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초고속 위성통신을 위한 IF 모듈 설계 및 제작에 관한 연구
서철헌 崇實大學校 生産技術硏究所 2001 論文集 Vol.31 No.-
As the bandwidth in increased, the difference in frequency between a DC and desired siginal is decreased. It indicates the difficult design of a band pass filter for reject to a LO leakage signal and a image signal. This thesis study the suppression of a LO leakage. The research is applied in the Ka Band satellite communication ATM module with a 155Mbps signal bandwidth. This study use a Sub Harmonic Image Rejection Mixer for a LO suppression.
서철헌 崇實大學校 2000 論文集 Vol.30 No.1
In this paper, a 1*4 active phased array antenna was designed using the voltage controlled oscillators(VCO) with the varactor diode and the transmission line network with open stub. The varactor diode was connected in parallel to the FET for the wide tuning range of the VCO and the open stubs were connected at the end of the transmission line network to increase the scan range. The scan range, -20 degree to 22 degree at 2.44GHz, was controlled by the applied varactor diode voltage and the transmission line coupling network.
서철헌 崇實大學校 生産技術硏究所 2002 論文集 Vol.32 No.-
In this paper, the design of dual mode power amplifier that operates on wireless LAN and IMT-2000 service is described. Final output is 1watt. Two different active components are used for the dual mode operation, and they are combined with the bias control circuits. By the voltage variation of the mode control voltage V_m, the conversion between two modes are achieved. When the control voltage is low, the amplifier is operated at the band of wireless LAN, oppositely, when the control voltage is high, the amplifier is operated at the band of IMT-2000. Two output ports was combined with the circuit using Photonic Band Gap pattern and bandpass filter.
Seo, Hun-Chul,Kim, Chul-Hwan The Korean Institute of Electrical Engineers 2012 Journal of Electrical Engineering & Technology Vol.7 No.4
Use of photovoltaic (PV) power generation system will become more widespread in the future due to anticipated cost reduction in PV technology. As the capacity of PV systems increases, a variation of power system frequency may prevent the stable output of PV system. However, the standard for the frequency protection of distributed generation in Korea Electric Power Corporation (KEPCO)'s rule does not include the setting of frequency protection. Therefore, this paper analyzes the correlation between the frequency protection requirements and the stability of grid-connected PV system for the adjustable operating setting of frequency protection. The distribution system interconnected with 3 MW PV system is modeled by Matlab/Simulink. The various values of frequency are simulated. For studied cases, the stability of PV system is analyzed. It is concluded that the setting of frequency protection is necessary to consider the stability of PV system.
Analysis of Magnitude and Rate-of-rise of VFTO in 550 kV GIS using EMTP-RV
Seo, Hun-Chul,Jang, Won-Hyeok,Kim, Chul-Hwan,Chung, Young-Hwan,Lee, Dong-Su,Rhee, Sang-Bong The Korean Institute of Electrical Engineers 2013 Journal of Electrical Engineering & Technology Vol.8 No.1
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.
Applicability of Messenger Wire for Purpose of Lightning Protection
Hun-Chul Seo,Joon-Han,Sun-Kyu Choi,Byung-Sung Lee,Sang-Bong Rhee,Chul-Hwan Kim 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.1
The Korean distribution line currently consists of overhead ground wires (OHGW), overhead distribution lines, neutral wires (NW), and messenger wires (MW). The MW is installed under the NW. The lightning protection system in Korea is focused on OHGW and lightning arrester and the MW are not considered. Therefore, this paper proposes the applicability of MW for purpose of lightning protection. For this, we analyzed the effects of lightning overvoltage according to the existence of OHGW and MW and the grounding conditions of the MW in the Korean distribution system. The grounding conditions of the MW that we took into consideration were the common or separate grounding of the MW and NW. The analysis based on the equivalent circuit of the distribution pole at each condition was performed. The distribution lines and lightning were modeled using the Electromagnetic Transients Program (EMTP). For each of the installation conditions of the OHGW and MW, the various lightning conditions were simulated and analyzed for both direct and indirect lightning. The simulation results showed that, if the OHGW was not installed in the Korean distribution system, the lightning overvoltage could be reduced by the common grounding of the MW and NW.
Hun-Chul Seo,Chul-Hwan Kim,Sang-Bong Rhee,Jae-Chul Kim,Ok-Bae Hyun IEEE 2010 IEEE transactions on applied superconductivity Vol.20 No.4
<P>A conventional superconducting fault current limiter (SFCL) is usually only connected to a power system for fault current limitation. The study described in this paper, however, attempts to use the hybrid SFCL application to reduce the transformer inrush current. To accomplish this, this paper first suggests the concepts to expand the scope of the SFCL application in the power system. The power system operator should first determine the proper amount of current-limiting resistance (CLR) of the hybrid SFCL. Therefore, this paper suggests a decision scheme of the optimal insertion resistance in an SFCL application to reduce the transformer inrush current. This scheme and the SFCL model are implemented using the electromagnetic transient program (EMTP). We determine the optimal CLR by EMTP simulation, and this value is applied to model the SFCL by the EMTP. The simulation results show the validity and effectiveness of the suggested scheme and the ability of the SFCL to reduce the inrush current.</P>
Hun-Chul Seo,Chul-Hwan Kim 대한전기학회 2012 Journal of Electrical Engineering & Technology Vol.7 No.4
Use of photovoltaic (PV) power generation system will become more widespread in the future due to anticipated cost reduction in PV technology. As the capacity of PV systems increases, a variation of power system frequency may prevent the stable output of PV system. However, the standard for the frequency protection of distributed generation in Korea Electric Power Corporation (KEPCO)’s rule does not include the setting of frequency protection. Therefore, this paper analyzes the correlation between the frequency protection requirements and the stability of grid-connected PV system for the adjustable operating setting of frequency protection. The distribution system interconnected with 3 ㎿ PV system is modeled by Matlab/Simulink. The various values of frequency are simulated. For studied cases, the stability of PV system is analyzed. It is concluded that the setting of frequency protection is necessary to consider the stability of PV system.