• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1072-1077
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• 2004

This paper provides a new approach to analyze the stability of a general multi-link TCP Vegas, which is a kind of feedback-based congestion algorithm. Whereas the conventional approaches use the approximately linearized model of the TCP Vegas along equilibrium pints, this approach models a multi-link TCP Vegas network in the form of a piecewise linear multiple time-delay system. And then, based on the exactly characterized dynamic model, this paper presents a new stability criterion via a piecewise and multiple delay-dependent Lyapunov-Krasovskii function. Especially, the resulting stability criterion is formulated in terms of linear matrix inequalities (LMIs).

• Journal of Electrical Engineering and Technology
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• v.3 no.1
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• pp.8-13
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• 2008

Because of the robust nonlinear characteristics appearing in today's modern power system, a strong interaction exists between the angle stability and the voltage stability, which were conventionally studied insularly. However, as the power system is a complex unified system, angle instability always happens in conjunction with voltage instability. The authors propose a novel method to analyze this type of stability problem. In the proposed method, the theory of normal forms of vector fields is utilized to treat the auxiliary dynamic system. By use of this method, the interaction between response modes caused by the nonlinearity of the power system can be analyzed. Consequently, the eigenvalue analysis method is extended to cope with performance analysis of the power system with heavy nonlinearity. The effectiveness of the proposed methodology is verified on a 3-bus power system.

• Proceedings of the KIEE Conference
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• 1998.11b
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• pp.466-468
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• 1998

This paper designs a robust controller with improved stability of a system. Robust control theory has been developed by many researchers. The controller derived in that using robust control theory has an assumption that it will be exactly implementation. But, It is very hard because of truncation errors, D-A, A-D transformation, and finite resolution, etc. Such perturbations would make problems in the stability of the system. Recently, Keel's paper presents some examples which shows controllers based on the robust controller design method are very fragile on its own perturbation. In this paper, we try to improve the stability of the closed-loop system in which there exist perturbation in the plant as well as in the controller. The results shows that the stability is improved and the performance is still satisfied.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.472-475
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• 2001

The electrical properties and stability of ZPCCY-based varistors composing of ZnO-Pr$_{6}$ O$_{11}$ -CoO-Cr$_2$O$_3$-Y$_2$O$_3$ ceramics were investigated with sintering time. As sintering time is increased, the nonlinear exponent decreased in the range of 51.19∼26.70. Among varistors having above 30 in nonlinear exponent, for the varistor sintered for 1h, the nonlinearity was superior to the stability comparatively and, in the case of 2h, the stability was superior to the nonlinearity relatively. Consequently, it is estimated that the varistors sintered for 1∼2h will be applied to various fields by trade-off between nonlinearity and stability.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.787-789
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• 1996

This paper describes a Transient Stability Education & Training Software that can make the students or beginners easily be familiar with power system stability problems. The Major objective of this study is to provide, for educational purpose, an interactive computer graphic tool that can facilitate power system study in highly user-friendly environment. The proposed software is designed to have the particular features such as follow : simulation with animation of the rotor, useful interactive scheme, various graphic illustrations related to critical factors of the stability, trace function including revival simulation with different processing speed. With these features, the software could be suitable for educational and training of students/beginners in power system stability engineering field.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.220-223
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• 2003

This paper presents VSCOPF(Votage Stability Constrained Optimal Power Flow) algorithm based on SLP(Successive Linear Programming) to interpret the large scale system. Voltage stability index used to this paper is L index to be presented by function form. The objective function consists of load shedding cost minimization. Voltage stability indicator constraint was incorporated in traditional OPF formulation. as well as the objective function and constraints are linearlized and the optimal problem is performed by SLP(Successive Linear Programming). In this paper, the effect of voltage stability limit constraint is showed in the optimal load curtailment problems. As a result, an optimal solution is calculated to minimize load shedding cost guaranteeing voltage security level. Numerical examples using IEEE 39-bus system is also presented to illustrate the capabilities of the proposed formulation.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.239-241
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• 2003

The time domain simulation method of transient stability presents accuracy and reliability, but it demands much computational time. Therefore it is necessary to filter out very stable and very unstable cases from a large set of contingencies. Following a disturbance, the shape and magnitude of representative generator angle which is most increased after fault clearing are the measure of transient stability. This paper propose a method that is not a calculation of the exact CCT of contingency, but a fast assessment of transient stability. Also it can help operators identify transient stability immediately without analyzing the graphical results. The proposed method is applied to the KEPCO system. The PSS/E is used as a time domain simulation engine by IPLAN.

• Journal of Electrical Engineering and Technology
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• v.13 no.3
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• pp.1232-1240
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• 2018

This paper aims at designing an intelligent controller, based on control Lyapunov Function strategy integrated with fabricating discrete model of Buck and Boost converters and analyzing energy changes during the DC/DC progress to realize tracing reference current on Buck and Boost converters. In addition, practical stability phenomenon research and transient performance analysis has been proposed to give an insight to the influence of controller parameters in achieving an enhanced output performance and how the time of sample period affect the error of practical stability will be illustrated. The novelty of this controller in comparison to other schemes lies in the improved performance of practical stability.

• Progress in Superconductivity and Cryogenics
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• v.20 no.1
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• pp.19-22
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• 2018

The thermal and electrical properties of the conductor are critical parametersfor the design and optimization of the superconducting magnet. This paper presents simulation code to analyze electrical and thermal stability characteristics of the second generation (2G) high-temperature superconductor (HTS) by varying copper stabilizer thickness. Two types of commercial 2G HTS coated conductor tapes, YBCO and GdBCO were used in this study. These samples were cooled by Liquid Nitrogen ($LN_2$) having boiling at 77.3 K and an equivalent electrical circuit model for them is choosen and analysed in details. Also, an over-current pulse test in which a current exceeding a critical current was performed. From the simulation results, the influences of the copper stabilizer thickness on the stability characteristics of these samples are presented.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1443-1445
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• 1996

Hydrogen passivation enhances the electrical characteristics of poly-Si TFT(Thin Film Transistor). However, the weak Si-H bonds, generated during hydrogenation, degrade the stability of the device. So, we carried out the passivation treatment with $NH_3$ or $N_2$. We compared the effect of $NH_3$ or $N_2$ passivation treatments with that of hydrogenation in terms of stability. Through the $NH_3$ passivation treatment, we obtained the most improved subthreshold swing of 1.2V/decade from the initial subthreshold swing of 1.56V/decade. When electrical stress was given, the $NH_3$ passivated devices showed best electrical stability.