• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.1
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• pp.68-75
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• 2013

This paper presents a scheme to improve transient stability using Newton's Approach for generation rescheduling. For a given contingency, the energy margin and sensitivities are computed. The bigger energy margin sensitivity of generator is, the more the generation of the generator effects to the transient stability. According to energy margin sensitivity, the control variables of generation rescheduling are selected. The fuel cost function is used as objective function to reallocate power generation. The results are compared to the results of time simulation to show its the effectiveness.

• Journal of Korean Society of Steel Construction
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• v.8 no.3 s.28
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• pp.55-65
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• 1996

For stability analysis of stifened rectangular thin plates with various boundary conditions, Ritz method is presented. An energy method is especially useful in those cases where a rigorous solution of the diferential eqution is unknown or where we have a plate reinforced by stiffeners and it is required to find only an approximate value of the critical load. The strain energy due to the plate bending and the work done by the in-plane forces are taken into account in order to apply the principle of the minimum potential energy. The buckling mode shapes of flexural beams with various boundary conditions are derived, and shape functions consistent with the given boundary conditions in the two orthogonal directions are chosen from those displacement functions of beams. The matrix equations for stability of stiffened rectangular thin plates are determined from the stationary condition of the total potential energy. Numerical example for stability behaviors of horizontally and vertically stiffened plates subjected to uniform compression, bending and shear loadings are presented and the obtained results are compared with other researchers' results.

• The Journal of Korean Medicine
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• v.33 no.3
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• pp.105-119
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• 2012

Background: In contrast to the increased interest in constitutional medicine evidenced by clinical experiences, there has been no theoretical or mathematical analysis on the stability or number of constitutional types. Objectives: The purpose of the study was to evaluate the stability of possible constitutional types and to find stable constitutional types based on imbalanced structure of five energy elements using mathematical analysis. Methods: For the 120 constitutional types which are possible by the imbalanced combination of five energy elements, vitality, stability and continuity were evaluated mathematically based on mutual activation and suppression between the five energy elements. Results: 10 constitutional types were derived. They had the highest vitality and stability, and they had permanent continuity, never changing their order of imbalanced structure. Conclusions: 10 constitutional types are logical and most reasonable when we classify the body types based on imbalanced structure of five energy elements.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1787-1793
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• 2018

The power conversion efficiency of perovskite solar cells has reached 23.3%. Although significant developments have been made through intensive studies, the stability issue is still challenging. Passivation of perovskite solar cells with a transparent polymer provides better stability; however, there are a few disadvantages of organic polymer such as low thermal stability, weak adhesion and the lack of water retention ability. In this work, we prepared a dual Parylene-F/C layer with 3-methacryloxypropyltrimethoxysilane, A-174, to combine the advantages of organic and inorganic materials. As a result, A-174 treated dual Parylene-F/C layer demonstrated improved passivation effects compared to a single Parylene layer due to the strong binding of Parylene and the water retention ability by $SiO_2$ formed from A-174. This synergetic effects can be expanded to the combination of other organic materials and organosilane compounds.

• Current Photovoltaic Research
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• v.9 no.4
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• pp.145-159
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• 2021

Light soaking (LS) stability in polymer solar cells (PSCs) has always been a challenge to achieve due to unstable photoactive layer-electrode interface. Especially, the electron transport layer (ETL) and photoactive layer interface limits the LS stability of PSCs. Herein, we have modified the most commonly used and robust zinc oxide (ZnO) ETL-interface using an organic dye molecule and a co-adsorbent. Power conversion efficiencies have been slightly improved but when these PSCs were subjected to long term LS stability chamber, equipped with heat and humidity (45℃ and 85% relative humidity), an outstanding stability in the case of ZnO/dye+co-adsorbent ETL containing devices have been achieved. The enhanced LS stability occurred due to the suppressed interfacial defects and robust contact between the ZnO and photoactive layer. Current density as well as fill factors have been retained after LS with the modified ETL as compared to un-modified ETL, owing to their higher charge collection efficiencies which originated from higher electron mobilities. Moreover, the existence of less traps (as observed from light intensity-open circuit voltage measurements and dark currents at -2V) are also found to be one of the reasons for enhanced LS stability in the current study. We conclude that the mitigation ETL-surface traps using an organic dye with a co-adsorbent is an effective and robust approach to enhance the LS stability in PSCs.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.10
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• pp.1175-1182
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• 1999

This paper shows that a well-defined energy function can be developed to reflect the transfer conductances for multi-machine power systems under an assumption that all transmission lines have uniform R/X rations. The energy function is derived by introducing a pure reactive equivalent system for the given system. In this study, a static energy function reflecting transfer conductances is also derived as well as the transient energy function. The proposed static energy function is applied to voltage stability analysis and tested for various sample systems. The test results show that the accuracy of voltage stability analysis can be considerable improved by reflecting transfer conductances into the energy function.

• Journal of Electrical Engineering and Technology
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• v.8 no.3
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• pp.478-489
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• 2013

The controllability and stability of power systems can be increased by Flexible AC Transmission Devices (FACTs). One of the FACTs devices is Interline Power-Flow Controller (IPFC) by which the voltage stability, dynamic stability and transient stability of power systems can be improved. In the present paper, the convenient operation and control of IPFC for transient stability improvement are considered. Considering that the system's Lyapunov energy function is a relevant tool to study the stability affair. IPFC energy function optimization has been used in order to access the maximum of transient stability margin. In order to control IPFC, a Brain Emotional Learning Based Intelligent Controller (BELBIC) and PI controller have been used. The utilization of the new controller is based on the emotion-processing mechanism in the brain and is essentially an action selection, which is based on sensory inputs and emotional cues. This intelligent control is based on the limbic system of the mammalian brain. Simulation confirms the ability of BELBIC controller compared with conventional PI controller. The designing results have been studied by the simulation of a single-machine system with infinite bus (SMIB) and another standard 9-buses system (Anderson and Fouad, 1977).

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1566-1577
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• 2018

This paper presents a stability analysis of AC-DC power system feeding a speed controlled DC motor in which this load behaves as a constant power load (CPL). A CPL can significantly degrade power system stability margin. Hence, the stability analysis is very important. The DQ and generalized state-space averaging methods are used to derive the mathematical model suitable for stability issues. The paper analyzes the stability of power systems for both speed control natural frequency and DC-link parameter variations and takes into account controlled speed motor dynamics. However, accurate DC-link filter and DC motor parameters are very important for the stability study of practical systems. According to the measurement errors and a large variation in a DC-link capacitor value, the system identification is needed to provide the accurate parameters. Therefore, the paper also presents the identification of system parameters using the adaptive Tabu search technique. The stability margins can be then predicted via the eigenvalue theorem with the resulting dynamic model. The intensive time-domain simulations and experimental results are used to support the theoretical results.

• Environmental and Resource Economics Review
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• v.32 no.2
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• pp.77-105
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• 2023

This paper investigates the management stability of KOSPI-listed energy public enterprises from the perspective of median voter theory. We analyze the profitability and stability of five energy public enterprises during the period 2011~2022, and conduct an empirical analysis to determine whether they are related to the preferences of median voters who can represent the general public. Our analysis of the profitability and stability of the energy public enterprises shows that the stability of their has been deteriorating in recent years. The results of the empirical analysis also show that the management stability of the energy public enterprises is related to the preference of median voter. Specifically, they indicate that when the median voter's income is smaller than the average income, the profitability of the utility decreases and the debt ratio increases. This paper suggests that from the median voter's point of view, excessive utility and energy bills may strengthen the incentives for governments and politicians to suppress rate increases, leading to lower profitability and higher debt for public enterprises.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.4
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• pp.1866-1888
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• 2017

Efficient energy consumption in WSN is one of the key design issues for improving network stability period. In this paper, we propose a new Heterogeneity-aware Energy-efficient Clustering (HEC) technique which considers two types of heterogeneity - network lifetime and of sensor nodes. Selection of cluster head nodes is done based on the three network lifetime phases: only advanced nodes are allowed to become cluster heads in the initial phase; in the second active phase all nodes are allowed to participate in cluster head selection process with equal probability, and in the last dying out phase, clustering is relaxed by allowing direct transmission. Simulation-based performance analysis of the proposed technique as compared to other relevant techniques shows that HEC achieves longer stable region, improved throughput, and better energy dissipation owing to judicious consumption of additional energy of advanced nodes. On an average, the improvement observed for stability period over LEACH, SEP, FAIR and HEC- with SEP protocols is around 65%, 30%, 15% and 17% respectively. Further, the scalability of proposed technique is tested by varying the field size and number of sensing nodes. The results obtained are found to be quite optimistic. The impact of energy heterogeneity has also been assessed and it is found to improve the stability period though only upto a certain extent.