• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.6
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• pp.503-510
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• 2020

The importance of DC breakers as key protection equipment is increasing in accordance with growing concerns on MVDC distribution network systems without DC/AC conversion. Different from the situation in AC systems, no natural zero-crossing point exists in DC systems. Thus, DC breaker technology is more difficult than AC breaker technology. The solutions for DC breakers can be divided into three types: mechanical, power electronics, and hybrid. In this study, the operating principles of several topologies of hybrid circuit breakers and that of the proposed DC breaker are analyzed and simulated by sorting two types. The breakers are compared in terms of the type and number of semiconductors, volume, power loss, auxiliary components, isolation, and other aspects. The advantages and disadvantages of the breakers are also analyzed.

• Journal of Distribution Science
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• v.8 no.2
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• pp.13-22
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• 2010

Customer Relationship Management(CRM) paradigm has emerged that suggests organizations will be more successfully if they concentrate on obtaining and maintaining a share of each customer rather than a share of the entire market, with information technology(IT) being the enabling factor. This paper presents five key elements that provide the necessary steps that allow and organization to position its people, business process, and information system to establish and take advantage of this paradigm. The key elements are : (1) IT investment, (2) Website application, (3) IT System application, (4) Communication strategies, (5) CRM Performance. The results show that IT investment, IT system application, and Website application play a vital role in enhancing an Organizational Communication. Also, the results show that IT investment, IT system application, Website application, and Organizational Communication play a vital role in enhancing an organization's performance of customer relationship management. Further, this paper discusses the importance of integrating these four elements for achieving effective customer interaction. The author provides academical and managerial implication for business strategies.

• Journal of Satellite, Information and Communications
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• v.12 no.1
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• pp.38-42
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• 2017

This paper introduces the concept of a dual hash function to amplify security in a quantum key distribution system. We show the use of the relationship between quantum error correction and security to provide security amplification. Also, in terms of security amplification, the approach shows that phase error correction offers better security. We describe the process of enhancing security using the universal hash function using the BB84 protocol, which is a typical example of QKD. Finally, the deterministic universal hash function induces the security to be evaluated in the quantum Pauli channel without depending on the length of the message.

• Convergence Security Journal
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• v.21 no.3
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• pp.3-11
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• 2021

Most of the internet security protocols rely on classical algorithms based on the mathematical complexity of the integer factorization problem, which becomes vulnerable to a quantum computer. Recent progresses of quantum computing technologies have highlighted the need for applying quantum key distribution (QKD) on existing network protocols. We report the development and integration of a plug & play QKD device with a commercial IPSec device by replacing the session keys used in IPSec protocol with the quantum ones. We expect that this work paves the way for enhancing security of the star-type networks by implementing QKD with the end-to-end IP communication.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.24 no.65
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• pp.81-88
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• 2001

In logistics decision making, Key elements in the design of any physical distribution are the location of depots and the distribution of goods from the depots to the customers. Considering open and close the depots, This paper presents a flexible analysis on the combined location-routing problem(LRP) the case for variation capacity of vehicle and customers demands each. The scenario examples are given the use of heuristic(Saving-Drop) in LRP types. The results is useful in apply to the logistics environment changes.

• Journal of Electrical Engineering and Technology
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• v.13 no.3
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• pp.1079-1088
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• 2018

A line overload emergency control strategy based on the source-load synergy coefficient is proposed in this paper. First, the definition of the source-load synergy coefficient is introduced. When line overload is detected, the source-load branch synergy coefficient and source-load distribution synergy coefficient are calculated according to the real-time operation mode of the system. Second, the generator tripping and load shedding control node set is determined according to the source-load branch synergy coefficient. And then, according to the line overload condition, the control quantity of each control node is determined using the Double Fitness Particle Swarm Optimization (DFPSO), with minimum system economic loss as the objective function. Thus load shedding for the overloaded line could be realized. On this basis, in order to guarantee continuous and reliable power supply, on the condition that no new line overload is caused, some of the untripped generators are selected according to the source-load distribution synergy coefficient to increase power output. Thus power supply could be restored to some of the shedded loads, and the economic loss caused by emergency control could be minimized. Simulation tests on the IEEE 10-machine 39-bus system verify the effectiveness and feasibility of the proposed strategy.

• Journal of Communications and Networks
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• v.18 no.5
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• pp.688-698
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• 2016

In this paper, we investigate the achievable sum rate and energy efficiency of downlink massive multiple-input multiple-output antenna systems with zero-forcing precoding, by taking into account the randomness of user locations. Specifically, we propose two types of non-uniform user distributions, namely, center-intensive user distribution and edge-intensive user distribution. Based on these user distributions, we derive novel tight lower and upper bounds on the average sum rate. In addition, the impact of user distributions on the optimal number of users maximizing the sum rate is characterized. Moreover, by adopting a realistic power consumption model which accounts for the transmit power, circuit power and signal processing power, the energy efficiency of the system is studied. In particular, closed-form solutions for the key system parameters, such as the number of antennas and the optimal transmit signal-to-noise ratio maximizing the energy efficiency, are obtained. The findings of the paper suggest that user distribution has a significant impact on the system performance: for instance, the highest average sum rate is achieved with the center-intensive user distribution, while the lowest average sum rate is obtained with the edge-intensive user distribution. Also, more users can be served with the center-intensive user distribution.

• Proceedings of the Korea Society for Simulation Conference
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• 1998.03a
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• pp.101-105
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• 1998

A large system predictor, which can perform prediction of sales trend in a huge number of distribution centers, is presented using neural predictive model. There are 20,000 number of distribution centers, and each distribution center need to forecast future demand in order to establish a reasonable inventory policy. Therefore, the number of forecasting models corresponds to the number of distribution centers, which is not possible to estimate that kind of huge number of accurate models in ERP (Enterprise Resource Planning)module. Multilayer neural net as universal approximation is employed for fitting the prediction model. In order to improve prediction accuracy, a sequential simulation procedure is performed to get appropriate network structure and also to improve forecasting accuracy. The proposed simulation procedure includes neural structure identification and virtual predictive model generation. The predictive model generation consists of generating virtual signals and estimating predictive model. The virtual predictive model plays a key role in tuning the real model by absorbing the real model errors. The complement approach, based on real and virtual model, could forecast the future demands of various distribution centers.

• Journal of the Korea Safety Management & Science
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• v.10 no.1
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• pp.139-144
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• 2008

Recently, a multi-facility, multi-product and multi-period industrial production-distribution planning problem has been widely investigated in Supply Chain Management (SCM). One of the key issues in the current SCM research area involves reducing both production and distribution costs. We have developed an optimization model to tackle the above problems under the restricted conditions such as transportation time and a zero inventory. Computational experiments using commercial tool Ms-Excel Solver show that the real size problems we encountered can be solved in reasonable time. The model can be used to decide an appropriate production-distribution planning problem in SCM research area.

• Journal of Power Electronics
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• v.16 no.2
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• pp.685-694
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• 2016

This paper presents a reliability assessment model for the power semiconductors used in wind turbine power converters. In this study, the thermal loadings at different timescales of wind speed are considered. First, in order to address the influence of long-term thermal cycling caused by variations in wind speed, the power converter operation state is partitioned into different phases in terms of average wind speed and wind turbulence. Therefore, the contributions can be considered separately. Then, in regards to the reliability assessment caused by short-term thermal cycling, the wind profile is converted to a wind speed distribution, and the contribution of different wind speeds to the final failure rate is accumulated. Finally, the reliability of an actual power converter semiconductor for a 2.5 MW wind turbine is assessed, and the failure rates induced by different timescale thermal behavior patterns are compared. The effects of various parameters such as cut-in, rated, cut-out wind speed on the failure rate of power devices are also analyzed based on the proposed model.