• Journal of Power Electronics
• /
• v.11 no.4
• /
• pp.533-541
• /
• 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.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.22 no.4
• /
• pp.336-344
• /
• 2017

This paper presents the three-port DC-DC converter modeling and controller design procedure, which is part of the solid-state transformer (SST) to interface medium voltage AC grid to bipolar DC distribution network. Due to the high primary side DC link voltage, the proposed converter employs the three-level neutral point clamped (NPC) topology at the primary side and 2-two level half bridge circuits for each DC distribution network. For the proposed converter particular structure, this paper conducts modeling the three winding transformer and the power transfer between each port. A decoupling method is adopted to simplify the power transfer model. The voltage controller design procedure is presented. In addition, the output current sharing controller is employed for current balancing between the parallel-connected secondary output ports. The proposed circuit and controller performance are verified by experimental results using a 30 kW prototype SST system.

• Proceedings of the KIEE Conference
• /
• 2003.11a
• /
• pp.379-381
• /
• 2003

The sharing of common corridors by electric power transmission lines and pipelines is becoming more common place. However, such corridor sharing can result in undesired coupling of electromagnetic energy from the power lines to the near facilities. This causes induced voltages on underground metallic pipelines due to the power line currents. This could cause AC corrosion in the pipeline, which could in turn lead to disastrous accidents, such as gas explosion or oil leakage. This paper investigates for the limitation of induced voltage on the buried metal structures which is used in the inside and outside of the country. And then we measure the earth resistance and leakage current of 22.9kV distribution lines and pipe to soil potential of near pipelines in Seoul Korea. Hereby we can see the leakage current flowing through the earthing electrode have an effect on near pipelines.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.19 no.1
• /
• pp.15-22
• /
• 2014

Recently, parallel operation of dc-dc converters has been widely used in distributed power systems. In this paper, a control method to achieve parallel operation of three-phase bi-directional isolated interleaved dc-dc converters is discussed for the battery charging and discharging system which consists of the 32 battery charger/dischargers and two three-phase bi-directional isolated interleaved dc-dc converters. In the boost mode, the battery energy is delivered to the grid, whereas the grid energy is transferred to the battery in the buck mode operation. The average current sharing control method is employed to obtain an equal conducting of each phase current in the three-phase dc-dc converter. By using the proposed method, the imbalance factor is gratefully reduced from 8 percent to 1 percent. Two 2.5kW three-phase bi-directional dc-dc converter prototype have been built and the proposed method has been verified through experiments.

• Asia pacific journal of information systems
• /
• v.29 no.3
• /
• pp.359-381
• /
• 2019

Social networking services (SNSs) have become important and popular tools for not only presenting self-image but also sharing travel information. This study adopted self-image expressions to understand tourists' intentions to share travel information and behavioral changes in SNSs. To enhance understanding tourists' intention and behavior, the current study suggests a research model based on motivations for self-image expression (i.e., creativity, altruism and social relationship). This current study empirically resulted in the importance of users' creativity, altruism and social relationship in SNS, which leads to the intention and behavioral changes to share travel information. In addition, altruism moderated the negative effect of creativity on self-image expression as well as the positive effect of the social relationship on self-image expression. Based on the result of this study, the current study bears some implications in a theoretical and practical context.

• Journal of the Korean BIBLIA Society for library and Information Science
• /
• v.33 no.1
• /
• pp.47-70
• /
• 2022

The purpose of this study is to empirically verify the factors(organization managerial factors, relational factors and personal factors) that affect the knowledge sharing intention of records management specialists. A total of 126 responses were used for the final analysis and the findings of this study are as follows: First, managers' interests and supports had a significant positive effect on tacit knowledge sharing intention, but evaluation and compensation system had a negative effect on tacit knowledge sharing intention. Second, job stress was found to have a significant positive effect on the intention of knowledge sharing(tacit, explicit). It is required to form an organizational culture where records management specialists can freely participate in knowledge sharing activities with the interest and support of managers. In addition, the process of continuously improving the causes of one of the causes of job stress, such as awareness improvement and deprivation, should be carried out through records management training for all employees. This study is meaningful in that it provides policy implications for promoting knowledge sharing as a solution to the managerial problems faced by records management specialists by utilizing the current staffing structure.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.29 no.4
• /
• pp.116-125
• /
• 2015

This paper presents experimental results obtained from actual installation conditions of surge protective devices (SPDs), with the aim of understanding the coordination of cascaded Class I and Class II SPDs. This paper also proposes effective methods for selecting and installing coordinating cascaded SPDs. The residual voltage of each SPD and the energy sharing of an upstream Class I tested SPD and a downstream Class II tested SPD were measured using a $10/350{\mu}s$ current wave. In coordinating a cascaded voltage-limiting SPD system, it was found that energy coordination can be achieved as long as the downstream SPD is a metal oxide varistor with a higher maximum continuous operating voltage than the upstream SPD; however, it is not the optimal condition for the voltage protection level. If the varistor voltage of the downstream SPD is equal to or lower than that of the upstream SPD, the precise voltage protection level is obtained. However, this may cause serious problems with regard to energy sharing. The coordination for energy sharing and voltage protection level is fairly achieved when the cascaded SPD system consists of two voltage-limiting SPDs separated by 3 m and with the same varistor voltage.

• Journal of The Korean Association of Information Education
• /
• v.10 no.2
• /
• pp.273-280
• /
• 2006

Most homepages of schools are available to publicize activities of education, to load educational materials efficiently. But we can't use current homepages of schools in making characteristic information or sharing educational resources. In this study, this CUBE system with RSS and mobile phone was designed and embodied for sharing characteristic educational activities and works in schools. Currently, CUBE is being under experimental test in elementry schools at Sancheong area, and instructors and students are operating CUBE for sharing education activities and making community in this system,.

• Journal of Society of Preventive Korean Medicine
• /
• v.10 no.2
• /
• pp.95-120
• /
• 2006

The purpose of this paper is to investigate the structure of cost-sharing for oriental medical services in the national health insurance. Out-of-pocket payment in ambulatory oriental medical care is a co-payment of KRW3,000 up to total expenses of KRW15,000, and co-insurance rate of 30% thereafetr. The empirical analysis based on medial claims data shows that the frequency of medical claims for outpatient care are mostly concentrated just below a total expenses of KRW15,000, and it decreases beyond a total expense of KRW15,000, while it rebounds between KRW17,000${\sim}$20,000. This means the current co-payment(KRW3,000) in oriental medical services should be applied up to a total payment of KRW17,000${\sim}$20,000, or the level of co-payment should be adjusted upward to KRW45,000 in order to be consistent in cost-sharing, between co-payment and co-insurance.

• 한국정보통신설비학회:학술대회논문집
• /
• 2007.08a
• /
• pp.390-393
• /
• 2007

The reliability as well as the power capability of the UPS system can be increased by replacing a single UPS unit with multiple small UPS units in parallel, resulting in a so-called module UPS. This module UPS system allows that a new module can be added or replaced while maintaining power to loads, which is a hot-swappable operation. In addition, it has desirable features such as ease of output power expandability, convenience of maintenance and repair, and high reliability. To realize the module UPS, load sharing without interconnection among parallel connecting modules as well as a small scale and lightweight topology is necessary. The frequency and voltage droop method is applied to parallel operation control to achieve load sharing. 5kVA modules are designed and implemented to confirm the effectiveness of the proposed approaches. Experimental results show that the module UPS system has a high power factor, a low distortion of output voltage and input current, hot-swappable operations and good load sharing characteristics.