• 한국통신학회논문지
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• 제34권3A호
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• pp.229-234
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• 2009

본 논문에서는 자원 재사용이 가능한 무선 멀티홉 시스템에서 RS (Relay Station)간 적응적으로 무선자원을 재사용하기 위한 요구 자원량 결정 기법을 제안한다. 멀티홉 시스템에서 BS (Base Station)는 RS 각각의 요구 자원량을 고려하여 RS에게 자원을 동적으로 할당할 수 있다. 이 때 RS간에 무선자원을 재사용하면 시스템의 사용 가능한 자원량이 증가하는 효과를 얻을 수 있다. BS는 같은 자원을 재사용하는 RS에게 일반적으로 동일한 자원을 할당하며, 이를 위해 RS들의 서로 다른 요구 자원량을 대표하는 하나의 값을 결정해 줄 필요가 있다. 본 논문에서는 각 RS의 요구 자원량과 buffer 사용비율을 바탕으로 재사용 RS들의 요구 자원량의 대표값을 적응적으로 결정하는 기법을 제시한다. 모의실험을 통해 제안한 기법이 멀티홉 시스템의 성능을 증대시킬 수 있음을 보였다. 재사용 RS들의 대표 요구 자원량 값을 고정적으로 적용하는 경우에 비해 제안된 적응적 기법을 적용했을 때 시스템 용량이 약 두 배까지 증대됨을 확인하였다.

• KIEE International Transactions on Power Engineering
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• 제2A권3호
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• pp.89-94
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• 2002

In this paper, a protection system using a Multi-Agent concept for power distribution networks is proposed. Every digital over current relay(OCR) is developed as an agent by adding its own intelligence, self-tuning and communication ability. The main advantage of the Multi-Agent concept is that a group of agents work together to achieve a global goal which is beyond the ability of each individual agent. In order to cope with frequent changes in the network operation condition and faults, an OCR agent, suggested in this paper, is able to detect a fault or a change in the network and find its optimal parameters for protection in an autonomous manner considering information of the whole network obtained by communication between other agents. Through this kind of coordination and information exchanges, not only a local but also a global protective scheme is completed. Simulations in a simple distribution network show the effectiveness of the suggested protection system.

• 전기학회논문지
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• 제59권1호
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• pp.19-25
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• 2010

Most faults are single-phase-to-ground fault in ungrounded system. The fault currents of single-phase-to-ground are much smaller than detection thresholds of measurement devices, so detecting single-phase-to-ground faults is difficult and important in ungrounded system. The protection coordination method using SGR(Selective Ground Relay) and OVGR(Overvoltage Ground Relay) is generally used in ungrounded system. But this method only detects fault line and it has the possibility of malfunction. This paper proposed to advanced protection coordination method in ungrounded system. The method just using zero-sequence current can detect fault line, fault phase, fault section at terminal device. The general protection method is used to back up protection. In the case study, the proposed method has been testified in demo system by Matlab/Simulink simulations.

• 통합자연과학논문집
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• 제11권1호
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• pp.44-50
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• 2018

In this paper, we propose a context-aware power management (CPM) scheme using beacons to reduce the power consumption of personal computers (PCs). In the proposed CPM scheme, the PC, smartphone, control server, and Internet of Things (IoT) device are necessary. PC users first log in the control server using their smartphones and select PCs to turn on. Then, the selected PCs automatically go into three different modes, i.e., sleep, shutdown, and standby power off modes, in order when the PC users leave the PCs without turning off them. Further, we develop a testbed with the proposed CPM scheme using the Arduino with Bluetooth low energy (BLE) and relay modules. Finally, it is shown that the proposed CPM scheme outperforms the conventional scheme in terms of the power consumption.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.547-548
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• 2015

In order to reduce error of the distance relay, we propose an improved fault locating scheme using DC offset removal filter. We were modeled 154 kV transmission system using ATP software in order to demonstrate the usefulness of proposed scheme, and applied to the proposed scheme using collected voltage signal and current signal by line-to-ground fault.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1994년도 Proceedings of the Korea Automatic Control Conference, 9th (KACC) ; Taejeon, Korea; 17-20 Oct. 1994
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• pp.257-262
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• 1994

This paper describes an autotuning fuzzy PID controller for a position control of DC serve motor. Because ZNM(Ziegler-Nichols Method) with relay feedback has the difficulty in re-tuning the PID parameters and adaptive method has complex algorithm, a new method to overcome those problems is required. The proposed scheme determines the initial PID gains by using ZNM with relay feedback, and then re-tunes the optimal PID parameters by using fuzzy expert system whenever control conditions are changed. To show the validity of the proposed method, a position control of DC servo motor is illustrated by computer simulation and is experimented by a designed controller.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 추계학술대회 논문집 학회본부
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• pp.131-136
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• 1995

This paper presents a functional ability improvement of auto-reclosing relay in the power transmission line protection. When the high speed auto-reclosing is successful, Auto-reclosing is practically valuable to improve the transient stability limit of a power system, but it is fail due to surviving fault, both electrical and mechanical stresses can result on the transformers and turbine-generator. It is true that the longer dead time of the reclosing relay gives the higher rate of successful reclosing, On the other hand, the power system does not always need high speed reclosing because of enough stability margin. This paper proposed "stability margin based dead time reclosing" in order to decrease not only the rate of unsuccessful reclosing, but the possibility of the harmful stress also. On-line transient stability assessment using artificial neural network, for implementing the proposed scheme, has studied and tested with resonable results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전력기술부문
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• pp.265-267
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• 2002

In this paper, the communication between Over-Current Relay agents is realized using DNP(Distributed Network Protocol), which is the standard communication protocol of distribution automation system in KEPKO. The key words in OCR agent communication are defined and represented by use of DNP application function code. And the DNP index for OCR agent is defined. The proposed communication scheme is tested by use of Communication Test Harness, a test tool for DNP protocol to show its soundness.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권3호
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• pp.273-288
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• 2010

In this paper, we propose a cooperative multi-relay scheme for a secondary system to achieve spectrum access along with a primary system. In the primary network, a primary transmitter (PT) transmits the primary signal to a primary receiver (PR). In the secondary network, N secondary transmitter-receiver pairs (ST-SR) selected by a centralized control unit (CCU) are ready to assist the primary network. In particular, in the first time slot, PT broadcasts the primary signal to PR, which is also received by STs and SRs. At STs, the primary signal is regenerated and linearly combined with the secondary signal by assigning fractions of the available power to the primary and secondary signals respectively. The combined signal is then broadcasted by STs in a predetermined order. In order to achieve diversity gain, STs, SRs and PT will combine received replicas of the primary signal, using selection combining technique (SC). We derive the exact outage probability for the primary network as well as the secondary network. The simulation results are presented to verify the theoretical analyses.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권12호
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• pp.5803-5819
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• 2017

In this paper, we proposed a contract theory based cooperative spectrum sharing scheme with joint power and bandwidth optimization under asymmetric information, where the primary user (PU) does not know the secondary users' (SUs) private information. To improve performance, PU needs to provide incentives to stimulate nearby SUs to help forward its signal. By using contract theory, PU and SUs' negotiations are modeled as a labor market. PU and SUs act as the employer and employees, respectively. Specifically, SUs provide labor (i.e. the relay power, which can be used for forwarding PU's signal) in exchange for the reward (i.e. the spectrum access bandwidth which can be used for transmitting their own signals). PU needs to overcome a challenge how to balance the relationship between contributions and incentives for the SUs. We study the optimal contract design which consists of relay power and spectrum access bandwidth allocation. We show that the most efficient SUs will be hired by the PU to attend the cooperative communication. PU can achieve the same maximum utility as in the symmetric information scenario. Simulation results confirm that the utility of PU is significantly enhanced with our proposed cooperative spectrum sharing scheme.