• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.3
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• pp.6-11
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• 2006

This paper describes the novel control techniques design of VSC(Voltage Sag Corrector) for the purpose of power line quality enhancement. A fast detecting technique of voltage sag is implemented through the detection of instantaneous value on synchronous rotating dq-reference frame. The first order digital filter is added in the detection algorithm to protect the insensitive characteristics against the noise. The relationship between the total detection time and cut-off frequency of the filter is described. The size of the capacitor bank used as the energy storage element is designed from the point of view of input/output energy with circuit analysis. Finally, the validity of the proposed scheme is proven through the simulated results.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.207-210
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• 2005

This paper describes a design of several ship's emergency lighting system(SELS) that power factor is improved and power is controlled extensively, and techniques to control and monitor this system in remote distance by PC serial communication. The remote monitoring control system is composed of emergency power supply system (EPSS), half bridge(HB)inverter, fluorescent lamp(FL), microprocessor, multi communication interface. EPSS checks the voltage of the emergency backup battery in real time. In case that the voltage of 13[V] or less has been detected for 5[msec] or longer for 3 times in a row, charger circuit is connected for battery charging. Experimental works using proposed system confirm that speedy and stable power to be supplied when main power source cut-off, compared with conventional analog type, and input power up to 35.0[%] by adjusting of pulse frequency of the HB inverter.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.2
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• pp.88-92
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• 2006

We present a microfluidic system with microvalves and a micropump that are easily integrated on the same substrate using the same fabrication process. The fabricated microfluidic system is suitable for use as a disposable device and its characteristics are optimized for use as a micro chemical analysis system (micro-TAS) and lab-on-a-chip. The system is realized by means of a polydimethylsiloxane (PDMS)-glass chip and an indium tin oxide (ITO) heater. We demonstrate the integration of the micropump and microvalves using a new thermopneumatic-actuated PDMS-based microfluidic system. A maximum pumping rate of about 730 nl/min is observed at. a duty ratio of 1 $\%$ and a frequency of 2 Hz with a fixed power of 500 mW. The measured power at flow cut-off is 500 mW for the microvalve whose channel width, depth and membrane thickness were 400 $\mu$m, 110 $\mu$m, and 320 $\mu$m, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7B
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• pp.606-612
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• 2012

Visible light communications (VLC) uses modern solid-state LEDs to broadcast information. Emerging white-light LEDs allows the combination of lighting and optical wireless communication in one optical source. In this paper, a new LED lighting using one-chip-type white LED is proposed for efficient illumination and optical wireless communications. Performance analysis such as horizontal illuminance, 3-dB cut-off frequency, inter-symbol interference, signal-to-noise ratio and bit-error rate shows the effects of the shapes of LED lighting. Performance of the proposed LED lighting under the existence of obstacles is superior to that of the existing LED lighting in illumination and optical wireless communication.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.208-211
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• 2005

This paper presents an ultra-low partial discharge(PD) measurement system that has been accepted as a non-destructive method to estimate electrical insulation of low-voltage electric devices. The PD measurement system is composed of a coupling network, a low noise amplifier, and associated electronics. A shielding box is used to make a better condition against electromagnetic interference. A low cut-off frequency of the coupling network was 1MHz(-3 dB). Calibration tests on laboratory set-up have shown that the PD measurement system has a stable sensitivity of 11.4mV/pC. In an application experiment on a low-voltage induction motor(5HP), we could detect 0.77pC level of partial discharge pulse at the applied voltage of AC 664 V$_{peak}$.

• Nuclear Engineering and Technology
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• v.50 no.8
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• pp.1246-1254
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• 2018

The importance of performing Level 3 probabilistic safety assessments (PSA) along with a general interest in assessing multi-unit risk has been sharply increasing after the Fukushima Daiichi nuclear power plant (NPP) accident. However, relatively few studies on multi-unit Level 3 PSA have been performed to date, reflecting limited scenarios of multi-unit accidents with higher priority. The major difficulty to carry out a multi-unit Level 3 PSA lies in the exponentially increasing number of multi-unit accident combinations, as different source terms can be released from each NPP unit; indeed, building consequence models for the astronomical number of accident scenarios is simply impractical. In this study, a new approach has been developed that employs the look-up table method to cover every multi-unit accident scenario. Consequence results for each scenario can be found on the table, established with a practical amount of effort, and can be matched to the frequency of the scenario. Preliminary application to a six-unit NPP site was carried out, where it was found that the difference between full-coverage and cut-off cases could be considerably high and therefore influence the total risk. Additional studies should be performed to fine tune the details and overcome the limitations of the approach.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.4_1
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• pp.377-385
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• 2021

High voltage direct current(HVDC) systems has been an alternative method of a power transmission to replace high voltage alternate current(HVAC), which is a traditional AC transmission method. Due to technical limitations, Line commutate converter HVDC(LCC-HVDC) was mainly used. However, result from many structural problems of LCC-HVDC, the voltage source converter HVDC(VSC-HVDC) are studied and applied recently. In this paper, after analyzing the reactive power and output voltage ripple, which are the main problems of LCC-HVDC, the characteristics of each HVDC are summarized. Based on this result, a new LCC-HVDC structure is proposed by combining LCC-HVDC with the MMC structure, which is a representative VSC-HVDC topology. The proposed structure generates lower reactive power than the conventional method, and greatly reduces the 12th harmonic, a major component of output voltage ripple. In addition, it can be easily applied to the already installed LCC-HVDC. When the proposed method is applied, the control of the reactive power compensator becomes unnecessary, and there is an advantage that the cut-off frequency of the output DC filter can be designed smaller. The validity of the proposed LCC-HVDC is verified through simulation and experiments.

• Journal of electromagnetic engineering and science
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• v.1 no.1
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• pp.73-77
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• 2001

We studied the fabrication of GaAs-based pseudomorphic high electron mobility transistors(PHEMT`s) for the purpose of millimeter- wave applications. To fabricate the high performance GaAs-based PHEMT`s, we performed the simulation to analyze the designed epitaxial-structures. Each unit processes, such as 0.1 m$\mu$$\Gamma$-gate lithography, silicon nitride passivation and air-bridge process were developed to achieve high performance device characteristics. The DC characteristics of the PHEMT`s were measured at a 70 $\mu$m unit gate width of 2 gate fingers, and showed a good pinch-off property ($V_p$= -1.75 V) and a drain-source saturation current density ($I_{dss}$) of 450 mA/mm. Maximum extrinsic transconductance $(g_m)$ was 363.6 mS/mm at $V_{gs}$ = -0.7 V, $V_{ds}$ = 1.5 V, and $I_{ds}$ =0.5 $I_{dss}$. The RF measurements were performed in the frequency range of 1.0~50 GHz. For this measurement, the drain and gate voltage were 1.5 V and -0.7 V, respectively. At 50 GHz, 9.2 dB of maximum stable gain (MSG) and 3.2 dB of $S_{21}$ gain were obtained, respectively. A current gain cut-off frequency $(f_T)$ of 106 GHz and a maximum frequency of oscillation $(f_{max})$ of 160 GHz were achieved from the fabricated PHEMT\\`s of 0.1 m$\mu$ gate length.h.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.3
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• pp.355-360
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• 2012

In this paper, an stepped-impedance low pass filter(SI-LPF) of triangular-patch type is proposed. A SI-LPF designed according to the standard SI-LPF design procedure is folded as a right angled triangle. The figure of merits of this structure are the adjustabilities of the cut off frequency, the stopband and the attenuation pole frequency of the proposed LPF by varying the resultant slots after folding the SI-LPF compactly for miniaturization. The size of the fabricated LPF is $13.75mm{\times}6.875mm$, which is 24.4 % reduced one compared to that of the conventional SI-LPF. The measured results of the LPF show return loss of less than -10 dB at passband, insertion loss of less than -10 dB at stopband and wide stopband from 3.5 GHz to 10 GHz (about $3f_c$).

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.9
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• pp.25-30
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• 2004

In this Paper, the 0.1 w InGaAs/InAlAs/GaAs Metamorphic HEMT, which is applicable to MIMIC, and a 100 GHz MIMIC amplifier were designed and fabricated. The DC characteristics of MHEMT are 640 mA/mm of drain current density, 653 mS/mm of maximum transconductance. The current gain cut-off frequency(fT) is 173 GHz and the maximum oscillation frequency(fmax) is 271 GHz. A 100 GHz amplifier was designed using 0.1${\mu}{\textrm}{m}$ MHEMT and CPW technology. The measured results from the 100 GHz MIMIC amplifiers show good S21 gain of 10.1 dB and 12.74 dB at 100 GHz and 97.8 GHz, respectively.