• 한국태양에너지학회 논문집
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• 제35권3호
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• pp.57-63
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• 2015

This paper presents a solution by introducing energy storage system(ESS) to solve an annual blackout due to a typhoon or electrical failure in Udo Island. This island is now receiving electrical power through undersea cables from the Jeju Island. During blackout period, ESS will supply the electricity. And it is necessary to estimate the ESS capacity and control the transient state for the operation of stable power system. For the verification of proposed method, ESS capacities have been estimated according to base load and the minimum capacity of only home appliance in Udo Island. Also, in case of restoring from the fault, the algorithm for synchronization is proposed. Finally, the simulation results by using the PSCAD/EMTDC program will show the feasibility.

• 전기학회논문지
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• 제68권1호
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• pp.1-7
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• 2019

Due to the highly concentrated power plants integrated through the limited transmission lines in Korea, a Special Protection System(SPS) has been applied to stabilize the power systems by instantly tripping the pre-determined generators in a large-scaled power plant when a fault occurs on the drawing transmission lines. Moreover, power outputs of those generators are constrained to avoid any activation of Under Frequency Load Shedding(UFLS) even after those generators are tripped by SPS action. For this, this paper proposes a method for calculating the required capacity of Energy Storage System(ESS) expected to relieve the operating constraints to generators using its fast response for controlling power system frequency. The proposed method uses the generator acceleration energy to derive the stable condition during the SPS action. In addition, its effectiveness is verified by the case studies adopting actual SPS operations in Korean power systems.

• 한국초전도ㆍ저온공학회논문지
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• 제11권3호
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• pp.35-39
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• 2009

The study for a protective relay system is one of the important technical issues on the power system application of Superconducting Fault Current Limiter (SFCL). We used Real Time Digital Simulator(RTDS) to study the true interaction of the protection system with the power system. RTDS modeling of SFCL is necessary to the detailed protective relay tests. In this paper, we developed an analysis model using RTDS for studying the transient behavior of 22.9kV SFCL and carried out closed-loop testing of protective relays in distribution power system with the developed SFCL model. The SFCL model has the operation mechanism of 22.9kV hybrid SFCL being developed by LSIS and KEPRI in Korea. The parameters of the model are based on the test data of the real SFCL. Power system planners and operators can solve the expected problems in power system application of SFCL using protective relay testing results.

• 대한전자공학회논문지SP
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• 제46권3호
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• pp.125-137
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• 2009

음향방출 기법은 작동중인 상태에서 기계 설비를 비파괴 검사할 수 있는 기법이며, 균열성장 같은 장애의 신뢰성 있는 감시를 위해서 순간적인 균열신호뿐만 아니라 동특성을 이용하는 것이 중요하다. 균열성장을 검출하기 위해 널리 사용되는 물리적 파괴 3단계는 음향방출 현상이 시간에 따라 서로 겹치는 문제점이 있어 정확한 균열성장 시간을 추정하기 어렵다. 제안한 패턴인식 기법은 오경보와 미탐지를 최소화하기 위해서 음향방출 동특성을 입력으로 사용하고, 균열성장 시간을 정확히 추정하기 위해 시간에 따른 클러스터링 기법을 사용한다. 실험결과는 제안한 패턴인식 기법이 압력의 변화에 의한 음향방출의 변화의 강인함 때문에 실용화에 효율적임을 보여준다.

• Journal of Electrical Engineering and Technology
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• 제10권1호
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• pp.379-387
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• 2015

A custom power device provides an integrated solution to the present problems that are faced by the utilities and power distribution. In this paper, a new controller is designed which is connected to a multiconverter unified power quality conditioner (MC-UPQC) for improving the power quality issues adopted modified synchronous reference frame (MSRF) theory with Fuzzy logic control (FLC) technique. This newly designed controller is connected to a source in order to compensate voltage and current in two feeders. The expanded concept of UPQC is multi converter-UPQC; this system has a two-series voltage source inverter and one shunt voltage source inverter connected back to back. This configuration will helps mitigate any type of voltage / current fluctuations and power factor correction in power distribution network to improve power quality issues. In the proposed system the power can be conveyed from one feeder to another in order to mitigate the voltage sag, swell, interruption and transient response of the system. The control strategies of multi converter- UPQC are designed based on the modified synchronous reference frame theory with fuzzy logic controller. The fast dynamics response of dc link capacitor is achieved with the help of Fuzzy logic controller. Different types of fault conditions are taken and simulated for the analysis and the results are compared with the conventional method. The relevant simulation and compensation performance analysis of the proposed multi converter-UPQC with fuzzy logic controller is performed.

• 대한전자공학회논문지SD
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• 제42권12호
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• pp.91-102
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• 2005

최근의 저 전력 컴퓨터 시스템은 내장 프로세서의 성능 향상과 공정 기술의 발전을 통한 디바이스 크기 감소로 인해 전압 변동, 커플링 효과 등으로 인한 SEU(single event upset)로 모델링 되는 천이고장으로 인한 예기치 못한 동작 중 에러 발생가능성이 매우 높아지고 있다. 제안하는 방식은 프로세서가 처리하는 프로그램 분기 흐름상에서 에러를 검출하는 효과적인 watchdog 프로세서 구조로서, 기존 방식이 가지는 오버헤드를 줄이면서 프로그램 내부에서 빈번히 발생되는 루프를 매번 검사할 때, 동일한 동작을 watchdog 프로세서가 반복함으로써 생기는 비효율적인 메모리 접근, 버스 점유 경쟁등과 같은 추가적인 시스템 수준의 오버헤드를 줄이는 새로운 방법을 제안하였다. 본 논문은 기존의 실시간 분기 및 제어 흐름 연구에서는 다루지 않았던 루프 검출 및 예측 기능을 추가함으로써 실제 시스템 적용에 보다 적합한 비용 효율적인 구조를 제안하고 있다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.1659-1663
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• 1991

A new control design methodology is presented here which is based on a nonlinear time-series reference model. It is indicated by highly nonlinear simulations that such designs successfully stabilize troublesome aircraft maneuvers undergoing large changes in angle of attack as well as large electric power transients due to line faults. In both applications, the nonlinear controller was significantly better than the corresponding linear adaptive controller. For the electric power network, a flexible a.c. transmission system (FACTS) with series capacitor power feedback control is studied. A bilinear auto-regressive moving average (BARMA) reference model is identified from system data and the feedback control manipulated according to a desired reference state. The control is optimized according to a predictive one-step quadratic performance index (J). A similar algorithm is derived for control of rapid changes in aircraft angle of attack over a normally unstable flight regime. In the latter case, however, a generalization of a bilinear time-series model reference includes quadratic and cubic terms in angle of attack. These applications are typical of the numerous plants for which nonlinear adaptive control has the potential to provide significant performance improvements. For aircraft control, significant maneuverability gains can provide safer transportation under large windshear disturbances as well as tactical advantages. For FACTS, there is the potential for significant increase in admissible electric power transmission over available transmission lines along with energy conservation. Electric power systems are inherently nonlinear for significant transient variations from synchronism such as may result for large fault disturbances. In such cases, traditional linear controllers may not stabilize the swing (in rotor angle) without inefficient energy wasting strategies to shed loads, etc. Fortunately, the advent of power electronics (e.g., high-speed thyristors) admits the possibility of adaptive control by means of FACTS. Line admittance manipulation seems to be an effective means to achieve stabilization and high efficiency for such FACTS. This results in parametric (or multiplicative) control of a highly nonlinear plant.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권4호
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• pp.2002-2019
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• 2017

RPL routing protocol for low-power and lossy networks is an Internet Engineering Task Force (IETF) recommended IPv6 based protocol for routing over Low power Lossy Networks (LLNs). RPL is proposed for networks with characteristics like small packet size, low bandwidth, low data rate, lossy wireless links and low power. RPL is a proactive routing protocol that creates a Directed Acyclic Graph (DAG) of the network topology. RPL is increasingly used for Internet of Things (IoT) which comprises of heterogeneous networks and applications. RPL proposes a single path routing strategy. The forwarding technique of RPL does not support multiple paths between source and destination. Multipath routing is an important strategy used in both sensor and ad-hoc network for performance enhancement. Multipath routing is also used to achieve multi-fold objectives including higher reliability, increase in throughput, fault tolerance, congestion mitigation and hole avoidance. In this paper, M-RPL (Multi-path extension of RPL) is proposed, which aims to provide temporary multiple paths during congestion over a single routing path. Congestion is primarily detected using buffer size and packet delivery ratio at forwarding nodes. Congestion is mitigated by creating partially disjoint multiple paths and by avoiding forwarding of packets through the congested node. Detailed simulation analysis of M-RPL against RPL in both grid and random topologies shows that M-RPL successfully mitigates congestion and it enhances overall network throughput.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.343-347
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• 1999

YBCO film을 이용한 meander 형태의 저항형 한류기에서 고장이 발생하였을 때 초기의 과도상태에서 볼수 있는 첨두전류를 억제하기 위하여 shunt 저항을 병렬로 취부한 경우의 전기적특성을 살펴보았다. 인가전압을 16.5 V$_{peak}$로 가하고 R$_0$는 1 ${\omega}$,R$_L$을 7.7 ${\omega}$으로 하고 shunt 저항을 5 ${\omega}$으로 하였을 때 약 12.2 A$_{peak}$의 전류값에서 최초quench가 발생하였으며 초전도 한류소자에 quench 발생으로 인한 저항이 발생함과 동시에 I$_1$으로 흐르던 사고전류의 일부가 shunt 저항이있는 I$_2$으로 서서히 분로하여 첨두전류가 거의 발생하지 않았다. 이때 초전도 한류기를 적용하지 않은 경우 최대 사고전류는 약 16.5 A$_{peak}$이었으며 초전도 한류기를 적용한 경우는 최대 한류전류값이 9 A$_{peak}$에서 4주기후에는 5.8 A$_{peak}$이었다. 인가전압 V$_0$=113 V$_{peak}$이고 표준저항 R$_0$는 1${\omega}$, 그리고 R$_L$을 7.7 ${\omega}$으로 하고 shunt 저항을 5 ${\omega}$으로 하였을 때 사고각 0 $^{\circ}$에서 사고전류값이 최고 23.0 A$_{peak}$까지 상승하고 이후 일정한 값을 유지하였다. 일반적으로 사고발생 직후에는 전류변화율에 의하여 전류값의 급격한 상승을 보이지만 shunt 저항이 전류분류의 역할을 수행하여 첨두전류는 거의 발생하지 않았다. 또한 상온의 gold층의 저항을 감안했을 때 사고발생후 약 36msec 후에 상온에 도달하였으며 shunt 저항이 없는 경우의 11 msec에 비하여 약 3배이상 길어졌다. 사고각 45 $^{\circ}$와 90 $^{\circ}$인 경우는 반복실험에 의한 시편의 특성저하(degradation)에 의하여 정상상태에서 초전도체에 흐르는 전류가 약간 발생하였다. 계통의 신뢰성이 중요한 요소로 작용하는 실제운전에서는 시편의 특성저하에 의한 quench전류의 감소를 감안하여 적절한 운전조건을 도출하여야 한다. 이상에서 앞으로는 장기간의 실제운전 조건을 고려하여 시편의 특성저하(degradation)와 가혹조건에 대한 전기적 특성에 대한 연구를 병행하고자 한다.