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Lim Y.-C.,Chonnam National University | Wi S.-O.,Korea Astronomy and Space Science Institute | Kim J.-N.,Celrun Company | Jung Y.-G.,Sehan University
IEEE Transactions on Power Electronics | Year: 2010

This paper describes a pseudorandom carrier modulation scheme and its harmonic spectra spread effect. The pseudorandom carrier of the proposed scheme are produced through the random synthesis of the two triangular carriers, each of the same fixed frequency, but of opposite phase. The random selection of the two triangular carriers is decided by ''0'' or ''1'' states of the pseudorandom binary sequence (PRBS) random bits. Multiplexer which are used as random selector of the PRBS random bits, produces the resultant pseudorandom frequency carrier waveform. In order to verify the validity of the proposed method, the simulations and experiments were conducted and tested with a single-phase low-power H-bridge multilevel inverter. An EXAR XR2207 is used as a triangular carrier generator with fixed frequency, also an XR2206 is used for generation of single-phase sinusoidal wave. The PRBS random bits generator is implemented, using a shift register and an EXCLUSIVE OR gate. The experimental results show that the harmonics spectra of voltage and current are dispersed over a wide-band area by using the proposed scheme. © 2006 IEEE.

Nguyen M.-K.,Chonnam National University | Jung Y.-G.,Sehan University | Lim Y.-C.,Chonnam National University | Kim Y.-M.,Celrun Inc. | Kim Y.-M.,Trigem Computer Inc.
IEEE Transactions on Power Electronics | Year: 2010

This paper proposes a new type of converter called a single-phase Z-source buckboost matrix converter. The converter can buck and boost with step-changed frequency, and both the frequency and the voltage can be stepped up or stepped down. In addition, the converter employs a safe-commutation strategy to conduct along a continuous current path, which results in the elimination of voltage spikes on switches without the need for a snubber circuit. The operating principles of the proposed single-phase Z-source buckboost matrix converter are described, and a circuit analysis is provided. To verify the performance of the proposed converter, a laboratory prototype was constructed with a voltage of 40 Vrms/60 Hz and a passive RL load. The simulation and the experimental results verified that the converter can produce an output voltage with three different frequencies 120, 60, and 30 Hz, and that the amplitude of the output voltage can be bucked and boosted. © 2010 IEEE.

Nguyen M.-K.,Chonnam National University | Jung Y.-G.,Sehan University | Lim Y.-C.,Chonnam National University
IEEE Transactions on Power Electronics | Year: 2010

This paper deals with a new family of single-phase ac-ac converters called single-phase quasi-Z-source ac-ac converters. The proposed converter inherits all the advantages of the traditional single-phase Z-source ac-ac converter, which can realize buck-boost, reversing, or maintaining the phase angle. In addition, the proposed converter has the unique features that the input voltage and output voltage share the same ground and the operation is in the continuous current mode. The operating principles of the proposed converter are described, and a circuit analysis is provided. In order to verify the performance of the proposed converter, a laboratory prototype was constructed with a voltage of 84 Vrms/60 Hz. The simulation and experimental results verified that the converter has a lower input current total harmonic distortion and higher input power factor in comparison with the conventional single-phase Z-source ac-ac converter. © 2010 IEEE.

Jung H.-R.,Chonnam National University | Cho S.J.,Chonnam National University | Kim K.N.,Sehan University | Lee W.-J.,Chonnam National University
Electrochimica Acta | Year: 2011

The CuxO (x = 1, 2)-embedded carbon nanofibers (Cu xO/CNF) were prepared by electrospinning of the composite solutions of Cu(II) acetate, PAN (polyacrylonitrile) and PVP (polyvinylpyrrolidone), and subsequent stabilization and carbonization. The structure of Cu2O/CNF is largely dependent on the carbonization temperature. The Cu xO/CNF-700 has the disordered CuO structure, while the Cu xO/CNF-800 has the intermediate structure between the disordered CuO and Cu2O. The structural change in the CNF prepared by electrospinning and optimum thermal treatment leads to excellent electrochemical properties. The CNF plays an important role as buffering agent to prevent CuxO particles from agglomerating. Besides, the aligned CNF with high electrical conductivity leads to the occurrence of Cu nano-particles in the discharging process, and it serves to convert Li2O into Li in the charging process. Both CuxO/CNF-700 and CuxO/CNF-800 exhibit high specific discharge capacity, exceptional cycle retention, and excellent reversible capacity even in initial cycle, while Cu xO/CNF-900 shows bad electrochemical performance. © 2011 Elsevier Ltd. All rights reserved.

Jung Y.-G.,Sehan University
Journal of Electrical Engineering and Technology | Year: 2013

The conventional graphical representation of the instantaneous compensation power flow for single-phase active power filters(APFs) simply represents the active power flow and the reactive power flow which flowing between the power source and the active filter/the load. But, this method does not provide the information about the rectification mode and the compensation mode of APFs, especially, the loss for each mode was not considered at all. This is very important to understand the compensation operation characteristics of APFs. Therefore, this paper proposes the graphical representation of the instantaneous compensation power flow for single-phase APFs considering the instantaneous rectification mode and the instantaneous inversion mode. Three cases are verified in this paper - without compensation, with compensation of the active power 'p' and the fundamental reactive power 'q', and with compensation of only the distorted power 'h'. To ensure the validity of the proposed approach, PSIM simulation is achieved. As a result, we could confirm that the proposed approach was easy to explain the instantaneous compensation power flow considering the instantaneous rectification mode and the instantaneous inversion mode of APFs, also, Total Harmonic Distortion(THD)/Power Factor (P.F) and Fast Fourier Transform(FFT) analysis were compared for each case.

Lee J.-Y.,Sehan University
2016 International Conference on Platform Technology and Service, PlatCon 2016 - Proceedings | Year: 2016

The purpose of this study is to investigate the general effect of dictogloss, which is an English teaching approach in Korean EFL. Fifty seven research cases from twenty two studies were used in the meta-analysis. Each study was classified in terms of research target participants (elementary, middle, and high school students), treatment period, and dependent variables. Dependent variables were divided into two categories; one is linguistic competence such as listening, reading, speaking, writing, grammar, and vocabulary, and the other is affective domain including interest and confidence. The research results using a meta-analysis suggest that there is a positive effect (g=.511) in the use of dictogloss. © 2016 IEEE.

The transit motion and the rotating motion have highly different effects in a technical systems and have almost nonlinear system behaviors. For the descriptions of their dynamical causes and effects on system, the physical information, which is concerned as a nonlinear mathematic model, has been used. But the corresponding equations are generally not easy to solve in complete form or their solutions are so complicated to see through the coherence. A common way to settle such a problem is to linearize system exactly in a state space or on a operating points with Taylor's series approximately. An advanced method to an approximation is a bilinear system that offers global separations principle. In this paper, an extended application of this theory is given in a modeling and control on the electro hydrostatic cylinder driver with both the transit and rotating motions for the keel system that mostly have not only advantage of high performance, small volume of building and weight but also high nonlinear behavior. © (2014) Trans Tech Publications, Switzerland.

Park J.-W.,Sehan University
Advanced Studies in Theoretical Physics | Year: 2014

In this paper, we defined a new q-extension of Bernoulli polynomials with weight by generating function, and investigate several properties of those polynomials. These q-Bernoulli polynomials are useful to study various identities of Carlitz’s qBernoulli numbers. © 2014 Jin-Woo Park.

Kim T.-H.,Sehan University | Sung A.-Y.,Sehan University
Journal of the Korean Chemical Society | Year: 2010

This study used 3-vinylanisole and 4-vinylanisole with the cross-linker EGDMA (ethylene glycol dimethacrylate), HEMA (2-hydroxyethyl methacrylate), MMA (methyl methacrylate), NVP (N-vinyl-2-pyrrolidone) and the initiator AIBN (azobisisobutyronitrile) for copolymerization. Measurement of the physical characteristics of the copolymerized material showed that the refractive index is 1.4496-1.4894, water content 22.93-35.50%, visible transmittance 88.8-90.8%. Also, measurements showed that the refractive index increased while the water content decreased as the ratio of 3-vinylanisole and 4-vinylanisole increased. And in cases of copolymer with 3-vinylanisole, 4-vinylanisole (added 15%) the results showed transmittance of 52.8-82.2%, 13.2-26.2% respectively for UV-A and UV-B showing that they have UV-blocking effects. Based on the results of this study, the produced copolymer can be estimated to be suitable for use as ophthalmic lens material for high refractive index and UV-blocking effects.

Recently, electrochemical-mechanical polishing (ECMP) has been suggested as an alternative to the conventional chemical-mechanical polishing (CMP) process. In ECMP process, copper (Cu) ions are electrochemically dissolved by applying an anodic potential to the Cu surface in an electrolyte. In this paper, the voltage-activated electrochemical reactions of Cu for ECMP application were investigated with different concentration of HNO3 electrolyte. The electrochemical characteristics of Cu such as active, passive, transient and trans-passive state were evaluated from its current-voltage (I-V) curve obtained by linear sweep voltammetry (LSV) and cyclic voltammetry (CV) method. The proposed mechanism and analyses were a good methodology in finding suitable electrochemical process parameter for ECMP application. © 2010 Elsevier B.V. All rights reserved.

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