• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.665-666
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• 2008

Inserted HTS (high temperature superconducting) coil is promisingly expected as a solution for achievement of higher fields such as GHz scale NMR magnet. However, HTS magnet causes persistent current decay in the persistent current mode and this decay should be compensated in order to keep stable magnetic field. As a solution for the decay in the HTS magnets, we proposed a new type superconducting power supply, i.e., linear type magnetic flux pump (LTMFP). The LTMFP mainly consists of DC bias coil, 3-phase AC coil and superconducting Nb foil. The compensating current in closed superconductive circuit can be easily controlled by the intensity of 3-phase AC current and its frequency. In this study, it has been investigated that the flux pump can effectively charge the current for various frequencies according to the different load magnets.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1779-1780
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• 2008

This paper presents a switching system of speed controller between PI (Proportional_Integrator) and P_LPF (Proportional_Low pass filter) to improve overshoot and slow settling time in DC motor. When the integrator is saturated in the PI controller, the error signal is integrated continuously. For preventing the state, the Anti-windup scheme is proposed. But the Anti-windup scheme dose not show stable characteristics in the whole speed command section after tuned a gain. By using P_LPF switching system these problems are improved and there is no need to tune of user hereafter, when the integrator is saturated. The proposed method is verified by the simulation results using MATLAB SIMULINK.

• Journal of the Korean institute of surface engineering
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• v.28 no.6
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• pp.376-385
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• 1995

Copper-chromium multilayers with a nominal bilayer thickness of about 400 $\AA$ (200 $\AA$ each) were prepared by dc magnetron sputtering and the evolution of microstructure during heat treatment was investigated by using x-ray diffractometry(XRD), Auger electron spectroscopy(AES) and transmission electron microscopy(TEM). It was observed that an amorphous phase with a thickness of about 40 $\AA$ was formed at the interfaces of the as-deposited Cu/Cr multilayered film using cross-sectional TEM. At elevated temperatures, the Cu(111) reflection showed increasing intensity and decreasing line-width as a result of copper grain growth. The intermixed amorphous phase disappeared after annealing at $250^{\circ}C$ for 1 h and the multilayer structure was stable up to $400^{\circ}C$ for 1 h annealing. At $600^{\circ}C$ annealing, it was observed that the multilayer structure was completely destroyed and copper and chromium phases were fully intermixed.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.10
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• pp.161-167
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• 2001

This paper presents an approach to nonlinear engine idle controller and intake manifold absolute pressure(MAP) observer based on mean torque production model. A stable engine idle speed is important in that the unstable engine Idle mode can make engine to drooping or stall state. A sliding fuzzy controller has been designed to control engine idle speed under load disturbance. A sliding observer is also developed to estimate the intake manifold absolute pressure and compared with the actual MAP sensor value. The sliding mode observer has shown good robustness and good tracking performance. The inputs of sliding fuzzy controller are the errors of rpm and MAP. The output is a duty cycle(DC) for driving a idle speed control valve(ISCV).

• The Transactions of the Korean Institute of Electrical Engineers
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• v.36 no.1
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• pp.3-8
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• 1987

The conventional autosequentially commutated current-fed inverter (ASCI) is widely employed with the induction motor drives for speed control. Howener, this inverter has a limit of high power and high frequency indution motor drives. One of the limitations is to be found in the commutation capacitors in the main circuit of this inverter. A new current-fed gate turn-off thyristor (GTO) inverter is developed. This inverter is composed of the main GTO bridge configuration and the improved energy rebound circuit (ERC)without the commutation capacitor. This inverter works stable at high frequency from light load to heavy one. The improved ERC is used not only to rebound the load reactive power to the dc link, but also to return the power in the load to the ac source. The new GTO inverter circuit and the characteristics of the inverter induction motor drives are explained and analyzed.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.7
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• pp.855-862
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• 1999

A high speed digital distance relaying algorithm based on a least square error method is proposed. To obtain stable phasor values very quickly, first, a lowpass filter which has very short transient period and no overshoot is presented. Secondly, the least square error method having the data window of 3 samples is used by applying a FIR filter which removes the DC-offset component in current relaying signals. Test results show that the proposed distance relaying algorithm detects most of internal faults within a half cycle after faults in a 154[kV] overhead transmission line system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.268-271
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• 2002

The goal of the research is to study and describe a new stressed state of High Temperature Superconducting (High-Tc) YBCO Films, to create of SQUIDs (Superconducting Quantum Interference Device) on the bases of these Films with maximal sensitivity. The experimental investigation of the stressed films grown by laser ablation method and its properties, the fabrication of the dc-SQUIDs with maximal sensitivity on the bases of the stressed YBCO films were carried out. The stressed film having the value of the critical current density $J_{c}=3{\cdot}10^{5}A/cm^{2}$ was the more stable than others.

• Journal of the Korean Solar Energy Society
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• v.26 no.1
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• pp.57-64
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• 2006

Cr-CrO cermet solar selective coatings with a double cermets layer film structure were prepared using a special direct current (dc) magnetron sputtering technology. The typical films structures from surface to bottom substrate were measured to be an $Al_2O_3$ anti-reflection layer on a double Cr-CrO cermet layer on an Al metal infrared reflection layer. Optical properties of optimized Cr-CrO cermet solar selective coating were absorptance (${\alpha}$) = 0.95 and emittance (${\varepsilon}$) = 0.10 ($100^{\circ}C$). Atomic force microscopy (AFM) image showed that Cr-CrO cermet film was very smooth and their grain size was also very small The results of thermal stability test showed that the Cr-CrO cermet solar selective coatings were stable for use at temperature of $400^{\circ}C$.

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.126-128
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• 2018

Solar array simulator (SAS) is a special DC power supply that regulates the output voltage or current to emulate characteristics of photovoltaic (PV) panels. Especially, the control of SAS is a challenging task due to the nonlinearity in the output curve, which is dependent on irradiance as well as temperature and is determined by panel materials. Conventionally, both current-mode control and voltage-mode control should be alternated by partitioning the operating curve into multiple sections, which is not only for the measurement noise problem with the feedback sensing but also for the control stability issue near the maximum power point. However, the occurrence of transition among different controllers may deteriorate the overall performance. To eliminate the mode transitions, a novel single controller scheme has been introduced in this paper, where the reference operating projection technique enables simple, smooth and numerically stable control. Theoretical consideration on the loop stability issue is discussed and the performance is verified experimentally for the emulation of a PV panel data in view of stability and response speed.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.691-692
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• 2009

Screen printable CNT pastes were formulated including conductive nano particles (CNPs) and their properties were investigated with an expectation of stable cold cathodes for advanced lamp application. CNT cathodes showed a turn-on field of 1~1.5V/um, a life time of ~100 hours at an emission current density of 10uA/$cm^2$ for DC-bias. Detailed analysis of measured I-V was carried out by applying Fowler-Nordheim model to trace down the origin of emission property degradation.