• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 D
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• pp.911-913
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• 1997

This paper presents a method for optima] placement of series capacitors in order to improve the power system transient stability, using genetic algorithms. For the formulation, this paper considers the objective function which is the energy margin as the difference between transient energy and critical energy. The most important factor in determining an accurate critical energy is the controlling unstable equilibrium point (UEP). This paper proposes the controlling UEP methods, concurrently with the DFP(Davidon-Fletcher-Powell) method, which enables the enhancement of multi-machine analysis. The proposed method is applied to 6-bus, 7-line, 4-machine model system to show its effectiveness in determining the locations to install series capacitors and the it's size to be installed in system, simultaneously.

• 한국전자통신학회논문지
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• 제10권9호
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• pp.1039-1048
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• 2015

본 논문에서는 곤충형 다리 구조를 갖는 4족 로봇의 효율적인 계단 보행을 위해 유전 알고리즘(Genetic Algorithm: GA)에 기반한 계단 보행 방법을 제안한다. 제안한 방법에서는 우선 계단 보행을 위한 요소와 도달 영역을 정의한다. 또한 GA 수행을 위한 유전자와 적합도 함수를 설정하고, GA를 이용하여 최소 이동 거리와 최적 에너지 안정도 여유(Energy Stability Margin: ESM)을 갖는 4족 로봇의 착지 지점을 탐색하여 걸음새 궤적을 생성한다. 마지막으로, 컴퓨터 시뮬레이션을 통해 본 논문에서 제안한 계단 보행 방법의 효용성 및 우수성을 검증한다.

• 전기학회논문지
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• 제57권4호
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• pp.567-575
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• 2008

Transient security assessment(TSA) is becoming an essential requirement not only for security monitoring but also for stabilizing control of power systems under new electricity environments. It has already been pointed out that fast transient stability study is an important part for monitoring and controlling system security. In this paper, we discuss an energy function method for stabilizing control of transiently unstable systems by introducing generator tripping system to enhance the transient stability of power systems. The stabilization with less tripped power can be obtained by tripping the generators faster than out-of-synchronism relay. Fast transient stability assessment based on the state estimation and direct transient energy function method is an important part of the stabilizing scheme. It is possible to stabilize the transiently unstable system by tripping less generators before the action of out-of-synchronism relay, especially when a group of generator are going to be out-of-synchronism. Moreover, the amount of generator output needed for tripping can be decided by Transient Energy Function(TEF) method. The main contribution of this paper is on the stabilizing scheme which can be running in the Wide Area Control System.

• Journal of Mechanical Science and Technology
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• 제16권2호
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• pp.227-234
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• 2002

Large superconducting magnets such as ITER (International Thermonuclear Experimental Research) or KSTAR (Korean Superconducting Tokamak Advanced Research) magnet system adopted a cable-in-conduit conductor (CICC) using a forced-flow cooling system. Main optimization criteria for the conductor design of superconducting magnet system are stability margin and CICC cooling requirements. A zero-dimensional method is applied for the calculation of stability and the conductor optimization. In order to increase conductor performance, three different strands, ITER HP-I and HP-II, and KSTAR HP-Ⅲ, are tested. The strand characteristics of KSTAR HP-Ⅲ are measured in the Samsung's PPMS and Jc measurement system, and applied for this study. Also, the strand diameters, 0.81 mm and 0.78 mm are considered for this study, due to design change. Based on this result, the proposed configuration of CICC has been fabricated.

• 조명전기설비학회논문지
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• 제24권10호
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• pp.21-25
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• 2010

This paper explains hybrid method that combines Time domain simulation technique with the direct method of Transient stability analysis. First, it calculate trajectory of real system by Time domain Simulation using OOP(Object Oriented Programming method) and evaluate Transient Energy Function to induce stability index to calculate Transient stability margin. Once the status of system(stable or unstable) has been identified, proper criteria are proposed to stop time-domain simulation to reduce CPU time.

• Journal of Electrical Engineering and Technology
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• 제4권4호
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• pp.443-450
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• 2009

This paper deals with the design of decentralized controller for load-frequency control of interconnected power systems with superconducting magnetic energy storage units and Governor Dead Band Nonlinearity using Multi-Objective Evolutionary Algorithm. The superconducting magnetic energy storage unit exhibits favourable damping effects by suppressing the frequency oscillations as well as stabilizing the inter-area oscillations effectively. The proposed control strategy is mainly based on a compromise between Integral Squared Error and Maximum Stability Margin criteria. Analysis on a two-area interconnected thermal power system reveals that the proposed controller improves the dynamic performance of the system and guarantees good closed-loop stability even in the presence of nonlinearities and with parameter changes.

• 한국군사과학기술학회지
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• 제23권4호
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• pp.355-362
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• 2020

EFP composed of explosive, charge and liner generally penetrates standoff a target by Monroe effect. Its performance highly depends on penetrator characteristics and flight stability. Penetration ability can be dramatically reduced when the penetrator reaches the target with AOA, even if the penetrator has high kinetic energy and L/D ratio. Therefore, it is important to research not only penetrator characteristics and but also flight stability. In this work, the effect of liner shape on penetrator characteristics was examined using free flight test and numerical tools. It was found that tip velocity of penetrator was increased with decreasing liner thickness. It was also found that thicker liner had higher static margin leading to better flight status.

• Journal of Electrical Engineering and Technology
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• 제6권2호
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• pp.161-166
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• 2011

This paper proposes an algorithm for determining critical generator lists using accelerating power and synchronizing power coefficient (SPC), and critical generator group (CGG) from CGG candidates, which is a combination of critical generators. The accurate determination of CGG provides a more accurate energy margin while providing system operator with information of possible unstable generator group. Classical transient energy function (TEF) method selects the critical generators with big corrected kinetic energy of each generator at the moment of fault removal. However, the generator with small acceleration after fault, that is, the generator with small corrected kinetic energy, is also likely to belong to CGG if the generator has small synchronizing power. The proposed algorithm has been verified to be effective compared with the classical TEF method. We utilized the power system of Korean Electric Power Corporation(KEPCO) as a test system.

• 전기학회논문지
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• 제62권11호
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• pp.1495-1504
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• 2013

Renewable energy integration and increased system complexities make system operator maintain supply and demand balance harder than before. To keep the grid frequency in a stable range, an appropriate spinning reserve margin should be procured with consideration of ever-changing system situation, such as demand, wind power output and generator failure. This paper propose a novel concept of dynamic reserve, which arrange different spinning reserve margin depending on time. To investigate the effectiveness of the proposed dynamic reserve, we developed a new short-term reliability criterion that estimates the probability of a spinning reserve shortage events, thus indicating grid frequency stability. Uncertainties of demand forecast error, wind generation forecast error and generator failure have been modeled in probabilistic terms, and the proposed spinning reserve has been applied to generation scheduling. This approach has been tested on the modified IEEE 118-bus system with a wind farm. The results show that the required spinning reserve margin changes depending on the system situation of demand, wind generation and generator failure. Moreover the proposed approach could be utilized even in case of system configuration change, such as wind generation extension.

• Journal of Electrical Engineering and Technology
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• 제13권5호
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• pp.1798-1806
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• 2018

When a contingency occurs in a large transmission route in a power system, it can generate various instabilities that may lead to a power system blackout. In particular, transient instability in a power system needs to be immediately addressed, and preventive measures should be in place prior to fault occurrence. Measures to achieve transient stability include system reinforcement, power generation restriction, and generator tripping. Because the interpretation of transient stability is a time domain simulation, it is difficult to determine the efficacy of proposed countermeasures using only simple simulation results. Therefore, several methods to quantify transient stability have been introduced. Among them, the single machine equivalent (SIME) method based on the equal area criterion (EAC) can quantify the degree of instability by calculating the residual acceleration energy of a generator. However, method for generator tripping effect evaluation does not have been established. In this study, we propose a method to evaluate the effect of generator tripping on transient stability that is based on the SIME method. For this purpose, the measures that reflect generator tripping in the SIME calculation are reviewed. Simulation results obtained by applying the proposed method to the IEEE 39-bus system and KEPCO system are then presented.