Korea Electrical Engineering and Science Research Institute

Seoul, South Korea

Korea Electrical Engineering and Science Research Institute

Seoul, South Korea
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Choi S.H.,Korea Electrical Engineering and Science Research Institute | Shim H.J.,Seoul National University
Annals of Nuclear Energy | Year: 2016

The current Monte Carlo (MC) adjoint-weighted tally techniques based on the iterated fission probability (IFP) concept require a memory amount which is proportional to the numbers of the adjoint-weighted tallies and histories per cycle to store history-wise tally estimates during the convergence of the adjoint flux. Especially the conventional MC adjoint-weighted perturbation (AWP) calculations for the nuclear data sensitivity and uncertainty (S/U) analysis suffer from the huge memory consumption to realize the IFP concept. In order to reduce the memory requirement drastically, we present a new adjoint estimation method in which the memory usage is irrelevant to the numbers of histories per cycle by applying the IFP concept for the MC Wielandt calculations. The new algorithms for the adjoint-weighted kinetics parameter estimation and the AWP calculations in the MC Wielandt method are implemented in a Seoul National University MC code, McCARD and its validity is demonstrated in critical facility problems. From the comparison of the nuclear data S/U analyses, it is demonstrated that the memory amounts to store the sensitivity estimates in the proposed method become negligibly small. © 2016 Elsevier Ltd.


Park G.-P.,Seoul National University | Heo J.-H.,Korea Electrical Engineering and Science Research Institute | Lee S.-S.,Korea Electrical Engineering and Science Research Institute | Yoon Y.T.,Korea Electrical Engineering and Science Research Institute
Journal of Electrical Engineering and Technology | Year: 2011

The purpose of power system maintenance is to prevent equipment failure. The maintenance strategy should be designed to balance costs and benefits because frequent maintenance increases cost while infrequent maintenance can also be costly due to electricity outages. This paper proposes maintenance modeling of a power distribution system using reliability centered maintenance (RCM). The proposed method includes comprehensive equipment modeling and impact analysis to evaluate the effect of equipment faults. The problem of finding the optimum maintenance strategy is formulated in terms of dynamic programming. The applied power system is based on the RBTS Bus 2 model, and the results demonstrate the potential for designing a maintenance strategy using the proposed model.


Heo J.-H.,Seoul National University | Kim M.-K.,Dong - A University | Park G.-P.,Seoul National University | Yoon Y.T.,Seoul National University | And 3 more authors.
IEEE Transactions on Power Delivery | Year: 2011

Electric power transmission utilities try to maximize profit by reducing electricity supply costs and operation costs while maintaining their reliability. Developing maintenance strategies is one of the effective ways to achieve these profitable goals. The reliability-centered maintenance approach is a key method in providing optimal maintenance strategies. It considers the tradeoffs between the upfront maintenance costs and the potential costs of reliability losses. Since a transmission system is a group of different kinds of equipment and the reliability of the electric facilities varies with time, an equipment state model using a modified semi-Markov chain is proposed. In addition, a genetic algorithm is used to find the optimal maintenance strategies from a large class of possible maintenance scenarios. These optimal maintenance strategies have been tested on an IEEE 9-bus system and an IEEE 118-bus system; the results show that the proposed method minimizes the total expected costs. © 2011 IEEE.


Yi S.-K.,Korea Electrical Engineering and Science Research Institute | Sin H.-Y.,Seoul National University | Heo E.,Seoul National University
Renewable and Sustainable Energy Reviews | Year: 2011

Renewable energy (RE) is the best sustainable energy solution South Korea can provide to assist North Korea in overcoming its chronic energy shortage. Designed as a follow-on research to Sin et al. [1], a survey was conducted with a panel of experts consisting of various disciplines and affiliations using the analytic hierarchy process (AHP) with benefit, opportunity, cost, and risk (BOCR). The results showed the panel viewed security as the most important factor among the strategic criteria. For the level 1 attributes, the panel showed no significant differences of opinion among the different alternatives; however, cost showed to be the most important factor for the panel. The panel chose wind power as the best alternative source of energy for North Korea; however, there were some differences in opinion among the sub-groups of the panel depending on the composition and the expertise of the sub-group. Compared to other studies on the similar topic, this research stands out in that the research results were derived using AHP and BOCR and that the panel was composed of both Korean and foreign experts on North Korea affiliated with state-run research organizations, armed forces, non-governmental organizations, academic research organizations, private consulting firms, and journalism. The research arrived at the conclusion that the following factors must be considered as South Korea designs its future North Korean energy assistance policy: (1) RE assistance for North Korea can take on various forms; hence, experts consulted during the design, writing, and implementation phases of the policy in question must possess knowledge and expertise in the appropriate technology and methodology being considered; (2) possibility of a sudden destabilization of the Northeast Asian security paradigm due to the collapse of North Korea; and (3) continued nuclearization of North Korea. © 2010 Elsevier Ltd.


Hahn T.,Korea Electrical Engineering and Science Research Institute | Tan Z.,North China Electrical Power University | Ko W.,Gachon University
IEEE Transactions on Smart Grid | Year: 2013

Under fixed retail rates, electricity demands have no incentive to change their usage pattern. In contrast, under time-varying rates, suppliers can reflect the actual supply cost during the peak hours in retail prices enabling end-users to respond to the prices and reduce their loads or shift their loads from the high-price hours to the low-price hours. Load shifting may increase the reliability of the system, but may increase CO-2 emission if coal-fired generators are the marginal generator used during the low- price hours. CO-2 emission taxation is one of ISO's options to deal with the CO-2 emission problem. In this paper, a new time-varying rate design method considering the CO-2 emission taxation is suggested. In addition, market power problem and non-shifting elastic loads are considered. The suggested method is applied to a test market with critical peak pricing (CPP) and real-time pricing (RTP) and the results are analyzed. Also the suggested method is applied to the Korean power system and the results are analyzed. © 2012 IEEE.


Ko W.,Gachon University | Hahn T.-K.,Korea Electrical Engineering and Science Research Institute
IEEE Transactions on Smart Grid | Year: 2013

Due to the recent global trend toward stricter restrictions on both greenhouse gases emission and energy consumption, there is an emerging attention on electric vehicles (EVs). It is anticipated that proliferation of EV will be expanded rapidly in the near future. Accordingly, there is a need to analyze the consumer preferences for the EVs as the basic data for developing the relevant industries' strategies in the newly emerging market of EVs or establishing the government policies to popularize EVs. This paper analyzes the consumer preferences for the EV on the basis of the stated preference data from consumers in Korea. A conjoint method and a mixed logit model using the Bayesian approach were used to estimate the preferences of consumers. The stated preference data of the conjoint method is collected through a face-to-face survey conducted in June 2009. The consumer preferences on the key attributes that affect the choices of EV are estimated by a mixed logit model. Marginal willingness to pay is calculated to quantitatively analyze the consumer preferences on the key attributes. The results of this paper show that the consumers have greater preference for EV with swappable battery rather than unswappable battery, and for lump-sum payment rather than installment of the subsidies. © 2012 IEEE.


Na J.H.,Korea Electrical Engineering and Science Research Institute | Park M.S.,Korea Electrical Engineering and Science Research Institute | Choi J.Y.,Korea Electrical Engineering and Science Research Institute
Pattern Recognition | Year: 2010

In this paper, we propose a new discriminant analysis, called linear boundary discriminant analysis (LBDA), which increases class separability by reflecting the different significances of non-boundary and boundary patterns. This is achieved by defining two novel scatter matrices and solving the eigenproblem on the criterion described by these scatter matrices. As a result, the classification performance using the extracted features can be improved. This effectiveness of the LBDA is theoretically explained by reformulating the scatter matrices in pairwise form. Experiments are conducted to show the performance of LBDA, and the results show that LBDA can perform better than other algorithms in most cases. © 2009 Elsevier Ltd. All rights reserved.


Cho S.-C.,Korea Electrical Engineering and Science Research Institute | Lee B.-H.,Inha University
Transactions of the Korean Institute of Electrical Engineers | Year: 2016

The parameters of Debye's equation were applied to analyze the frequency-dependent ground impedance of horizontally-buried wires. We present a new method, based on Debye's equation, of analyzing the effect of polarization on frequency-dependent ground impedance. The frequency-dependent ground impedances of a horizontally-buried wire are directly measured and calculated by applying sinusoidal current in the frequency range of 100 Hz to 10 MHz. Also, the results obtained in this work were compared with the data calculated from empirical equations and commercial programs. A new methodology using the delta-gap source model is proposed in order to calculate frequency-dependent ground impedance when the ground current is injected at the middle-point of the horizontal ground electrode. The high frequency ground impedance of horizontal electrodes longer than 30 m is larger or equal to its low frequency ground resistance. Consequently, the frequency-dependent ground impedance simulated with the proposed method is in agreement with the experimental data, and the validity of the computational simulation approach is confirmed. Copyright © The Korean Institute of Electrical Engineers.


Patent
Korea Electrical Engineering, Science Research Institute and LG Corp | Date: 2013-01-24

A three-level inverter having two direct current (DC)-links for converting DC voltages generated in a plurality of photovoltaic (PV) modules into alternating current (AC) voltages, wherein one end of a first DC-link of the two DC-links is connected to a first potential point at which a first potential is generated in the plurality of PV modules, and one end of a second DC-link of the two DC-links is connected to a second potential point at which a second potential that is lower than the first potential is generated in the plurality of PV modules, and both the other end of the first DC-link and the other end of the second DC-link are connected to a third potential point at which a third potential having a medium level between the first potential and the second potential is generated in the plurality of PV modules.


Patent
LG Corp, Korea Electrical Engineering and Science Research Institute | Date: 2014-04-16

A three-level inverter having two direct current (DC)-links for converting DC voltages generated in a plurality of photovoltaic (PV) modules into alternating current (AC) voltages, wherein one end of a first DC-link of the two DC-links is connected to a first potential point at which a first potential is generated in the plurality of PV modules, and one end of a second DC-link of the two DC-links is connected to a second potential point at which a second potential that is lower than the first potential is generated in the plurality of PV modules, and both the other end of the first DC-link and the other end of the second DC-link are connected to a third potential point at which a third potential having a medium level between the first potential and the second potential is generated in the plurality of PV module.

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