• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.205-205
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• 2012

Korea Superconducting Tokamak Advanced Research (KSTAR) 장치는 국내 유일의 초전도 자석을 이용한 핵융합 연구 장치로서 초고온의 플라즈마를 생성하여 차세대 에너지원인 핵융합 에너지를 획득하는 것을 목표로 두고 있다. 플라즈마를 생성부터 유지하기 위해서는 수소 동위원소를 토카막 내부로 공급해 주어야 하는데 이러한 수소동위원소를 "연료"라 부르며, 이 연료를 토카막 내부로 공급해 주는 시스템을 연료주입 시스템(Fueling System)이라고 한다. KSTAR에서는 토카막 내부로 고속의 연료 주입이 필요하고 정밀한 양의 연료를 공급하는 밸브를 사용하여야 하며, 이러한 밸브를 제어 할 수 있는 제어기를 필요로 한다. 위의 사항에 적합한 피에조 밸브(Piezoelectric Valve)는 2 msec 이내의 개폐시간과 500 Torr ${\ell}$/s 이상의 유량을 흘려줄 수 있는 피에조 밸브로 압전소자에 가해지는 전압(0~250 V)에 따라 변위의 양에 비례하여 연료가 진공용기 내로 유입된다. 압전소자의 변위는 최대 140 ${\mu}m$로 최적화되어 있어야 하며, 정전용량(Capacitance)는 30~40 nF이어야 한다. 또한 소자에 힘(Force)를 가해 최대 7 N으로 136 ${\mu}m$의 변위를 가진 소자를 사용해야 한다. 피에조 밸브의 특성으로는 아날로그 신호로 작동이 되어야 하며, 유량신호를 피드백하여 밸브의 구동 전압을 정밀하게 제어 되어야 한다. 피드백 제어를 위해 압력센서는 XCS-190 Series를 사용하여 낮은 유량에서도 민감하게 반응하도록 제작하였으며, 고전압이 유기 되었을 때 제어기를 보호하기 위한 정션박스를 설치하였다. 밸브 제어기는 피에조 밸브의 개방 속도를 높이기 위해 밸브 구동 전압을 순간적으로 높이는 POP 전압을 생성하는 기능과 유량 신호를 피드백해서 밸브 구동 전압을 정밀 제어 하는 기능을 가지고 있다. 제어장치는 아날로그 및 디지털 제어회로의 전원용 +15 V DC와 밸브 구동용 +250 V DC 출력용의 전원 공급 장치(Power supply unit), 펄스 및 트리거 신호를 생성하는 Master Programmer unit), Pop 전압과 피드백의 중요한 기능을 수행하는 Valve controller unit로 제작 되었다. 피에조 밸브와 제어기는 상호 작용하여 동작을 원활히 할 수 있도록 특성 실험을 진행하여야 하며, 진공상태에서 Lack의 유무를 확인하여야 한다. 현재 개발 제작된 밸브의 진공누설시험 및 특성실험을 진행하고 있으며, KSTAR 5차 캠페인에 적용할 계획이다.

• Journal of IKEEE
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• v.13 no.4
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• pp.82-88
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• 2009

This paper is analyzed for a step up-down DC/DC chopper of high efficiency added electric isolation. The converters of high efficiency are generally made that the power loss of the used semiconductor switching devices is minimized. To achieve high efficiency system, the proposed chopper is constructed by using a partial resonant circuit. The control switches using in the chopper are operated with soft switching by partial 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 chopper is high. The proposed chopper is also added electric isolation which is used a pulse transformer. When the power conversion system is required electric isolation, the proposed chopper is adopted with the converter system development of high efficiency. The soft switching operation and the system efficiency of the proposed chopper are verified by digital simulation and experimental results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.8
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• pp.911-918
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• 2010

With limitation of frequency bandwidth, the range accuracy of typical radars is limited. In this paper, for short distance measurements, the use of an AM(Amplitude Modulated) radar which provides improved range accuracy is proposed. The AM radar signal consists of a carrier frequency signal and double-sideband components. The fabricated AM radar operates with +10 dBm output power and 35 dB receiver gain at 24.128 GHz center frequency with 20 MHz bandwidth, and the range accuracy is measured as ${\pm}15\;cm$.

• Journal of Sensor Science and Technology
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• v.5 no.2
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• pp.47-54
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• 1996

This paper deals with the electric field sensor and automatic measuring system of the time-varying space electric field produced by lightning discharges. The theoretical principle and the design rule of the measuring devices are investigated, and the semisphere-type electric field sensor and the signal process system are fabricated. From the calibration experiments, the frequency bandwidth of the measuring system ranges from 200 [Hz] to 1.56 [MHz] and the sensitivity is 0.96 [m V/V/m] as the amplification gain is 10. In addition, the electric field waveforms produced by lightning discharges are observed by the proposed electric field measuring system from June to August in 1995. The data is sampled with the time interval of 200 [ns] and is automatically recorded by transient signal analyzer(Necolet Pro 30), the resolution of which is 12 bit. And it is registered at personal computer. The electric field waveforms produced by intracloud discharge tend to be bipolar, with two or three narrow and fast rising pulses superimposed on the initial half-cycle.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.2
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• pp.273-280
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• 1999

This paper presents the design and implementation of circuit analyzer system for the convenient troubleshooting and diagnosis of the electronics appliance using the curve tracer technology of analog signature analysis. The circuit analyzer provides advanced troubleshooting capabilities to simplify testing newer technology components such as CMOS and MOS circuits, its built-in pulse generator lets thoroughly troubleshoot gate-fired devices such as SCRs, TRIACs and optocouplers. The circuit analyzer while the power to the circuitry testing is turned of, so that avoid an accidental short that could cause further damage, its allow to analyze the impedance state of a solid-state component, which makes it perfect for finding leakage or substrate damage that has brought a system or PCB down prematurely. Because it can compare suspect components to known-good equivalents, it's verified the ideal application for troubleshooting when documentation is missing or incomplete.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.10
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• pp.2187-2193
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• 2010

A specific radar system can be implemented more easily using the frequency modulated continuous wave comparing with the pulse Doppler radar. It also has the advantage of LPI (low probability of interception) because of the low power and wide bandwidth characteristics. These radars are usually used to cover the short range area and to obtain the high resolution measurements of the target range and velocity information. The transmitted waveform is used in the mixer to demodulate the received echo signal and the resulting beat signal can be obtained. This beat signal is analyzed using the FFT method for the purpose of clutter removal, detection of a target, extraction of velocity and range information, etc. However, for the case of short signal acquisition time, this FFT method can cause the serious leakage effect which disables the detection of weaker echo signals masked by strong side lobes of the clutter. Therefore, in this paper, the weighting window method is analyzed to suppress the strong side lobes while maintaining the proper main lobe width. Also, the results of FFT beat spectrum analysis are shown under various environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.6
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• pp.350-356
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• 2014

In this paper, we design a local signal to improve a tracking performance of time-multiplexed binary offset carrier (TMBOC) signal, which was adopted in modernized global positioning systems (GPS). Specifically, considering that TMBOC signal includes BOC(6,1) components, we first obtain local signal by evenly dividing sub-carrier of TMBOC(6,1,4/33) by the period of a BOC(6,1) pulse. Finally, we remove side-peaks of TMBOC(6,1,4.33) autocorrelation via combination of partial correlations given from designed local signal and solve the ambiguity problem. From numerical results, when performing signal tracking using the designed local signal, we demonstrate that the improved tracking error standard deviation (TESD) performance is offered as compared its autocorrelation and the conventional correlation functions.

• Journal of the Korea Computer Industry Society
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• v.3 no.12
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• pp.1651-1658
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• 2002

Recently power cable used generally in Korea, because installation is very simple and it has high stability. It confirms to the requirements of IEEE std. 404-1993 by factory testing, but many problems of insulated cable systems are caused by internal defects of the joint part which have to be mounted ensile. Especially, fault rates are arise from impurities or voids. A suitable solution for a monitoring of power cable during the after-laying test and service is partial discharge detection. The artificial defects between cable joint(EPR) and insulator(XLPE) interface are considered in this research to investigating the partial discharge characteristics. ${\varphi}$-q-n properties were detected using data acquisition system and Maximum charge($q_{max}$), repetition rate(${\={n}$), average charge(${\={q}$), Unbalance rate of ${\={n}$ and ${\={q}$ are calculated in order to analysis partial discharge properties quantitatively from this statistic value.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.2
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• pp.151-164
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• 2003

In this paper, induction motor drives with low switching acoustic noise based on the 2 phase modulated RLL(Random Lead-Lag) PWM is proposed and implemented. The proposed switching method is much bettor than 3 phase modulated RLL-PWM from the standpoint of the broadening effect of the acoustic noise spectrum. Along with the randomization of PWM Pulses, SVM(Space Vector Modulation) is executed in the TMS320C31 DSP(Digital Signal Processor). To verify the validity of the proposed RPWM(Random PWM), the experimental study was tried. The experimental results show that the performance of the proposed method and the 3 phase center-aligned SVM / conventional RLL-PWM are nearly the same from the viewpoint of the constant v/f centrel. But, in case of the proposed 2 phase modulated RLL-PWM, the spectrum characteristics of the voltage and the switching acoustic noise are shown to have better broadening effect than 3 phase modulated one.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.10
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• pp.2230-2236
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• 2012

Currently, the AC-to-DC power conversion system using diode rectifiers is mainly used in large vessels. Also, to reduce the total harmonic distortion(THD) of current and voltage, this system requires an additional phase-shifting transformer which can be powered multi-pulses. In this case, due to the installation of the transformer, the spatial or economic loss occurs. This paper presents a novel active rectification scheme using silicon controlled rectifier(SCR) or insulated gate bipolar transistor(IGBT) devices on behalf of the diode rectifiers which are currently operating in large vessels such as LNG Carrier(LNGC). The proposed system can use the low voltage source and reduce current and voltage harmonics generated by nonlinear loads connected to the power distribution bus and save economic costs by removing the phase-shifting transformers which are used in conventional system. Computer simulations are performed under the electric propulsion system which is operating in current large vessel. The results are shown in support of the improvement of THD included in the current and voltage wave forms of propulsion motor.