale is 1/70 of the prototype and installing it in the planar open channel, which has apron sections in front of and behind the sluice models. In particular, it was attempted to reasonably determine the locations and method of measuring water levels that may affect estimation of the discharge coefficient. Based on the experimental results for various conditions of discharges and tidal levels, the discharge coefficient of the sluice in the experiment was estimated as 1.3 to 1.4. Meanwhile, it was found that velocities were 2~3% faster at the sluices near the central region whereas 4~5% slower at the sluices on both sides, in comparison to the average value of the mean velocities of the ten sluices.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.6
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• pp.50-55
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• 2011

The fluid power products are widely used in current industrial area such as automation of products and equipment assembly, high-tech machine tool, aircraft, train, and etc. As the development of industry is in progress, the development of the fluid power products is demanding and it is required in every industrial area. This research proposed a pneumatic system to evaluate displacement accuracy of the pneumatic actuator without external load and to analyze capability of integration of the valve system. The pneumatic system consisted of a combination of pneumatic actuator, four two-port valves, two three-port valves, two pressure valve, a check valve, two proximity sensors, and a program logic controller (PLC). The position controller is based on the PLC connected with the proximity sensors. The maximum air pressure applied for tests was $49.05N/cm^2$ and the displacement accuracy of a stroke was measured using a dial gauge. The supply- and discharge-side of air pressure and the length of the stroke of the pneumatic cylinder were varied The test of the position control of the pneumatic cylinder was carried out 50 times at each supply- and discharge-side air pressure of 24.53/34.34, 29.43/39.24, 34.34/44.15, and $39.24/49.05N/cm^2$ and replicated three times. The accuracy of the displacement of the pneumatic cylinder stroke increased as the supply- and discharge-side of air pressure increased with the stroke length of 133mm. Also the displacement accuracy increased as the stroke length increased with the fixed supply- and discharge-side of air pressure of the pneumatic cylinder as 34.34 and $44.15N/cm^2$, respectively. The most accurate displacement of the pneumatic cylinder was obtained at the supplyand discharge-side of air pressure of 39.24 and $49.05N/cm^2$, respectively, and strokes of 170 and 190mm.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.10
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• pp.1810-1814
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• 2006

In this paper, the brightmess from inside gas pressure, applied voltages, and operation frequency conditions was measured and the discharge characteristics in FFL(Flat Fluorescent Lamp) also were measured and discussed. The brightness and lifetime after vacuum exhaust ($350^{\circ}C$ and 1 hour) ate remarkably developed. When the gas pressure of lamp-inside is high, the brightness is also increased automatically. But for the stabilization of operation and driving voltage, the highest values of brightness at about 1000[V], 300[Torr] and 64(kHz) are measured and the results are shown as the optimized driving conditions for FFL.

• Journal of Electrical Engineering and Technology
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• v.10 no.5
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• pp.1983-1988
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• 2015

This paper proposes the enhanced application of superconducting magnetic energy storage (SMES) for the effective compensation of power fluctuations based on the interleaving technique. With increases in demand for renewable energy based photovoltaic (PV) generation system, the output power fluctuations from PV generation system due to sudden changes in environmental conditions can cause serious problems such as grid voltage and frequency variations. To solve this problem, the SMES system is applied with its superior characteristics with respect to high power density, fast response for charge and discharge operations, system efficiency, etc. In particular, the compensation capability is effectively improved by the proposed interleaving technique based on its parallel structure. The dynamic performance of the system designed using the proposed method is evaluated with several case studies through time-domain simulations.

• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.37-39
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• 2008

In this paper, a three-port bidirectional modular circuit applied in charging and discharging equalization for lithium-ion battery strings is proposed. This circuit consists of four MOSFETs and one transformer which provide a simple structure to be easily modularized. Compared to conventional individual cell equalization schemes, it utilizes the transformer as the energy transfer element, allowing direct transfer of energy between arbitrary two cells of three-cell battery module, thus improving the equalization efficiency significantly by using much less number of equalizers for long battery strings. Simulation results are presented to validate the circuit operation and confirm its capability to equalize the three-cell battery module.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.10
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• pp.530-535
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• 2001

Resonant-type electronic ballast for a metal halide discharge(MHD) lamp is proposed and implemented for 400W MHD lamp. HID lamps have good color rendition, long life and good focusing capability but they have flickers by acoustic resonance when driven at high frequency. A new control method is employed to remove acoustic resonance related instability in HID lamp. By using the amplitude modulation, a spread spectrum effect is employed on the ballast. The control loop of resonant inverter is analyzed and a current is designed. The ballast consists of a power factor controller, an half-bridge resonant inverter, a simple ignitor and an integrator with OP-amps. The experimental results show the good performance as PF 0.93, ballast loss 22W at output 400W and the conducted EMI level is below 60dBuV.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.1
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• pp.84-92
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• 2001

In this papers, we proposed the new method in order to diagnosis aging state of transformers. For wavelet transform, Daubechies filter is used, we can obtain wavelet coefficients which is used to extract feature of statistical parameters (maximum value, average value, dispersion skewness, kurtosis) about each acoustic emission signal. Also, these coefficients are used to identify normal and fault signal of internal partial discharge in transformer. As improved method for classification use neural network. Extracted statistical parameters are input into an back-propagation neural network. The number of neurons of hidden layer are obtained through Result of Cross-Validation. The network, after training, can decide whether the test signal is early aging state, alst aging state or normal state. In quantity analysis, capability of proposed method is superior to compared that of classical method.