• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.820-831
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• 2015

In a deregulated electricity market, congestion of the transmission lines is a major problem the independent system operator (ISO) would face. Rescheduling of generators is one of the most practiced techniques to alleviate the congestion. However, not all generators in the system operate deterministically and independently, especially wind power generators (WTGs). Therefore, a novel optimal rescheduling model for congestion management that accounts for the uncertain and correlated power sources and loads is proposed. A probabilistic power flow (PPF) model based on 2m+1 point estimate method (PEM) is used to simulate the performance of uncertain and correlated input random variables. In addition, the impact of direct electricity purchase contracts on the congestion management has also been studied. This paper uses artificial bee colony (ABC) algorithm to solve the complex optimization problem. The proposed algorithm is tested on modified IEEE 30-bus system and IEEE 57-bus system to demonstrate the impacts of the uncertainties and correlations of the input random variables and the direct electricity purchase contracts on the congestion management. Both pool and nodal pricing model are also discussed.

• Journal of Electrical Engineering and Technology
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• 제7권2호
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• pp.141-150
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• 2012

The present study examines an efficient congestion management system compatible with the evolving environment. The key is to build an information model shared and exchanged for marketbased solutions to alleviate congestion. Traditional methods for congestion management can be classified into two categories, i.e., the centralized scheme and the decentralized scheme, depending on the extent to which the independent system operator (ISO) is involved in market participants' (MPs) activities. Although the centralized scheme is more appropriate for providing reliable system operation and relieving congestion in near real-time, the decentralized scheme is preferred for supporting efficient market operation. The minimum set of information between the ISO and MPs for decentralized scheme is identified: i) congestion-based zone, ii) Power Transfer Distribution Factors, and iii) transmission congestion cost. The mathematical modeling of the proposed information is expressed, considering its process of making effective use of information. Numerical analysis is conducted to demonstrate both cost minimization from the MP perspective and the reliability enhancement from the ISO perspective based on the proposed information exchange scheme.

• Journal of Electrical Engineering and Technology
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• 제9권1호
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• pp.90-97
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• 2014

Nash Cournot Equilibrium (NCE) has been widely used in a competitive electricity market to analyze generation firms' strategic production quantities. Congestion on a transmission network may lead to a mixed strategy NCE. Mixed strategy is complicated to understand, difficult to compute, and hard to implement in practical market. However, Stackelberg model based equilibrium does not have any mixed strategy, even under congestion in a transmission line. A guide to understanding mixed strategy equilibrium is given by analyzing a cycling phenomenon in the players' best choices. This paper connects the concept of leader-follower in Stackelberg model with relations between generation firms on both sides of the congested line. From the viewpoint of social welfare, the surplus analysis is presented for comparison between the NCE and the Stackelberg equilibrium (SE).

• 한국산업정보학회논문지
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• 제10권1호
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• pp.9-15
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• 2005

관련 기업 및 ISP 업체에게는 투자의 매력을 부여하며 인터넷의 사용시간대 및 사용량에 따라 빈약한 사용자, 건강한 사용자, 과다한 사용자 등으로 구분하여 차등요금을 부여하는 합리적인 전략이 필요하다. 이 논문에서 차등요금부과의 타당성을 검토한다. 그리고 로지스틱 회귀모형을 이용하여 혼잡에 따른 차등요금, 지연시간, 접속만족도 등에 따라 실제적으로 인터넷 사용자들이 인터넷 접속을 얼마나 유지하는 지를 측정할 수 있는 관련 예측모델을 제시한다. 이러한 예측모델을 이용하여 인터넷 접속 또는 비접속 확률을 예측하는 분석률은 $69.5\%$이었음을 확인하였다.

• Journal of applied mathematics & informatics
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• 제12권1_2호
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• pp.395-408
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• 2003

Common Channel Signaling(CCS) networks need special controls to avoid overload of signaling networks and degradation of call process-ing rate, since they play an important role of controlling communication transfer networks. Congestion control and flow control mechanisms are well described in ITU-T recommendation on Signaling System No.7(SS7). For the practical provisions, however, we need an analysis on the relation among service objects, system requirements and implementation of congestion control algorithms. SS7 provides several options for controlling link congestion in CCS networks. In this paper we give a general queueing model of congestion control algorithm which covers both the international and national options. From the queuing model, we obtain the performance parameters such as throughput, message loss rate and mean delay for the international option. To show the performance of the algorithm, some numerical results are also given.

• 한국멀티미디어학회논문지
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• 제23권10호
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• pp.1270-1285
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• 2020

As a representative concept of the fourth industrial revolution era where everything is digitized, digital twin means analyzing and optimizing a complex system using a simulation model synchronized with the system. In this paper, we propose a digital twin simulation model for the efficient operation of urban railways in Busan. Due to the geopolitical nature of Busan, where there are many mountains and narrow roads, the railways are more useful than other public transportation. However, this inversely results in a high level of congestion, which is an inconvenience to citizens and may be fatal to the spread of the virus, such as COVID19. Considering these characteristics, the proposed model analyzes the congestion level of the railways in Busan. The model is developed based on a mathematical formalism called discrete-event system specification and deduces the congestion level and the average waiting time of passengers depending on the train schedule. In addition, a new schedule to reduce the congestion level is derived through particle swarm optimization, which helps the efficient operation of the railways. Although the model is developed for the railways in Busan, it can also be used for railways in other cities where a high level of congestion is a problem.

• 전기학회논문지P
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• 제63권3호
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• pp.131-137
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• 2014

It is expected that there will be delay of scheduled transmission network reinforcement and huge investment of renewable energy resources in Korea. As transmission capacity expansion delayed, supplying power to Seoul metropolitan area will not be increased as scheduled. In addition, uncertain renewable energy out of Seoul metropolitan area can cause transmission congestion in the future power system. These two combining effects will make the difference in locational marginal prices(LMP) and congestion costs increase. In that sense, this paper will analyze how much the congestion costs for Korea power system are incurred in the future power system. Most of previous approaches to analyze the congestion costs for electric power system are based on the optimal power flow model which cannot deal with hourly variation of power system. However, this study attempted to perform the analysis using market simulation model(M-Core) which has the capability of analyzing the hourly power generation cost and power transmission capacity, and market prices by region. As a result, we can estimate the congestion costs of future power system considering the uncertainty of renewable energy and transmission capacity.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2006년도 춘계학술발표대회
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• pp.913-916
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• 2006

SNMP는 망 관리 시스템을 구현하는데 있어서 비교적 단순하고 안전한 일대일 통신 방안을 제공하고 있다. 원격 회의 또는 강의, VoIP, 네트워크 게임 등의 다양한 통신 컨텐츠에 대해 인터넷을 통한 이용이 급증하면서 UDP 기반의 SNMP 통신에 있어서도 Congestion Control을 적용하기 위한 방안이 필요하게 되었다. 본 논문에서는 UDP에서 Congestion Control을 이용하는 DCCP를 이용하여 SNMP를 기반의 망 관리 시스템을 구축할 수 있는 구조를 제안한다.

• 한국통신학회논문지
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• 제32권9A호
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• pp.916-922
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• 2007

Wireless networks (WNs) are developed and applied widely in a lot of areas. Now, a new generation of wireless networks is coming, and that is Wireless Mesh Network (WMN). At present, there are not so many researches which deal on this area. Most researches are derived from Mobile Ad hoc Networks (MANET) and WNs. In WMNs, there are some applications that require real-time delivery. To guarantee this, rate control and congestion control are needed. This problem leads to optimization issue in transport layer. In this paper, we propose a mathematical model which is applied in rate and congestion control in WNMs. From this model, we optimize rate and congestion control in WMNs by maximizing network utility. The proposed algorithm is implemented in distributed way both in links and sources.

• 한국경영과학회지
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• 제34권1호
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• pp.61-83
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• 2009

This study developed a variable demand traffic assignment model by stable dynamics. Stable dynamics, suggested by Nesterov and do Palma[19], is a new model which describes and provides a stable state of congestion in urban transportation networks. In comparison with the user equilibrium model, which is based on the arc travel time function in analyzing transportation networks, stable dynamics requires few parameters and is coincident with intuitions and observations on congestion. It is therefore expected to be a useful analysis tool for transportation planners. In this study, we generalize the stable dynamics into the model with variable demands. We suggest a three stage optimization model. In the first stage, we introduce critical travel times and dummy links and determine variable demands and link flows by applying an optimization problem to an extended network with the dummy links. Then we determine link travel times and path flows in the following stages. We present a numerical example of the application of the model to a given network.