• 한국컴퓨터정보학회논문지
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• 제21권1호
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• pp.59-64
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• 2016

This paper suggests heuristic algorithm with O(mn) polynomial time complexity using Excel for partially survivable networks optimization problem of cellular telecommunication systems with m cells and n hubs. This problem only can be get the solution using linear programming or LINGO software package. The proposed algorithm connects the cell to hubs in ring network with minimum cost as the connection diversity of each cell. If the traffic of ring network (T) is T>2K for ring capacity (K), we adjust the maximum cost hub to MTSO that has a ascending order of (D/DC)/${\Delta}^+$ cell with each cell traffic demand (D) and ${\Delta}^+$=(MTSO cost-maximum cost hub) than we get the $T{\leq}2K$. Finally, we adjust MTSO to the removed maximum cost hub for the cell with 2K-$T{\geq}$(D/DC) and $_{max}{\Delta}^-$. While we using like this simple method, the proposed algorithm can be get the same optimal solution for experimental data as linear programing and LINGO software package.

• 한국철도학회논문집
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• 제11권2호
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• pp.203-210
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• 2008

바퀴와 BLDC전동기 일체형으로 구성되는 Hub Wheel 전동기는 감속기가 없는 직접 구동방식으로서 저소음 고효율의 운전이 가능하여 경전철의 구동부로 활용이 가능하다. 하지만 Hub Wheel 전동기는 속도계측을 위한 센서의 장착이 용이하지 않다. 전동기의 원활한 속도 제어를 위해서는 별도의 속도 계측을 위한 방법이 요구된다. 본 논문에서 입력이 적극 반영된 간단한 수학적 시스템 모델을 가지고 이산 칼만 필터를 사용하여 전동기 속도를 추정하고 이를 이용하여 속도제어를 하는 방법을 제시한다.

• 한국유체기계학회 논문집
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• 제15권2호
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• pp.57-62
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• 2012

The constant air volume flow fan can maintain constant flow rate to the wide range of exit pressure. Therefore, the use of this fan is increasing recently for ventilation of high building. Brushless DC motor is adopted to this fan because that has advantages of compactness and performance. But this type of motor protrude from impeller hub side to fan inlet. The Impeller inlet flow is influenced by size of this obstacle called hub. In this paper, the influence of hub shape on the fan performance characteristics are experimentally and numerically analyzed. CFX 12.0 is used to perform the fan internal flow analysis and numerical results are compared with the experiments. Depending on hub shape, internal loss is generated and the performance and efficiency are reduced. The best performance is occurred around $h/b_1$ = 0.25. The results of this study will be contribute to initial design of constant air volume flow fan development.

• Journal of Electrical Engineering and Technology
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• 제8권4호
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• pp.704-711
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• 2013

Data center is an information hub and resource for information-centric society. Since data center houses hundreds to ten thousands servers, networking and communication equipment, and supporting systems energy saving is one of the hottest issues for green data center. Among several solutions for green data center this paper introduces higher voltage direct current (DC) power feeding system. Contrary to legacy alternating current (AC) power feeding system equipped with Uninterruptible Power Supply (UPS), higher voltage DC power feeding system is reported to be a more energy efficient and reliable solution for green data center thanks to less AC/DC and DC/AC conversions. Main focus of this paper is on reliability issue for reliable and continuous operation of higher voltage DC power feeding system. We present different types of configuration of the power feeding systems according to the level of reliability. We analyze the reliability of the power feeding systems based on M/M/1/N+1/N+1 queueing model. Operation of the power feeding system in case of failure is also presented.

• 통상정보연구
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• 제18권4호
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• pp.55-78
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• 2016

uTradeHub 관련 선행연구들은 서비스 품질의 중요성을 일원론적 시각에서 파악했을 뿐 어떠한 서비스 품질속성을 우선적으로 향상시켜야 할지에 대한 연구는 부재한 상황이다. 본 연구에서는 Kano 모형에 의거 uTradeHub의 서비스 품질속성을 분류하고, Timko의 고객만족계수(CSC)와 평균만족계수(ASC)를 사용하여 uTradeHub 서비스 품질 제고를 위해 중점적으로 관리해야 하는 품질속성을 규명하였다. 설문조사를 통해 확보된 총105개의 유효자료를 실증분석에 사용하였으며, 연구결과를 요약하면 다음과 같다. 첫째, Kano모형에 의거 서비스 품질속성을 분류한 결과, 일원적 품질 12개, 당연적 품질 5개, 무관심 품질 2개가 도출되었다. 둘째, Timko의 고객만족계수(CSC)를 이용한 분석결과에서는 "고충 및 불만에 대한 사후처리"와 "비용절감", "업무처리의 효율성", "정확하고 유용한 정보 제공"이 만족계수(SC)의 상위에 랭크됨으로써 서비스 품질이 충족되면 고객만족이 특히 증가하는 품질속성으로 파악되었다. 반편 "고충 및 불만에 대한 사후관리", "상호작용", "문제발생시 즉각적 대응능력", "정확하고 유용한 정보제공", "업무처리의 효율성" 등은 불만족계수(DC)의 상위에 랭크됨으로써 서비스 품질이 충족되지 않으면 고객 불만이 특히 증가하는 품질속성으로 분석되었다. 셋째, 평균만족계수(ASC)에 의거 uTradeHub 서비스 품질 제고를 위해 중점 관리해야 하는 품질속성을 분석한 결과에서는 "고충 및 불만에 대한 사후관리", "비용절감", "정확하고 유용한 정보 제공", "업무처리의 효율성", "업무성과" 등이 상위 5위에 랭크됨으로써 지금보다 개선되면 만족도가 더 크게 증가하지만 악화되면 만족도가 훨씬 더 감소하는 품질속성으로 분류되었다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.280-284
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• 1997

In this paper, Nonlinear VSS control based on bang-bang control concept is derived under the assumption that the control input is bounded. We try to derive control algorithm which has almost same performance as the time optimal control. We focus this control scheme on the real implementation of DC motor position controller of flexible link, i.e. we obtain the switching curves from the real data of DC motor system operating under the full maximum and minimum applied voltages. State space is separated into several regions and we set different switching surfaces in each region to reduce chattering problem. The efficiency of the proposed controller is compared with PID controller and it is shown that the controller converges fast than PID controller without chattering. The hybrid controller scheme is also proposed not only to control the position of hub but also to reduce the vibration of end tip of flexible link.

• Journal of Power Electronics
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• 제18권1호
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• pp.225-233
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• 2018

This paper proposes a universal system control strategy for voltage source converter (VSC) based high voltage direct current (HVDC) systems. The framework of the designed control strategy consists of five layer structures considering the topology and control characteristics of the VSC-HVDC system. The control commands sent from the topmost layer can be transmitted to the next layer based on the existing communication system. When the commands are sent to each substation, the following transmission of commands between the four lower layers are realized using the internal communication system while ignoring the communication delay. This hierarchical control strategy can be easily applied to any VSC-HVDC system with any topology. Furthermore, an integrated controller for each converter is designed and implemented considering all of the possible operating states. The modular-designed integrated controller makes it quite easy to extend its operating states if necessary, and it is available for any kind of VSC. A detailed model of a VSC-HVDC system containing a DC hub is built in the PSCAD/EMTDC environment. Simulation results based on three operating conditions (the start-up process, the voltage margin control method and the master-slave control method) demonstrate the flexibility and validity of the proposed control strategy.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.132-135
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• 2008

This paper presents a PLL(Phase Lock Loop) control method for speed control of high speed miniature BLDCM(Brushless DC Motor) using hall sensor. The Proposed PLL based speed control method uses a only phase shift between reference pulse signal according to speed reference and actual pulse signal from hall sensor. It doesn't use any speed calculation, and calculates a direct current reference from phase shift. The current reference is changed to reduce the phase shift between reference and actual pulse. So the actual speed can keep the reference speed. The proposed control scheme is very simple but effective speed control is possible.