• 한국전자통신학회논문지
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• 제15권6호
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• pp.1131-1136
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• 2020

협력 네트워크는 중계기를 이용하여 신호를 전송하고, 수신기에서는 여러 중계기를 통해서 수신된 신호를 결합하여 복조함으로써 통신성능을 향상시킬 수 있다. 본 논문에서는 송신기-중계기 사이에서는 일반적인 변조 방식을 사용하고 중계기-수신기 사이에서는 공간 시간 코드 방식을 적용하는 협력 네트워크 시스템을 가정하여, 자원 할당에 따른 효과를 분석한다. 일반적인 변조 방식은 동기 변조 방식과 차등 변조 방식 두 가지를 고려하고 공간 시간 코드 방식은 차등 변조 방식을 적용한다. 자원 할당은 중계기의 위치와 전송에너지를 고려하며 중계기의 개수에 따른 성능 또한 분석한다.

• Journal of Electrical Engineering and Technology
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• 제3권3호
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• pp.363-372
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• 2008

In this paper, knowledge-based approach using Support Vector Machines (SVMs) are used for estimating the coordinated zonal settings of a distance relay. The approach depends on the detailed simulation studies of apparent impedance loci as seen by distance relay during disturbance, considering various operating conditions including fault resistance. In a distance relay, the impedance loci given at the relay location is obtained from extensive transient stability studies. SVMs are used as a pattern classifier for obtaining distance relay co-ordination. The scheme utilizes the apparent impedance values observed during a fault as inputs. An improved performance with the use of SVMs, keeping the reach when faced with different fault conditions as well as system power flow changes, are illustrated with an equivalent 265 bus system of a practical Indian Western Grid.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권2호
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• pp.565-581
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• 2019

This paper investigates the wireless powered two way relay network (WPTWRN), where two single-antenna users and one single-antenna relay firstly harvest energy from signals emitted by a multi-antenna power beacon (PB) and then two users exchange information with the help of the relay by using their harvested energies. In order to improve the energy transfer efficiency, energy beamforming at the PB is deployed. For such a network, to explore the performance limit of the presented WPTWRN, an optimization problem is formulated to obtain the achievable rate region bounds by jointly optimizing the time allocation and energy beamforming design. As the optimization problem is non-convex, it is first transformed to be a convex problem by using variable substitutions and semidefinite relaxation (SDR) and then solve it efficiently. It is proved that the proposed method achieves the global optimum. Simulation results show that the achievable rate region of the presented WPTWRN architecture outperforms that of wireless powered one way relay network architecture. Results also show that the relay location has significant impact on achievable rate region of the WPTWRN.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 A
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• pp.220-222
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• 2001

This paper represents impedance calculation of the distance relay using PSCAD/EMTDC software for transmission line involving the UPFC (Unified Power Flow Controller) device, which is the most vigorous component of FACTS. The presence of the UPFC significantly affects the line parameters of transmission system, which are also influenced by the distance relay setting. Moreover depending on the UPFC location and its parameters, zones of setting the distance relay will be changed. The presence of the UPFC in the fault loop affects both voltage and current seen by relay. Therefore, the distance relay should be taken into account the variable injected voltage of the UPFC.

• KIEE International Transactions on Power Engineering
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• 제5A권2호
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• pp.144-151
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• 2005

This paper presents a framework for determining control strategies against unwanted tripping actions during relay operation that plays a very important role in cascading events leading to voltage collapse. The framework includes an algorithm for quick identification of possible zone 3 relay operation during voltage instability. Furthermore, it comes up with the control strategy of load shedding at the selected location with active power and relay margin criteria. In addition, Quasi Steady-State (QSS) simulation is employed to obtain time-related information that is valuable in the determination of control strategy. As a case study, an example applying the framework is shown with the modified New England 39-bus system.

• 전기학회논문지
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• 제56권11호
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• pp.1885-1891
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• 2007

This paper presents a distance relaying algorithm for phase-to-ground faults in transmission lines under Multi-Agent protection environment. In normal condition, a distance relay agent stores the latest states, e.g., voltage of source side, voltage of the opposite side and the loading conditions, etc., through communication between the agents. Once a fault occurs, the relay calculates the fault location using the knowledge about the states just before the fault happens. This stand-alone operation is to improve reliability under the fault condition at which the accuracy or time required for communication may not be guaranteed. The mathematical expression of fault location is derived through loop analysis, before hand, in the manner that both fault current from the opposite end and fault resistance are included implicitly so that their effects are minimized. The suggested algorithm is applied to a typical transmission system with two power sources on both ends to show its effectiveness.

• 대한전기학회논문지:전력기술부문A
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• 제52권3호
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• pp.183-192
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• 2003

This paper presents the real-time implemented distance relay algorithm which the fault distance is estimated with only local terminal information. When a single-phase-to-earth fault on a two-parallel transmission line occurs, the reach accuracy of distance relay is considerably affected by the unknown variables which are fault resistance, fault current at the fault point and zero- sequence current of sound line The zero-sequence current of sound line is estimated by using the zero sequence voltage which is measured by relaying location Also. the fault resistance is removed at the Process of numerical formula expansion. Lastly, the fault current through a fault point is expressed as a function of the zero-sequence current of fault line, zero-sequence current of sound line, and line, and fault distance. Therefore, the fault phase voltage can be expressed as the quadratic equation of the fault distance. The solution of this Quadratic equation is obtained by using a coefficient of the modified quadratic equation instead of using the square root solution method. After tile accurate fault distance is estimated. the mote accurate impedance is measured by using such an information.

• 방송공학회논문지
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• 제15권2호
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• pp.224-231
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• 2010

이 논문에서는 OFDM(orthogonal frequency division multiplexing)의 부반송파에 계층변조를 적용한 협력 중계 통신시스템의 성능을 분석한다. 협력 중계 통신시스템의 전송구조는 두 개의 시간 슬롯으로 구성된다. 첫 번째 시간 슬롯에서는 송신단이 변조된 신호를 중계기와 수신단으로 동시에 전송한다. 중계기는 송신단으로부터 수신한 신호를 복조하고 재변조 하여 두 번째 시간 슬롯동안 재변조된 신호를 수신단으로 전송한다. 협력 중계 통신시스템에서 송신단-중계기 채널과 송신단-수신단 채널의 SNR(signal to noise power ratio)은 다르다. 송신단은 두 채널의 SNR에 적합한 변조방식을 동시에 이용하기 위해 계층변조 방식을 사용한다. 계층변조를 사용하는 협력 중계 통신시스템의 비트 오율(bit error rate)은 계층변조의 비균등 비율에 의해 달라진다. 이 논문에서는 기존의 계층변조 방식의 비균등 비율에 대한 비트 오율 값을 이용하여 계층변조를 적용한 협력 중계 통신시스템의 비트오율을 유도하고, 모의실험을 통해 최소 BER을 얻을 수 있는 계층변조의 최적 비균등 비율을 찾는다. 또한 중계기의 위치에 따라 제안한 시스템의 성능을 분석하고 이 결과를 바탕으로 시스템의 성능을 최대화할 수 있는 중계기의 위치를 찾는다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2010년도 추계학술대회
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• pp.158-161
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• 2010

본 논문에서는 현재 3GPP에서 진행되고 있는 차세대 이동통신 기술 표준, 즉 LTE 시스템의 하향 링크 전송방식의 수신성능을 향상시키기 위해 기지국(BS)과 단말(MS) 사이에 릴레이(RS) 설치를 제안하고, BS의 위치와 설치된 RS의 거리를 각각 500m, 1000m로 하고 RS의 전송방식을 OFDMA와 SC-FDMA를 선택함으로써 수신성능을 높이기 위한 연구를 수행 하였다. 연구결과 RS의 위치가 BS와 가까울수록 RS에서는 SC-FDMA를 사용하는 것이 좋게 나왔고, 반대로 BS와 RS의 거리가 멀어질수록 RS에서는 OFDMA를 사용하는 것의 성능이 좋은 것으로 나왔다. 또한 BS와 MS 거리의 중심지역에서는 그 상황에 맞는 전송방식을 사용함으로써 시스템의 수신성능을 향상시킬 수 있었다.

• Journal of Electrical Engineering and Technology
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• 제1권2호
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• pp.137-144
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• 2006

This paper proposes novel protection schemes for grid-connected distributed generation (DG) units using the fault location algorithm. The grid-connected DG would be influenced by abnormal distribution line conditions. Identification of the fault location for the distribution lines at the relaying point of DG helps solve the problems of the protection relays for DG. The proposed scheme first identifies fault locations using currents and voltages measured at DG and source impedance of distribution networks. Then the actual faulted feeder is identified, applying time-current characteristic curves (TCC) of overcurrent relay (OCR). The method considering the fault location and TCC of OCR might improve the performance of the conventional relays for DG. Test results show that the method prevents the superfluous operations of protection devices by discriminating the faulted feeder, whether it is a distribution line where DG is integrated or out of the line emanated from the substation to which the DGs are connected.