• 전력전자학회논문지
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• 제24권4호
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• pp.229-236
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• 2019

This study proposes a DC-DC converter topology of solid-state transformer for low-voltage DC distribution. The proposed topology consists of a voltage balancer and bipolar DC-DC converter. The voltage and current equations are obtained on the basis of switching states to design the controller. The open-loop gain of the controller is achieved using the derived voltage and current equations. The controller gain is selected through the frequency analysis of the loop gain. The inductance and capacitance are calculated considering the voltage and current ripples. The prototype is fabricated in accordance with the designed system parameters. The proposed topology and designed controller are verified through simulation and experiment.

• 대한전기학회논문지:전력기술부문A
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• 제51권7호
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• pp.349-361
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• 2002

Occasionally, equipment in a distribution system fails due to damage from weather, vandalism, or other causes. Failures and unexpected events do not always occur as and where expected. Therefore, a good contingency plan, multi-zone or otherwise, provides flexibility by locating switches at various strategic locations so that parts of a feeder can be picked up in the event of line outages at various places. It is possible to create feeder system layout that achieve remarkable contingency support economics, even as their normal peak loading levels approach thermal capacity, by utilizing six, seven, or even nine switchable zones per feeder. But many switchable zones per feeder are of questionable practicality and effectiveness, because of the complexity and time required for the switching operation. In practice, a zonal scheme with between three and four zones will usually provide complete contingency backup for all feeders. Line switches have both capital and maintenance costs, the planning for multi-zonal schemes is considerably more difficult than or loop or single-zone systems, and the required switching operations required during contingencies take more time. But multi-zonal schemes are used because these costs come to far less than the cost of additional capacity required for loop or single-zone. In this paper, we present the optimal number of switchable zones per feeder in Kora distribution system.

• Industrial Engineering and Management Systems
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• 제6권2호
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• pp.125-135
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• 2007

An automated guided vehicle (AGV) system is a group of collaborating unmanned vehicles which is commonly used for transporting materials within manufacturing, warehousing, or distribution systems. The performance of an AGV system depends on the dispatching rules used to assign vehicles to pickup requests, the vehicle routing protocols, and the home location of idle vehicles, which are called dwell points. In manufacturing and distribution environments which emphasize just-in-time principles, performance measures for material handling are based on response times for pickup requests and equipment utilization. In an AGV system, the response time for a pickup request is the time that it takes for the vehicle to travel from its dwell point to the pickup station. In this article, an exact dynamic programming algorithm for selecting dwell points in a tandem-loop multiple-vehicle AGV system is presented. The objective of the model is to minimize the maximum response time for all pickup requests in a given shift. The recursive algorithm considers time restrictions on the availability of vehicles during the shift.

• International Journal of Control, Automation, and Systems
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• 제5권6호
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• pp.607-613
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• 2007

Eigenstructure assignment provides the advantage of allowing great flexibility in shaping the closed-loop system responses by allowing specification of closed-loop eigenvalues and corresponding eigenvectors. But, the general eigenstructure assignment methodologies cannot guarantee stability robustness to parameter variations of a system. In this paper, we present a novel method that has the capability of exact assignment of an eigenstructure which can consider the probability of instability for LTI (Linear Time-Invariant) systems. The probability of instability of an LTI system is determined by the probability distributions of the closed-loop eigenvalues. The stability region for the system is made probabilistically based upon the Monte Carlo evaluations. The proposed control design method is applied to design a flight control system with probabilistic parameter variations to confirm the usefulness of the method.

• 한국화재소방학회논문지
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• 제29권1호
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• pp.73-79
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• 2015

스프링클러 설비의 설계방법은 크게 3가지로 분류한다. 가지관을 서로 연결하여 사다리형태로 배관을 설치하는 Grid형과 가지관은 연결하지 않고 교차배관만을 연결하는 Loop형 그리고 가장 일반적으로 사용되는 Tree형이 있다. 이 중 Grid형은 아주 간단한 것을 제외하고는 컴퓨터프로그램으로 마찰손실을 계산하여야 하지만 Loop형의 경우는 프로그램의 도움 없이 설계자가 직접 계산하여 마찰손실에 따른 필요압력과 소요유량을 산출할 수 있다. Loop형 설비의 경우 소화수 공급이 2방향으로 분리되어 마찰손실이 작아지고 헤드간 방출압력의 차이가 Tree형보다 작게 되어 살수분포가 우수하게 되며 작은 마찰손실에 의한 소구경의 배관을 사용하여 자재비와 인건비가 절감되므로 Loop형에 의한 스프링클러의 설계가 Tree형 설비에 비해 성능과 경제성에서 우수한 설계 방법이다. 하지만 Loop형 설비의 설계는 설계방법이 잘 알려져 있지 않아 거의 이루어지지 않고 있다. 본 논문에서는 Tree형 보다 우수한 Loop형 설비의 설계방법을 설명하여 많은 설계자가 성능과 경제면에서 우수한 Loop형 설계를 쉽게, 널리 사용하게 하고자 하였다.

• 조명전기설비학회논문지
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• 제27권9호
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• pp.83-89
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• 2013

Power distribution system has been changed from radial system to closed loop or mesh system due to connection of distributed generation growth. Data from distribution equipments which are installed at distribution line is required to be accurate for the performance of DMS(Distribution Management System). This paper analyzes the voltage measurement data from distribution equipment. However, the results of the analysis are confirmed to have some errors in voltage measurement data from distribution equipment. These errors come from aging of voltage sensor in distribution equipment and inaccurate data transfer to FRTU(feeder remote terminal unit) through the controller. The main problem is that the voltage measurement data of distribution equipment can not be assessed after it's first installation at the distribution line. The voltage measurement accuracy assessment system is to assess the voltage measurement data from distribution equipment on hot-line. This study had a field test to verify the performance of system.

• 전기학회논문지
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• 제58권3호
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• pp.431-436
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• 2009

As the telecommunication lines bring into widespread use, one of the most important aspects related to power distribution systems is effectively to evaluate the effect on the telecommunication lines from power lines. One of the efficient methods to evaluate the effect is to measure the induced voltage of a telecommunication line as a result of a ground-loop. If the power lines cause high induced voltage, the ground reference in the telecommunication lines is no longer a stable potential, so signals may ride on the noise. A ground loop is common wiring conditions where a ground current may take more than one path to return to the grounding electrode at the arrangement between the power lines and telecommunication lines. When a multi-path connection between the power lines and telecommunication line circuits exists, the resulting arrangement is known as a ground loop. Whenever a ground loop exists, there are potential for damages or abnormal operations of the telecommunication lines. The power lines can induce the voltage on the communication line. The effects can be calculated by considering the inductances and capacitances. However, if we assume that there are only power lines, it doesn't have a practical meaning because there are conductors with other purpose in the neighborhood of the lines. If we consider that case, we need more complex system. Therefore we suggest more complex system considering the conductors with other purpose in the neighborhood of the lines. The neutral wires and the overhead ground wires are considered for calculating the induced voltage. We assume that there are the messenger wires beside the power line as a result of increased use of them. The main purpose of this paper is a study on a shielding effect of messenger wires in the distribution lines. EMTP(Electro-Magnetic Transients Program) program is used for the induced voltage calculation.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.1638-1646
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• 2008

This paper presents a series of numerical simulations on the thermal performance and sectional efficiency of a closed-loop vertical ground heat exchanger (U-loop) equipped in a geothermal heat pump system (GHP). A 2-D finite element analysis, ANSYS, was employed to evaluate the temperature distribution on the borehole cross section involving HDPE pipe/grout/soil formation to compare the sectional efficiency between the conventional U-loop and a new latticed HDPE pipe system which is equipped with a thermally insulating latice in order to reduce thermal interference between the inflow and outflow pipes. In addition, a 3-D finite volume analysis (Fluent) was used to simulate the operating process of the closed-loop vertical ground heat exchanger by considering the effect of grout's thermal properties, rate of circulation pump, distance between the inflow and outflow pipes, and the effectiveness of the latticed HDPE pipe system. It was observed that the thermal interference between the two strands of U-loop is of importance in determining the efficiency of the ground heat exchanger, and thus it is highly recommendable to modify the cross section configuration of the conventional U-loop system by including a thermally insulating latice between the two strands.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.385-395
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• 2009

In this study, a series of numerical analysis has been accomplished on the thermal performance and sectional efficiency of a closed-loop vertical ground heat exchanger (U-loop) in a geothermal heat pump system (GHP) considering the circulating fluid, pipe, grout and soil formation. A finite element analysis program, ABAQUS, was employed to evaluate the temperature distribution on the cross section of the U-loop system involving HDPE pipe/grout/formation and to compare sectional efficiency between the conventional U-loop and a new latticed HDPE pipe system. Especially, the latticed pipe is equipped with a thermal insulation zone in order to reduce thermal interference between the inflow pipe and the outflow pipe. Also, a thermal stress analysis was performed with the aid of ABAQUS. 3-D finite volume analysis program, FLUENT, was adapted to analyze a coupled system between fluid circulation in the pipe and heat transfer and simulate an operating process of the closed-loop vertical ground heat exchanger. In this analysis, the effect of the thermal properties of grout, rate of circulation pump, distance between the inflow pipe and the outflow pipe, and the effectiveness of the latticed HDPE pipe system are taken into account.

• 천문학회보
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• 제40권1호
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• pp.66.3-67
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• 2015

Without scrutinizing reflection, the plasma comprising a coronal loop is usually regarded to reside within a flux rope. This picture seems to have been adopted from laboratory plasma pinches, in which a plasma of high density and pressure is confined in the vicinity of the flux rope axis by magnetic tension and magnetic pressure of the concave inward magnetic field. Such a configuration, in which the plasma pressure gradient and the field line curvature vector are almost parallel, however, is known to be vulnerable to ballooning instabilities (to which belong interchange instabilities as a subset). In coronal loops, however, ideal MHD (magnetohydrodynamic) ballooning instabilities are impeded by a very small field line curvature and the line-tying condition. We, therefore, focus on non-ideal (resistive) effects in this study. The footpoints of coronal loops are constantly under random motions of convective scales, which twist individual loop strands quite randomly. The loop strands with the axial current of the same direction tend to coalesce by magnetic reconnection. In this reconnection process, the plasma in the loop system is redistributed in such a way that a smaller potential energy of the system is attained. We have performed numerical MHD simulations to investigate the plasma redistribution in coalescence of many small flux ropes. Our results clearly show that the redistributed plasma is more accumulated between flux ropes rather than near the magnetic axes of flux ropes. The Joule heating, however, creates a different temperature distribution than the density distribution. Our study may give a hint of which part of magnetic field we are looking to in an observation.