• Journal of Power Electronics
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• v.16 no.5
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• pp.1894-1903
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• 2016

In general, electrolytic capacitors are used to reduce power pulsations on PV-panels. However, this can reduce the reliability of the PV AC-module system, because electrolytic capacitors have a shorter lifetime than PV-panels. In addition, PV-panels generate irregular power and inject it into the grid because the output power of a PV-panel depends on the surrounding conditions such as irradiation and temperature. To solve these problems, a grid-connected photovoltaic (PV) AC-module with active power decoupling and energy storage is proposed. A parallel bi-directional converter is connected to the AC module to reduce the output power pulsations of PV-panels. Thus, the electrolytic capacitor can be replaced with a film capacitor. In addition, the irregular output power due to the surrounding conditions can be regulated by using a parallel energy storage circuit. To maintain the discontinuous conduction mode at low irradiation, the frequency control method is adopted. The design method of the proposed converter and the operation principles are introduced. An experimental prototype rated at 125W was built to verify the performance of the proposed converter.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.15-16
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• 2010

This paper is study on a high efficiency DC-DC converter of discontinuous conduction mode (DCM) added electric isolation. The converters of high efficiency are generally made that the power losses of the used semiconductor switching devices is minimized. To achieve high efficiency system, the proposed converter is constructed by using a quasi resonant circuit. The control switches using in the converter are operated with soft switching by quasi resonant method. The control switches are operated without increasing their voltage and current stresses by the soft switching technology. The result is that the switching loss is very low and the efficiency of the system is high. The proposed converter is also added electric isolation which is used a pulse transformer. When the power conversion system is required electric isolation, the proposed converter is adopted with the converter system development of high efficiency. The soft switching operation and the system efficiency of the proposed converter are verified by digital simulation and experimental results.

• The KIPS Transactions:PartB
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• v.10B no.6
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• pp.639-646
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• 2003

This paper proposes a neural network model for extracting optical illusions produced by a sequence of discontinuous dot stimuli. The proposed model is based on visual cell's characters founded by visual information processing path. This study approaches on the basis of physiological observation of the perceptual phenomena that some simple ways of discrete dots are perceived as a continuous virtual contour rather than as separate dots. This paper presents the implementation of the optical illusions from discrete dot stimuli that are composed of virtual polygons from 6 to 10 dots. This experimental data are similar to those of Smith & Vos's physiological experiments. The proposed model shows that it can extract continuous illusion contours from discrete dot stimuli successfully.

• Journal of Power Electronics
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• v.13 no.4
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• pp.636-646
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• 2013

A single-phase tapped-inductor boost converter has been proposed previously. However, detailed characterization and performance analysis were not conducted. This paper presents a detailed characterization, performance analysis, and design expressions of a single-phase tapped-coupled-inductor boost converter. Expressions are derived for average and RMS input current as well as for RMS input and output capacitor current ripple. A systematic approach for sizing the tapped-coupled inductor, active switch, and output diode is presented; such approach has not been reported in related literature. This study reveals that sizing of the inductor has to be based on current ripple requirement, turns ratio, and load. Conditions that produce discontinuous inductor current are also discussed. Analysis of a non-ideal converter operating in continuous conduction mode is also conducted. The expression for the voltage ratio considering the coupling coefficient is derived. The suitability of the converter for high-voltage step-up applications is evaluated. Factors that affect the voltage boost ratio are also identified. The effects of duty ratio and load variation on the performance of the converter are also investigated. The theoretically derived characteristics are validated through simulations. Experimental results obtained at a low power level are included to validate the analytical and simulation results. A good agreement is observed among the analytical, simulation, and experimental results.

• Journal of Power Electronics
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• v.18 no.3
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• pp.662-671
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• 2018

This paper presents a new structure for a step up dc-dc converter, which has several advantageous features. Firstly, the input dc source and the clamped capacitor are connected in series to transfer energy to the load through dual voltage multiplier cells. Therefore, the proposed converter can produce a very high voltage and a high conversion efficiency. Secondly, a double voltage clamped circuit is introduced to the primary side of the coupled inductor. The energy of the leakage inductance of the coupled inductor is recycled and the inrush current problem of the clamped circuits can be shared equally by two synchronous clamped capacitors. Therefore, the voltage spike of the switch tube is solved and the current stress of the diode is reduced. Thirdly, dual voltage multiplier cells can absorb the leakage inductance energy of the secondary side of the coupled inductor to obtain a higher efficiency. Fourthly, the active switch turns on at almost zero current and the reverse-recovery problem of the diodes is alleviated due to the leakage inductance, which further improves the conversion efficiency. The operating principles and a steady-state analysis of the continuous, discontinuous and boundary conduction modes are discussed in detail. Finally, the validity of this topology is confirmed by experimental results.

• Proceedings of the KIEE Conference
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• 2002.04a
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• pp.133-138
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• 2002

The developments of the solar and the wind power energy are necessary since the future alternative energies that have no pollution and no limitation are restricted. Currently power generation system of MW scale has been developed, but it still has a few faults with the weather condition. In order to solve these existing problems, combined generation system of photovoltaic(400W) and wind power generation system(400W) was suggested. It combines wind power and solar energy to have the supporting effect from each other. However, since even combined generation system cannot always generate stable output with ever-changing weather condition, power compensation device that uses elastic energy of spiral spring to combined generation system was also added for the present study. In an experiment, when output of system gets lower than 12V(charging voltage), power was continuously supplied to load through the inverter by charging energy obtained from generating rotary energy of spiral spring operates in small scale generator.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.7
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• pp.1-11
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• 2006

Through the analysis of conventional TVD limiters, a new multi-dimensional limiting function is derived for an oscillation control in multi-dimensional flows. Then, Multi-dimensional Limiting Process (MLP) is developed with the multi-dimensional limiting function. The major advantage of MLP is to prevent oscillations across a multi-dimensional discontinuity, and it is readily compatible with more than 3rd order spatial interpolation. Moreover, MLP shows a good convergence characteristic in a steady problem and it is very simple to be implemented. Through numerical test cases, it is verified that MLP substantially improves accuracy, efficiency and robustness both in continuous and discontinuous flows.

• Journal of Environmental Science International
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• v.28 no.12
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• pp.1123-1131
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• 2019

In this study, we investigated the spatial range, distribution pattern, temporal appearance, sex ratio, seasonal pattern, and size of the population of Leptalina unicolor locally inhabiting the wetland protection area in the Jaeyaksan Mountain. We found that the butterfly was distributed across four areas at 750 m above sea level and in an area of 96,000 ㎡. in the southeastern slope of the mountain. The discontinuous distribution of the butterflies in the meadow. According to our survey conducted from 2012 to 2014, L. unicolor occurred in May (spring) and July (summer) each year, with the male population more than three times higher than that of the female population. The population size estimated using the mark and recapture method on the back of the hind wing in the two years was as follows: 877±502 and 1243±800 individuals in the spring and summer of 2012, respectively, and 783±429 and 506±365 individuals in the spring and summer of 2014, respectively, suggesting no specific seasonal pattern. The findings of this study are expected to be useful for the conservation of the populations and habitats of L. unicolor, which are currently distributed locally due to a decrease in population size.

• Korea-Australia Rheology Journal
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• v.21 no.3
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• pp.193-200
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• 2009

We present a direct simulation technique for two-dimensional mold-filling simulations of fluids filled with a large number of circular disk-like rigid particles. It is a direct simulation in that the hydrodynamic interaction between particles and fluid is fully considered. We employ a pseudo-concentration method for the evolution of the flow front and the DLM (distributed Lagrangian multipliers)-like fictitious domain method for the implicit treatment of the hydrodynamic interaction. Both methods allow the use of a fixed regular discretization during the entire computation. The discontinuous Galerkin method has been used to solve the concentration evolution equation and the rigid-ring description has been introduced for freely suspended particles. A buffer zone, the gate region of a finite area subject to the uniform velocity profile, has been introduced to put discrete particles into the computational domain avoiding any artificial discontinuity. From example problems of 450 particles, we investigated the particle motion and effects of particles on the flow for both Newtonian and shear-thinning fluid media. We report the prolonged particle movement toward the wall in case of a shear-thinning fluid, which has been interpreted with the shear rate distribution.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.4
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• pp.127-133
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• 2008

As the application of the MEMS parts increases, the structural safety of MEMS appears importantly. A lot of MEMS parts are made by a multi-grain silicon wafer, which is an orthotropic material. Moreover directions of the materials on each grain are distributed randomly. The stress analysis for the multi-grain is important factor in order to apply the MEMS parts to industrial applications. The finite element method (FEM) is commonly used by a stress analysis method but the boundary element method (BEM) is known as the result of the BEM is more accurate than that of the FEM since the fundamental solution are used. In this study, we derived the boundary integration equation for the orthotropic material by applying fundamental solutions with complex variables. The multi-region analysis procedure for the BEM and the multi-grain generation procedure by a random process technique are developed in order to apply the analysis of the multi-grain orthotropic material. The discontinuous element is used in order to remove the comer problem in the BEM. The results of the present method are compared with those of the finite element method in order to verify the present procedure.