• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.175-177
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• 2006

Here we report an enhanced flexoelectric switching in a self-assembled system of smectic liquid crystal and some specific dopant. The assembled unit block seemed to have electric dipole and as a result induces large flexoelectric polarization due to its asymmetric shape and shows fast switching to the electric field. The unit blocks are oriented in a helical fashion in the cell with large gap (${\sim}5{\mu}m$) and shows selective reflection property. In the thin cell (${\sim}2{\mu}m$), the unit blocks are aligned homeotropically on the bare ITO substrate with no surface treatment and shows fast decaying time.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.125-125
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• 2010

The Hybrid Fault current limit combined the semiconductor switching components, for example IGBT, with mechanical fast switch reduced mechanical and thermal stress on electrical machines, for example circuit breaker, transformer, and so on, in the electric network. We had focused on reducing the voltage stress of the semiconductor switching components by the mechanical fast switch. As a result, we could dramatically reduce amount of semiconductor switching components only using parallel arrangement of them, not series.

• Journal of Power Electronics
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• 제11권4호
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• pp.520-526
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• 2011

This paper presents a balanced soft-chopping circuit and a modified PI controller for a high speed 4/2 Switched Reluctance Motor (SRM) with a 16 pulse per revolution encoder. The proposed balanced soft-chopping circuit can supply double the switching frequency in the fixed switching frequency of power devices to reduce current ripple. The modified PI controller uses maximum voltage, back-emf voltage and PI control modes to overcome the over-shoot current due to the time delay effect of current sensing. The maximum voltage mode can supply a fast excitation current with consideration of the hardware time delay. Then the back-emf voltage mode can suppress the current over-shoot with consideration of the feedback signal delay. Finally, the PI control mode can adjust the phase current to a desired value with a fast switching frequency due to the proposed balanced soft-chopping technology.

• Journal of Electrical Engineering and Technology
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• 제7권3호
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• pp.297-303
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• 2012

This paper presents the simulation results for the analysis of a lightning surge, switching transients and very fast transients within a thermal plant. The modeling of gas insulated substations (GIS) makes use of electrical equivalent circuits that are composed of lumped elements and distributed parameter lines. The system model also includes some generators, transformers, and low voltage circuits such as 24V DC rectifiers and control circuits. This paper shows the simulation results, via EMTP (Electro-Magnetic Transients Program), for three overvoltage types, such as transient overvoltages, switching transients, very fast transients and a lightning surge.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2017년도 전력전자학술대회
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• pp.188-189
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• 2017

There has been a growing demand for power semiconductor switches equipped with high-voltage blocking capability of kV range and fast-switching characteristics of ns range in various plasma application. This paper investigates the application of SiC MOSFETs in the particular plasma application which requires the blocking voltage of 4.5kV and the switching transient time of less than 100ns. In order to meet the required blocking voltage, the series connection of multiple SiC MOSFETs is adopted in this paper. Also, snubber capacitors are employed to equalize the voltage sharing among the series connected SiC MOSFETs. The simulation and experimental result successfully verifies the application of SiC MOSFETs and snubber capacitors in the plasma application requiring high-voltage and fast-switching load dynamics.

• 한국전기전자재료학회논문지
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• 제17권12호
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• pp.1264-1270
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• 2004

A fast switching thyristor with a superior trade-off property between the on-state voltage drop and the turn-off time could be fabricated by the proton irradiation method. After making symmetric thyristor dies with a voltage rating of 1,600 V from 350 $\mu$m thickness of 60 $\Omega$ㆍcm NTD-Si wafer and 200 $\mu$m width of n-base drift layer, the local carrier lifetime control by the proton irradiation was performed with help of the HI-13 tandem accelerator in China. The thyristor samples irradiated with 4.7 MeV proton beam showed a superior trade-off relationship of $V_{TM}$ = 1.55 V and $t_{q}$ = 15 $\mu$s attributed to a very narrow layer of short carrier lifetime(～1 $\mu$s) in the middle of its n-base drift region. To explain the small increase of $V_{TM}$ , we will introduce the effect of carrier compensation at the low carrier lifetime region by the diffusion current.ffusion current.t.

• Journal of Power Electronics
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• 제12권6호
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• pp.895-903
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• 2012

This paper presents a fast switching direct torque control (FS-DTC) using only a single DC-link current sensor. In FS-DTC, six new active voltage complex space vectors (CSVs) are synthesized by the conventional active voltage space vectors (SVs). The corresponding sectors are rotated in the anticlockwise direction by 30 degrees. A selection table is defined to select the CSVs. Based on the "Different Phase Mode", the output sequence of the selected CSV is optimized. Accordingly, a reconstruction method is proposed to acquire the phase currents. The core of the FS-DTC is that all of the three phase currents can be reliably reconstructed during every two sampling periods, which is the result of the fast switching between different phases. The errors between the reconstructed and actual currents are strictly limited in one sampling period. The FS-DTC has the advantages of the standard DTC scheme such as simple structure, quick torque response and robustness. As can be seen in the analysis, the FS-DTC can be thought of as an equivalent standard DTC scheme with 86.6% of the maximum speed, 173.2% of the torque ripple, and 115% of the response time of the torque. Based on a dSPACE DS1103 controller, the FS-DTC is implemented in an induction machine drive system. The results verify the effectiveness of the FS-DTC.

• 한국정보시스템학회지:정보시스템연구
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• 제23권2호
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• pp.109-137
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• 2014

As the fast development of information technology (IT), abundant attractive alternatives have showed up and challenged to the traditional information technology (IT). Cloud services, the hottest representative among these alternatives, has attracted the attention from all walks of life. Considering the diversity of cloud services, this study attempts to find out the important factors affected on individual's switching intention from incumbent IT to cloud services mainly based on two-factor theory (switching enablers and switching inhibitors) and explore the direct influences of these factors on individual's switching intention. According to our findings, individual's switching intention to cloud services is not only positively influenced by switching enablers but also negatively influenced by switching inhibitors. All the switching enablers in this study (perceived omnipresence, perceived collaboration support and perceived compatibility of cloud services) have positively significant influences on individual's switching intention as well as the switching inhibitors (usage habit of incumbent IT and perceived risk of cloud services) have negatively significant influences on individual's switching intention. It's noteworthy that satisfaction of incumbent IT has insignificant influence on individual's switching intention in this study. Moreover, as we expected, both social influence and personal innovativeness have significant influences on the generation of individual's switching intention.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
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• pp.253-256
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• 1996

In this paper, A new time-varying sliding surface design using eigenvalue locus is proposed to achieve fast and robust in a class of high-order uncertain dynamic system. A moving sliding surface(MSS) was proposed earlier for the second-order variable structure control systems(VSCS). This methodology led to fast and robust control responses of the second-order VSCS. However, the moving algorithm of the MSS was too complicated to be employed the high-order VSCS. To resolve this problem, we propose a new moving algorithm that switching surface moves such that the eigenvalues of equivalent system in the sliding mode have a predetermined locus. Using the proposed surface fast and robust behaviors are accomplished. The problem of chattering can be eliminated by using a boundary layer of switching surface. The efficiency of proposed algorithm is illustrated by an application to four-order workbench.

• Journal of Electrical Engineering and Technology
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• 제8권1호
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• pp.11-19
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• 2013

Very Fast Transients (VFT) originate mainly from disconnector switching operations in Gas Insulated Substations (GIS). In order to determine the rate-of-rise of Very Fast Transient Overvoltage (VFTO) in a 550 kV GIS, simulations are carried out using EMTP-RV. Each component of the GIS is modeled by distributed line model and lumped model based on equivalent circuits. The various switching conditions according to closing point-on-wave and trapped charge are simulated, and the results are analyzed. Also, the analysis of travelling wave using a lattice diagram is conducted to verify the simulation results.