• The Transactions of The Korean Institute of Electrical Engineers
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• 제64권6호
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• pp.864-871
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• 2015

Recently, one of the main research on the power distribution system is the microgrid. The microgrid is a combination of power sources and loads, which is controllable and has separable connection. The main objective of microgrid is the deployment of the renewable clean energy and the enhancement of load-side reliability. The modern power sources and loads have DC I/O interfaces, which is the major advantage of DC microgrid compared to the conventional AC grid. The components in the microgrid have diverse features, so there is need of proper coordination control. For achieving economic feature, the active power of renewable energy resources is regarded as major control parameter and the whole operation modes of DC microgrid are defined, and the proper operations of each component are described. From the inherent characteristics of DC, there are two control variables: voltage and active power. Through analysis of operation modes, it is possible to determine exact control objectives and optimized voltage & power control strategy in each mode. Because of consideration of whole operation modes, regardless of the number and capacity of components, this coordination control method can be used without modification. This paper defines operation mode of DC microgrid with several DC sources and suggests economic and efficient coordinated control methods. Simulation with PSCAD proves effectiveness.

• Journal of Power Electronics
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• 제11권4호
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• pp.533-541
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• 2011

The redundant operation of a parallel AC to DC converter via a serial communication bus is presented. The proposed system consists of three isolated CUK power factor correction modules. The controller for each converter is a dsPIC30F6010 microcontroller while a RS485 communication bus and the clock signal are used for synchronizing the data communication. The control strategy of the redundant operation relies on the communication of information among each of the modules, which communicate via a RS485 serial bus. This information is received from the communication checks of the converter module connected to the system to share the load current. Performance evaluations were conducted through experimentation on a three-module parallel-connected prototype, with a 578W load and a -48V dc output voltage. The proposed system has achieved the following: the current sharing is quite good, both the transient response and the steady state. The converter modules can perform the current sharing immediately, when a fault is found in another converter module. In addition, the transient response occurs in the system, and the output voltages are at their minimum overshoot and undershoot. Finally, the proposed system has a relatively simple implementation for the redundant operation.

• Nuclear Engineering and Technology
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• 제54권8호
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• pp.2840-2851
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• 2022

Electric boilers (EBs) are the backup steam source for the auxiliary steam system of high-temperature gas-cooled reactor nuclear power plants. When the plant is in normal operations, the EB is always in hot standby status. However, the current hot standby operation strategy has problems of slow response, high power consumption, and long operation time. To solve these problems, this study focuses on the optimization of hot standby operations for the EB system. First, mathematical models of an electrode immersion EB and its accompanying deaerator were established. Then, a control simulation platform of the EB system was developed in MATLAB/Simulink implementing the established mathematical models and corresponding control systems. Finally, two optimization strategies for the EB hot standby operation were proposed, followed by dynamic simulations of the EB system transient from hot standby to normal operations. The results indicate that the proposed optimization strategies can significantly speed up the transient response of the EB system from hot standby to normal operations and reduce the power consumption in hot standby operations, improving the dynamic performance and economy of the system.

• Journal of Distribution Science
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• 제20권9호
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• pp.11-21
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• 2022

Purpose: Many concerns have appeared in banking sector in the digital era and one of them is that technology development will increase operation costs of banks. Motivated by this issue, our study aims to explore the effect of technological and digital investments on cost-effectiveness of banking operation. Research design, data and methodology: To reach a clear answer, we use the data of 12 commercial banks spanning from 2011 to 2020 in Vietnam and employ multivariate regression analysis as well as perform various robustness tests. Results: Our regression result indicates that the adverse effect of technological spending on cost-effective operation. This finding still remains unchanged when we conduct different robust tests. Also, we find that this negative impact becomes more evident in large banks than in small ones. Conclusions: The paper provides one of the most important empirical results for mangers and policy-makers in banking sphere, especially in Vietnam where regulators have been calling for continuously investing into technological innovation in banks. The evidence confirms that banks should carefully consider an increase in spending on distribution information and communication technologies when constructing business strategies related to expanding digitalization. Our research is also useful for countries having similar financial structure to Vietnam.

• Journal of Korean Society of Transportation
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• 제33권3호
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• pp.237-246
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• 2015

Operation and Maintenance in road infrastructure is repetitive carbon emissions activities to preserve the road in its originally constructed condition. In the view of road planning and construction, operation, and maintenance of life cycle, operation and maintenance stage quantification of carbon emissions is very important because it is easily accessible activities to reduce carbon emissions in road infrastructure that existing and new road. However, carbon emissions estimation in operation and maintenance stage is yet to do, because data collection is so hard and carbon emissions estimation methodology is very complicated. In this study, a basic unit of carbon emission in the operation and maintenance stage of the road infrastructure was developed in order to get the quantitative determination of carbon that occurring. Carbon emissions of the Expressway and Common state road was calculated by using the basic unit of carbon emission and application plan of basic unit of carbon emission are presented.

• Journal of Intelligence and Information Systems
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• 제21권1호
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• pp.47-63
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• 2015

As knowledge is paid attention as a new production factor that generates added value, studies continue to apply knowledge management to business environment. In addition, as ICT (Information Communication Technology) was engrafted in business environment, it leads to increasing task efficiency and productivity of individual workers. Accordingly, the way that a business achieves its goal has changed to one in which its individual members are willing to take part in the organization and share information to create new values (Han, 2003) and studies for the system and service to support such transition are carrying out. Of late, a new concept called 'Enterprise 2.0' newly appears. It is the extension of Wen 2.0 and its technology, which focus on participation, sharing and openness, to the work environment of a business (Jung, 2013). Enterprise 2.0 is being used as a collaborative tool to prop up individual creativity and group brain power by combining Web 2.0 technologies such as blog, Wiki, RSS and tag with business software (McAfee, 2006). As Tweeter gets popular, Enterprise Microblog (EMB), which is an example of Enterprise 2.0 for business, has been developed as equivalent to Tweeter in business circle and SaaS (Software as a Service) such as Yammer was introduced The studies of EMB mainly focus on demonstrating its usability in terms of intra-firm communication and knowledge management. However existing studies lean too much towards large-sized companies and certain departments, rather than a company as a whole. Therefore, few studies have been conducted on small and medium-sized companies that have difficulty preparing separate resources and supplying exclusive workforce to introduce knowledge management. In this respect, the present study placed its analytic focus on small-sized companies actually equipped with EMB to know how they use it. And, based on the findings, this study examined their knowledge management strategies for EMB from the point of codification and personalization. Hypothesis -"as a company grows, it shifts EMB strategy from codification to personalization'- was established on the basis of reviewing precedent studies and literature. To demonstrate the hypothesis, this study analyzed the usage of EMB by small companies that have used it from foundation. For case study, the duration of the use was divided into 2 spans and longitudinal analysis was employed to examine the contents of the blogs. Using the key findings of the analysis, this study is aimed to propose practical implications for the operation of knowledge management of small-sized company and the suitable application of knowledge management system for operation Knowledge Management Strategy can be classified by codification strategy and personalization strategy (Hansen et. al., 1999), and how to manage the two strategies were always studied. Also, current studies regarding the knowledge management strategy were targeted mostly for major companies, resulting in lack of studies in how it can be applied on SMEs. This research, with the knowledge management strategy suited for SMEs, sets an Enterprise Microblog (EMB), and with the EMB applied on SMEs' Knowledge Management Strategy, it is reviewed on the perspective of SMEs' Codification and Personalization Strategies. Through the advanced research regarding Knowledge Management Strategy and EMB, the hypothesis is set that "Depending on the development of the company, the main application of EMB alters from Codification Strategy to Personalization Strategy". To check the hypothesis, SME that have used the EMB called 'Yammer' was analyzed from the date of their foundation until today. The case study has implemented longitudinal analysis which divides the period when the EMBs were used into three stages and analyzes the contents. As the result of the study, this suggests a substantial implication regarding the application of Knowledge Management Strategy and its Knowledge Management System that is suitable for SME.

• Journal of Korean Society for Quality Management
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• 제46권4호
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• pp.899-910
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• 2018

Purpose: Generally, since the population density is lower in suburban areas, the distance to school is inevitably long. Therefore, schools in suburban areas often operate school buses to improve student welfare. However, since school buses are usually used only during going to and from school, the utilization rates are relatively low. Therefore, this study aims to establish integrated operation plan of public school bus covering all schools. Methods: It is necessary to decide which school buses will serve the specific demand node which want to go to certain school in order to design an integrated operation plan for school buses. Therefore, a mathematical model is developed for minimizing the total number of vehicles and the distance of transportation by reflecting the characteristics of school buses and students as constraints. To solve the proposed mathematical model, CPLEX, a commercial solver, is applied. Results: To validate and to confirm the proposed process, numerical example is designed with the comparison between before and after integrated operations of school buses in terms of total operation cost. The result shows that the integrated operation can lead the reduction of the number of school buses as well as the decreasing of the fuel cost. Conclusion: This study provides the quantitative method to perform the integrated operation of school buses in suburban areas. The optimal operation strategy is required because there are more complex decision-making elements considering the integrated operation. It is expected to apply this research result at real situation to expand this services based on an optimal operation.

• Strategy21
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• 통권34호
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• pp.178-206
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• 2014

The battlefield environment in the maritime has been changed by advanced IT technology, variation of naval warfare condition, and developed military science and technology. In addition, state-of-the-art surface combatants has become to multi-purpose battleship that is heavily armed in order to meet actively in composed future sea battlefield condition and perform multi-purpose missions as well as having capability of strategic strike. To maximize the combat strength and survivability of ship, it is not only possible for Zumwalt(DDG-1000) class combatant to conduct multi-purpose mission with advanced weapon system installation, innovative hull form and upper structure such as deckhouse, shipboard high-powered sensor, total ship computing environment, and integrated power control but it was designed so that can be installed with energy based weapon systems in immediate future. Zumwalt class combatant has been set a high value with enormous threatening surface battleship in the present, it seems to be expected that this ship will be restraint means during operation in the littoral. The advent of Zumwalt class battleship in the US Navy can be constructed as a powerful intention of naval strength building for preparing future warfare. It is required surface ship that can be perform multi-purpose mission when the trend of constructed surface combatants was analyzed. In addition, shipboard system has been continuously modernized to keep the optimized ship and maximize the survivability with high-powered detection and surveillance sensor as well as modularity of combat system to efficient operation.

• Journal of the Economic Geographical Society of Korea
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• 제14권2호
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• pp.157-175
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• 2011

This paper aims to analyze the characteristics of healthcare REITs' performance and operation, and to examine their use for activating the silver industries in Korea. The results of this study are as follows. First, according to the results of analyzing healthcare REITs' performance, healthcare REITs outperformed average REITs and extended investment proportion compared to total REITs after 2007. This outperforming came from not only rapid growth of silver industries, but also REITs strategy using the structure of sale-and-leaseback and triple-net lease. Second, healthcare REITs use selection and concentration strategy in terms of asset sector, but use portfolio diversification strategy in terms of investment region. Third, according to the analysis results, healthcare REITs are to be useful for activating the silver industries in Korea. In this context, major implications are presented to use healthcare REITs effectively.

• Journal of Power Electronics
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• 제18권5호
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• pp.1595-1607
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• 2018

In this paper, a hierarchical control strategy is introduced to control a new three-port multidirectional DC-DC converter for integrating an energy storage system (ESS) to a bipolar DC microgrid (BPDCMG). The proposed converter provides a voltage-balancing function for the BPDCMG and adjusts the states of charge (SoC) of the ESS. Previous studies tend to balance the voltage of the BPDCMG buses with active sources or by transferring power from one bus to another. Furthermore, the batteries available in BPDCMGs were charged equally by both buses. However, this power sharing method does not guarantee efficient operation of the whole system. In order to achieve a higher efficiency and lower energy losses, a triple-layer hierarchical control strategy, including a primary droop controller, a secondary voltage restoration controller and a tertiary optimization controller are proposed. Thanks to the multi-functional operation of the proposed converter, its conversion stages are reduced. Furthermore, the efficiency and weight of the system are both improved. Therefore, this converter has a significant capability to be used in portable BPDCMGs such as electric DC ships. The converter modes are analyzed and small-signal models of the converter are extracted. Comprehensive simulation studies are carried out and a BPDCMG laboratory setup is implemented in order to validate the effectiveness of the proposed converter and its hierarchical control strategy. Simulation and experimental results show that using the proposed converter mitigates voltage imbalances. As a result, the system efficiency is improved by using the hierarchical optimal power flow control.