• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.2B no.3
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• pp.133-139
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• 2002

In this paper, a prototype of an active auxiliary quasi-resonant DC link (QRDCL) snubber assisted voltage source bidirectional power converter (AC to DC and DC to AC) operating at zero voltage soft-switching (BVS) PWM nlode is presented for a Battery Energy Storage System (BESS). The operating principle of this QRDCL circuit and multifunctional control-based converter system, including PWM inverter mode in which energy flows from the battery bank to the three-phase utility-grid in addition to an active PWM converter mode in which energy flows from the utility-grid to the battery banks are described respectively by the control implementation on the basis of d-q coordinate plane transformation. The multifunctional operation characteristics of this three-phase ZVS PWM bi-directional converter with QRDCL is demonstrated fer a BESS under the power conditioning and processing schemes of energy supply mode and energy storage mode, and compared with a conventional three-phase hard switching PWM bi-directional converter for a BESS. The effectiveness of the three-phase ZVS PWM hi-directional converter with QRDCL is proven via the simulation analysis.

• Proceedings of the KIEE Conference
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• 2007.10c
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• pp.182-184
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• 2007

이 논문에서는 계통연계형 3KW 태양광 발전 시스템 개발에 필요한 기본적인 요소기술로서 MPPT(Maximum Power Point Tracking), 계통연계를 위한 단상 PLL(Phase Locked Loop), 피크전압검출법과 전류제어기법 등을 살펴보고 이를 시뮬레이션으로 검증하였다. 또한 검증된 기법등을 토대로 3kW 태양광 발전 PCS(Power Conditioning System)에 적용실험을 통해 결과를 확인하였다.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.4
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• pp.405-414
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• 2011

Recently, the development of several hundreds of kW scale PCS for fuel cell generation is required as commercialization process of distributed generation systems using high temperature fuel cells such as MCFC begins. This paper proposes and optimized topology suitable for MCFC fuel cell generation system and LCL filter design method considering voltage quality of local loads such as MBOP. An interleaving technique is applied to step-up DC-DC converter, optimized number of phases is determined considering efficiency and volume. Also, a LCL filter design method is proposed considering quality of current injected to the grid as well as that of voltage across the local load. The proposed PCS system is validated through reduced 1kW prototype.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.2
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• pp.360-369
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• 2008

The solar cells should be operated at the maximum power point because its output characteristics were greatly fluctuated on the variation of insolation, temperature and load. It is necessary to install an inverter among electric power converts by means of the output power of solar cell is DC. The inverter is operated supply a sinusoidal current and voltage to the load and the interactive utility line. In this paper, the proposes a photovoltaic system is designed with a step up chopper and single phase PWM voltage source inverter. Synchronous signal and control signal was processed by one-chip microprocessor for stable modulation. The step up chopper is operated in continuous mode by adjusting the duty ratio so that the photovoltaic system tracks the maximum power point of solar cell without any influence on the variation of insolation and temperature for solar cell has typical dropping character. The single phase PWM voltage source inverter is consists of complex type of electric power converter to compensate for the defect, that is, solar cell cannot be develop continuously by connecting with the source of electric power for ordinary using. It can be cause the efect of saving electric power, from 10 to 20%. The single phase PWM voltage source inverter operates in situation, that its output voltage is in same phase with the utility voltage. The inverter are supplies an ac power with high factor and low level of harmonics to the load and the utility power system.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.6
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• pp.568-576
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• 2004

This paper presents a new anti-islanding method for distributed power generation system (DPGS) using renewable energy. Based on the concept of real and reactive power mismatch, three different islanding conditions are analyzed. It is shown via analysis that islanding voltage is a function of real power alone, where as its frequency is a function of both real and reactive power. Using this analysis, a new anti-islanding method is developed. The proposed protection algorithm continuously perturbs ($\pm$5%) the reactive power supplied by DPGS while simultaneously monitoring the utility voltage and frequency. If a measurable frequency deviation took place by islanding, the real power of DPGS is further reduced to 80%. This detection method is shown to be fast acting under resonant loads. Possible islanding conditions are simulated and verified with analysis. Experimental results on a 0.5kW utility-interactive fuel cell system are suggested.

• Journal of the Korea Society of Computer and Information
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• v.20 no.5
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• pp.41-51
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• 2015

In order to hide their identities, intruders on the Internet often attack targets indirectly by staging their attacks through intermediate hosts known as stepping stones. In this paper, we propose a brute-force technique to detect the stepping stone behavior on a Linux server where some shell processes remotely logged into using interactive services are trying to connect other hosts using the same interactive services such as Telnet, Secure Shell, and rlogin. The proposed scheme can provide an absolute solution even for the encrypted connections using SSH because it traces the system calls of all processes concerned with the interactive service daemon and their child processes. We also implement the proposed technique on a CentOS 6.5 x86_64 environment by the ptrace system call and a simple shell script using strace utility. Finally the experimental results show that the proposed scheme works perfectly under test scenarios.

• Journal of the Korean Institute of Landscape Architecture
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• v.24 no.3
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• pp.29-41
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• 1996

The purposes of this study were to develope some techniques which can be used in the landscape simulation process using PC based computer grahics. As a result, a couple of utilities were programmed in AutoLISP language. The one(DSLINE.LSP) is to digitize 2-dimensional structuer forms in the interactive mode considering error handling, and the other one (IMPOST.LSP) is for superimposing and visualizing the digitized plan data to 3-dimension solids & surfaces referring to topographic elevations of meshes in digital terrain model. By applying utilities to present site, the followings may be described. 1) The utility DSLINE.LSP for digitizing simplified building structure form were proved to be easy to input data of polygons including orthogonal edges by handling user coordinates system and checking invalid intersection and default colsing. 2) IMPOST.LSP utility for superimposing and visualizing tool were proved to be more complicated and speedy in calculating process compared with a practical application of modeling tool before rendering process in landscape simulation of built environment on topographic relief, on specially mesospace level of assessment.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.26 no.4
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• pp.72-81
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• 2003

The purpose of this paper is to propose an interactive method, which is designed to select the optimal preferred alter-native for the MLDM(Multiple-the Larger-the better type Decision-Making) problems with the-larger-the-better quality characteristics. The basic idea of the paper is essentially to eliminate inefficient alternative based on the concept of Taguchi Signal-to-Noise ratios and the cutting range instead of using UVF(Utility/value Function) on the group of attributes that can be considered importantly by the decision makers. As a result, the method proposed in the paper for MLDM problems can be significant in that the change of characteristics is transformed into the size of Signal-to-Noise ratio, which can be relatively easy to understand by decision makers.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.4
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• pp.208-216
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• 2005

Recently, the study of islanding phenomenon, maintains its operation even when the utility grid is removed has lead to the trend of utility interactive inverters in photovoltaic generation systems. In this paper, a novel Anti-islanding method is presented. the proposed method can keep the real average power component constant by MPPT control and cause the load current frequency with only change of reactive power component under the islanding condition. its periodical change of Reactive power component can decrease the NDZ(Non-Detective zone) so that the detection of various loads will be possible. the insufficient effect if additional reactive power component to the grid is proved theoretically and the islanding detection is also confirmed from a experimental result with a inverter for 3kW photovoltaic generation system applied the proposed Anti-islanding method.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.571-575
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• 2002

Generation of electrical energy faces many problems today. Solar power converters were used to convert the electrical energy from the solar arrays to a stable and reliable power source. The object of this paper is to analyze and design DC-DC converters in a solar energy system to investigate the performance of the converters. A DC-DC converter can be commonly used to control the power flow from solar cell to load and to achieve maximum power point tracking(MPPT), DC-AC converter can also be used to modulate the DC power to AC power being applied on common utility load. A DC-DC converter is used to boost the solar cell voltage to constant 360(V) DC link and to ensure operation at the maximum power point tracking, If a wide input voltage range has to be covered a boost converter is required. In this paper, author described that simulation and experimental results of PV system contain solar modules, a DC-DC converter(boost type chopper), a DC-AC converter (3-phase inverter) and resistive loads.