• Journal of Power Electronics
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• v.14 no.5
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• pp.874-881
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• 2014

This study presents a single-phase power factor correction AC-DC converter that operates in discontinuous conduction mode. This converter uses the pulse-width modulation technique to achieve almost unity power factor and low total harmonic distortion of input current for universal input voltage $90V_{rms}$ to $264V_{rms}$) applications. The converter has a simple structure and electrical isolation. The magnetizing-inductor energy of the transformer can be recycled to the output without an additional third winding. The steady-state analysis of voltage gain and boundary operating conditions are discussed in detail. Finally, experimental results are shown to verify the performance of the proposed converter.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.1
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• pp.21-26
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• 2012

In recent years, DC distribution systems are becoming hot issue due to the increase in digital loads and DC generation systems according to the expansion of renewable energy technologies. However, removing the fault current in DC grids is comparably difficult since the current in DC grids has no zero-crossing point like in AC grids. Thus, developing dedicated DC circuit breakers for DC grids is necessary to get safety for people and electrical facilities. This paper proposes magnet arc extinguishing method to develop a 300[$V_{DC}$]/10[A] DC circuit breaker. The performance of the proposed DC circuit breaker was verified by an experimental circuit breaker test system built in this research.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.7
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• pp.1193-1205
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• 1994

This paper presents a fuzzy system that adaptively classifies subimages to four classes according to image activity distribution. In adaptive transform image coding, subimage classification improves the compression performance by assigning different bit maps to different classes. A conventional classification method sorts subimages by their AC energy and divides them to classes with equal number of subimages. The fuzzy system provides more flexible classification to natural images with various distribution of image details than does the conventional method. Clustering of training data in the input-output product space generated the fuzzy rules for subimage classification. The fuzzy system of small number of fuzzy rules successfully classified subimages to improve the compression performance of the transform image coding without sorting of AC energies.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1551-1553
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• 2000

Superconducting power cable is one of the most promising energy application of high-$T_c$ superconductors (HTS). A prototype HTS cable have been constructed multi-layer cable using Bi-2223 tape and tested. The result shows that the total transport current of HTS cable in $LN_2$ was 475[A], and transport current passed through almost the outer layer (2-layer). Also, AC transport losses in outer layer of HTS cable was proportion to $I^2$ and higher than losses of inner layer. As magnetic distribution were concentrated on outer layer.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2260-2264
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• 2012

The kinetics and mechanism of the pyridinolysis ($XC_5H_4N$) of dimethyl isothiocyanophosphate are investigated in acetonitrile at $55.0^{\circ}C$. The Hammett and Br$\ddot{o}$nsted plots for substituent X variations in the nucleophiles exhibit two discrete slopes with a break region between X = 3-Ac and 4-Ac. These are interpreted to indicate a mechanistic change at the break region from a concerted to a stepwise mechanism with a rate-limiting expulsion of the isothiocyanate leaving group from the intermediate. The relatively large ${\beta}x$ values imply much greater fraction of frontside nucleophilic attack TSf than that of backside attack TSb. The steric effects of the two ligands play an important role to determine the pyridinolysis rates of isothiocyanophosphates.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.73-77
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• 2015

Offshore wind farms extend a distance from an onshore grid to increase their generating power, but long distance and high power transmissions raise a lot of cost challenges. LFAC (Low Frequency AC) transmission is a new promising technology in high power and low cost power transmission fields against HVDC (High Voltage DC) and HVAC (High Voltage AC) transmissions. This paper presents an economic comparison of LFAC and HVDC transmissions for large offshore wind farms. The economic assessments of two different transmission technologies are analyzed and compared in terms of wind farm capacities (600 MW and 900 MW) and distances (from 25 km to 100 km) from the onshore grid. Based on this comparison, the economic feasibility of LFAC is verified as a most economical solution for remote offshore wind farms.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.7
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• pp.630-635
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• 2000

Superconducting power cable is one of the most promising energy application of high-T$\sub$2/ superconductor(HTS). Thus we investigated previously the electrical and mechanical characteristics on Bi-2223 Ag sheathed tape. And a prototype HTS cable have been designed constructed and tested. In case of 19-filament type transport losses agree with the results of norris theory(strip). The critical current of HTS cable(1, 19-filament) in LN$_2$was 116[A], 240[A] and degradation coefficient(k) was 0.71, 0.73 respectively. In case of 19-filament cable critical current was decreased because of mechanical strain at pitch. And AC loss of HTS cable(19-filament) was 0.7 [W/m] in 240[A] loading

• Journal of Power Electronics
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• v.16 no.1
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• pp.268-276
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• 2016

A hybrid sinusoidal-pulse current (HSPC) charging method for the Li-ion batteries in electric vehicle applications is proposed in this paper. The HSPC charging method is based on the Li-ion battery ac-impedance spectrum analysis, while taking into account the high power requirement and system integration. The proposed HSPC method overcomes the power limitation in the sinusoidal ripple current (SRC) charging method. The charger shares the power devices in the motor inverter for hardware cost saving. Phase shifting in multiple pulse currents is employed to generate a high frequency multilevel charging current. Simulation and experimental results show that the proposed HSPC method improves the charger efficiency related to the hardware and the battery energy transfer efficiency.

• Proceedings of the KIEE Conference
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• 1993.07a
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• pp.137-139
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• 1993

This paper details methods used to verify the adquacy of a dc traction power supply for design in Seoul matropolitain subway Line-6 system. Examples of the approach are given for a major subway presently under construction. The performance of trains operating at maximum system design capacity is modelled using a train simulation program. Using a dc network analyser program, the maximum train operating timetable, and a model of the ac and dc electrical suppy system, the electrical performance of the entire system can be modelled over a 24-hour period. The results of this analysis are used to determime: train voltage at a level sufficient to ensure train schedules: adequacy of traction transformers, rectifier, and switchgear ratings; sizes of the overhead contact systern conductors, and ac and de feeder cables: and power and energy demands at the utility company's supply points for inital and final timetable operations.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.90-93
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• 2001

This paper suggests the circuit topology to transfer AC power using a detachable transformer The circuit topology for AC output load through the magnetic coupling and its principle of operation are described. It can decrease the size of detachable transformer by employing the high-frequency magnetic coupling. It is shown in this paper that the efficiency of noncontact energy transfer system can be improved by applying both the full bridge converter with PFC function to the 1st side of its and the series resonance to the 2nd side to minimize the effect of the leakage inductance.