• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 A
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• pp.739-741
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• 2005

The congestion cost caused by transmission capacities is an important issue in a competitive electricity market. To allocate the congestion cost equitably, the active constraints in a constrained dispatch and the sequence of these constraints should be considered. A multi-stage method which was proposed by H.S. Jung reflects the effects of both the active constraints and the sequence. In a multi-stage method, the types of congestion are analyzed in order to consider the sequence, and the relationship between congestion and the active constraints is derived in a mathematical way. But in some cases, the inactive constraints can affect the congestion sequence and it is reasonable to allocate the congestion cost to them.

• 대한전기학회논문지:전력기술부문A
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• 제50권12호
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• pp.549-555
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• 2001

Due to the development of information technology, the operating power systems under the deregulated environment has the advantages of a introduction of the market function, a competition in sales and purchases of Power, as well as the difficulty of maintaining reliability on the same or high level with it in a monopolistic market. This paper presents a basic scheme of the congestion management in the Korea electricity market under the deregulated environment. We investigated some cases of the congestion management in the world and the effects of the congestion management in the power systems. A basic idea of the congestion management in the Korea is presented based on the analysis of transmission congestion management in the competitive electricity market.

• International Journal of Computer Science & Network Security
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• 제22권10호
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• pp.191-200
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• 2022

Constrained Application Protocol (CoAP) is a standardized protocol by the Internet Engineering Task Force (IETF) for the Internet of things (IoT). IoT devices have limited computation power, memory, and connectivity capabilities. One of the significant problems in IoT networks is congestion control. The CoAP standard has an exponential backoff congestion control mechanism, which may not be adequate for all IoT applications. Each IoT application would have different characteristics, requiring a novel algorithm to handle congestion in the IoT network. Unnecessary retransmissions, and packet collisions, caused due to lossy links and higher packet error rates, lead to congestion in the IoT network. This paper presents an adaptive congestion control protocol for CoAP, Adaptive Congestion Control with a Backoff algorithm (ACCB). AACB is an extension to our earlier protocol AdCoCoA. The proposed algorithm estimates RTT, RTTVAR, and RTO using dynamic factors instead of fixed values. Also, the backoff mechanism has dynamic factors to estimate the RTO value on retransmissions. This dynamic adaptation helps to improve CoAP performance and reduce retransmissions. The results show ACCB has significantly higher goodput (49.5%, 436.5%, 312.7%), packet delivery ratio (10.1%, 56%, 23.3%), and transmission rate (37.7%, 265%, 175.3%); compare to CoAP, CoCoA+ and AdCoCoA respectively in linear scenario. The results show ACCB has significantly higher goodput (60.5%, 482%,202.1%), packet delivery ratio (7.6%, 60.6%, 26%), and transmission rate (40.9%, 284%, 146.45%); compare to CoAP, CoCoA+ and AdCoCoA respectively in random walk scenario. ACCB has similar retransmission index compare to CoAp, CoCoA+ and AdCoCoA respectively in both the scenarios.

• 한국멀티미디어학회논문지
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• 제8권9호
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• pp.1208-1215
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• 2005

멀티캐스트를 이용한 멀티미디어 응용에서는 다수의 수신자들로부터 피드백을 수신할 경우 폭주로 인한 혼잡이 발생하여 전송률이 낮아지는 문제가 발생한다. 이를 위해 계층적 대표자 기법이 제안되었다. 그러나 수신자 전체를 고려한 전송률 조절로 인하여 혼잡이 없는 지역의 전송률도 같이 낮아지는 문제가 발생한다. 본 논문에서는 이러한 문제를 해결하기 위해 지역대표자를 두었다. 지역대표자는 해당 그룹의 전송률이 최소 유지임계치 미만일 경우, 혼잡 수신자를 전송률 계산에서 제외시켜 다시 계산한다. 이렇게 함으로써 혼잡이 발생하지 않는 지역의 전송률이 같이 낮아지는 문제를 개선하였다. 실험을 통한 결과를 볼 때 기존의 기법보다 더 안정적인 전송률로 조절됨을 보였다.

• 한국멀티미디어학회논문지
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• 제9권3호
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• pp.315-322
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• 2006

IP 멀티캐스트를 이용한 응용에서는 혼잡지역의 전송률 감소로 인하여 혼잡이 발생하지 않은 지역의 전송률도 낮아져 가용 대역폭 낭비가 발생한다. 본 논문에서는 이러한 문제를 해결하기 위하여 IP 멀티캐스트와 오버레이 멀티캐스트를 이용한 동적 멀티캐스트 기법을 제안한다. 제안 기법에서는 오버레이 멀티캐스팅을 위한 지역 대표자를 선택하고, 그룹 전송률이 전송률 임계치 이하일 경우 대표자가 복제한 패킷을 전송할 수 있도록 하였다. 실험 결과 제안 기법이 대역폭을 더 효율적으로 이용함을 알 수 있었다.

• 한국통신학회논문지
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• 제25권8A호
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• pp.1177-1185
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• 2000

본 논문에서는 긴 전파 지연과 높은 에러율을 지닌 위성링크에 TCP를 사용하는 경우 나타나는 문제점을 도출하고 그에 대한 성능향상방안으로 ENA(Error Notification Ack) 알고리즘을 제안했다. TCP는 에러에 의한 세그먼트 손실과 Network Congestion에 의한 손실을 구분하지 못하고 두 경우 모두 Network Congestion 으로 판단한 후 Slow Start나 Congestion Aboidance 알고리즘을 적용시킨다 위성링크에서는 에러에 의한 세그먼트 손실이 자주 발생하는데 이손실을 Network Congestion에 의한 손실로 받아들여 매번 Congestion Control 알고리즘을 적용시킨다 그로인해 전송률을 줄어들고 성능은 급격히 떨어진다. 본 논문에서는 에러에 의한 손실과 Congestion 의한 손실을 구분해 주는 ENA 알고리즘을 제안하고 구현 방법 또한 제시하였다 그리고 ENA 알고리즘을 Tahoe, Reno. Sack TCP에 적용하여 성능의 변화를 비교 분석했다 그 결과 에러율이 높을수록 성능이 더 향상됨을 알수 있었다.

• 전기학회논문지
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• 제65권12호
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• pp.1965-1970
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• 2016

This paper studies generator rescheduling technique for congestion management in power system with wind farms. The proposed technique is formulated to minimize the rescheduling cost of conventional and wind generators to alleviate congestion subject to operational line overloading. The generator rescheduling method has been used with incorporation of wind farms in the power system. The locations of wind farms are selected based upon power transfer distribution factor (PTDF). Because all generators in the system do not need to participate in congestion management, the rescheduling has been done by generator selection based on the proposed generator sensitivity factor (GSF). The selected generators have been rescheduled using linear programming(LP) optimization techniques to alleviate transmission congestion. The effectiveness of the proposed methodology has been analyzed on IEEE 14-bus systems.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 A
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• pp.66-68
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• 2005

In Korea power system, the transfer capability of transmission line is limited by the voltage stability and it is difficult to construct new iron tower due to incremental interest for environmental problem and construction costs. Recently, HTS cable could be one of the countermeasures to solve the transfer limit because of it is transported to large power with compact size However, the characteristic of HTS cable have a various problem. This paper presents the effects of congestion cost reduction by the application of HTS (High-Temperature Superconducting) cable. In this paper, the transmission ability before and after application of HTS cable are examined in a viewpoint for voltage stability. therefore, the effects of congestion cost reduction by HTS cable.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 A
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• pp.728-730
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• 2004

Transmission congestion is one of the Key factors to local market power in competitive electricity markets. Other players' strategy is also considered. This paper presents an alternative methodology in market power under transmission congestion and other players' strategy. The proposed methodology was demonstrated with the Optimal Power Flow(OPF). Case study is fulfilled by GAMS simulation.

• 대한전기학회논문지:전력기술부문A
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• 제50권6호
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• pp.259-264
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• 2001

The electric utility industry around the world is undergoing a revolutionary transition from vertically integrated monopoly structures to a competitive structures. Competition in an open transmission access(OTA) makes the market participants access easily the transmission system in a non-discriminatory and equitable manner. The competitions of suppliers and customers make the electric market price change every hour. This paper presents a web program in the internet environment with a function of optimal power flow(OPF) calculation. The Web program gives the nodal marginal cost and the congestion charge using the shadow prices resulted from OPF. This web program is realized by a Perl and JAVA languages, and using the common gateway interface(CGI).