• 해양환경안전학회지
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• 제15권3호
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• pp.257-262
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• 2009

일체형 조류제어기인 UPFC는 FACTS 기기중 가장 효과적인 기기 중 하나이다. 본 논문에서는 전력시스템에서 UPFC의 최적위치를 결정하는 데 필요한 컴퓨터의 계산을 줄이는 방법에 대하여 기술한다. 이를 위해 UPFC 제어 변수들과 관련된 발전 비용의 민감도가 평가되었다. 모든 송전선로의 UPFC 민감도를 얻기 위해 단지 한 번의 최적조류제어만으로 해결하였다. 전력시스템에서 UPFC의 최적 위치를 알아내기 위해 여러 권선비와 가변 션트 어드미턴스로 구성된 이상변압기 모델을 사용하였다. 이 모델에서 UPFC 제어 변수들은 UPFC 입 출력의 전류와 전압에 대해서 종속되지 않는다. 민감도 방법은 그의 효율성을 파악하기 위해 IEEE 14 모선에서 파생된 5 모선시스템과 IEEE 14 모선시스템을 대상으로 실험하였다.

• Smart Structures and Systems
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• 제22권1호
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• pp.81-94
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• 2018

Automatic Generation Control (AGC) has functionally controlled the interchange power flow in order to suppress the dynamic oscillations of frequency and tie-line power deviations as a perturbation occurs in the interconnected multi-area power system. Furthermore, Flexible AC Transmission Systems (FACTS) can effectively assist AGC to more enhance the dynamic stability of power system. So, Static Synchronous Series Compensator (SSSC), one of the well-known FACTS devices, is here applied to accurately control and regulate the load frequency of multi-area multi-source interconnected power system. The research and efforts made in this regard have caused to introduce the Fractional Order Proportional Integral Derivative (FOPID) based SSSC, to alleviate both the most significant issues in multi-area interconnected power systems i.e., frequency and tie-line power deviations. Due to multi-objective nature of aforementioned problem, suppression of the frequency and tie-line power deviations is formularized in the form of a multi-object problem. Considering the high performance of Multi Objective Bees Algorithm (MOBA) in solution of the non-linear objectives, it has been utilized to appropriately unravel the optimization problem. To verify and validate the dynamic performance of self-defined FOPID-SSSC, it has been thoroughly evaluated in three different multi-area interconnected power systems. Meanwhile, the dynamic performance of FOPID-SSSC has been accurately compared with a conventional controller based SSSC while the power systems are affected by different Step Load Perturbations (SLPs). Eventually, the simulation results of all three power systems have transparently demonstrated the dynamic performance of FOPID-SSSC to significantly suppress the frequency and tie-line power deviations as compared to conventional controller based SSSC.

• 한국멀티미디어학회논문지
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• 제8권8호
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• pp.1088-1098
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• 2005

사용자의 의도와 주변 환경과 연관된 정보를 습득함으로서 사용자에게 최적의 서비스를 제공하기 위한 컨텍스트 인식은 유비쿼터스 컴퓨팅에 관련된 중요한 연구 중에 하나이다. 기존 연구는 컨텍스트-인식의 대상으로 사용자와 주변 환경으로 한정하고, 서비스를 제공하기 위하여 식별자 정보를 운영하는 서버나 센서를 연동한 센싱 기반의 미들웨어를 제시하고 있다. 사용자와 주변 환경으로 한정된 컨텍스트-인식서비스는 중복된 센싱과 불필요한 검색의 문제 및 사용자의 익명성 문제를 야기한다. 또한, 중앙 집중형의 컨텍스트-인식 시스템은 서비스의 관리와 운영을 위해 많은 비용 요구한다. 본 논문에서는 자생적 컨텍스트 서비스 모델을 제안하여 컨텍스트-인식 단계를 단순화하고, 사용자의 휴대용 디바이스에 컨텍스트-인식 정보를 분산 관리하는 미들웨어를 설계하여 기존 컨텍스트-인식 시스템의 관리 및 운영에서 발생하는 문제점을 최소화 한다.

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.719-728
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• 2015

This paper presents the results of field tests on Voltage Management System (VMS) using hybrid voltage control, which utilizes coordinated controls of various reactive power resources such as generators, FACTS and switched shunt devices to regulate the pilot bus voltage in a voltage control area. It also includes the results of performance test on RTDS-based test bed in order to validate the VMS before installing it in Jeju power system. The main purpose of the system is adequately to regulate the reactive power reserve of key generators in a normal condition with coordination of discrete shunt devices such as condensers and reactors so that the reserves can avoid voltage collapse in emergency state in Jeju system. Field tests in the automatic mode of VMS operation are included in steady-states and transient states. Finally, by the successful operation of VMS in Jeju power system, the VMS is proved to effectively control system voltage profiles in steady-state condition, increase system MVAR reserves and improve system reliability for pre- and post-contingency.

• KEPCO Journal on Electric Power and Energy
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• 제3권1호
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• pp.17-21
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• 2017

Recently, the Korea Enhanced Power system Simulator (KEPS) was upgraded with new processor cards and various peripheral devices. The purpose of the upgrade is for the large-scale AC/DC simulation studies for different purposes such as FACTS, PMU applications, and SPS. The need for such study is now growing in KEPCO network. Frequently, traditional ways of performing the necessary study had been found to be less adequate for guiding the key decisions in the company. Therefore, the growing needs, as well as the revealed inadequacy of the traditional system studies, had been attributing to the momentum for the upgrade project. This paper explains the details of the upgrade project. As an example of presenting the effectiveness of the upgraded RTDS system in KEPRI-KEPCO, a large-scale AC/DC real time simulation case which includes the entire Korean network and a planned MMC-HVDC system is introduced.

• 전기학회논문지
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• 제60권5호
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• pp.921-928
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• 2011

This paper presents a new method of local voltage control to achieve coordinative control among UPFC(Unified Power Flow Controller) and conventional reactive compensation equipments, such as switched-shunt and ULTC(Under-Load Tap Changing) transformer. Reactive power control has various difficult aspects to control because of difficulty of system analysis. Recently, the progress of power electronics technologies has lead to commercial availability of several FACTS(Flexible AC Transmission System) devices. The UPFC(Unified Power Flow Controller) simultaneously allows the independent control of active and reactive power flows as well as control of the voltage profile. When conventional reactive power sources and UPFC are used to control system voltage, the UPFC reacts to the voltage deviation faster than the conventional reactive power sources. Keeping reactive power reserve in an UPFC during steady-state operation is always needed to provide reactive power requirements during emergencies. Therefore, coordination control among UPFC and conventional reactive power sources is needed. This paper describe the method to keep or control the voltage of power system of local area and to manege reactive power reserve using PSS/E with Python. The result of simulation shows that the proposed method can control the local bus voltage within the given voltage limit and manege reactive power reserve.

• 영어어문교육
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• 제10권3호
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• pp.89-112
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• 2004

This article examines the ways in which language can be exploited in the manipulation of the reader's interpretation of a text to make him/her take certain lines of thought according to the writer's persuasive intents. Such functions of language provide valid foundations to support the teaching of critical reading skills and to explore an adequate approach to discourse analysis. A pilot study was conducted to find out the extent to which the reader can be coaxed into thinking in some fashions guided by specific linguistic devices employed for ideological texts. Forty-seven subjects divided into two groups (humanities majors and natural science majors at undergraduate level) joined the two-fold questionnaire surveys intended to look at their critical reading abilities. The empirical results indicate that college students whose majors are humanities were more inclined to take a holistic approach in processing commercial advertisement texts and their abilities for critical interpretation appeared to be lower than those of the subjects whose majors are natural sciences, who showed a relatively high tendency to take an analytical approach in decoding the textual facts. As a consequence, pedagogic implications for increasing critical reading abilities have resulted in a set of analytical procedures concerning ideological texts which is linked with instructional guidelines to emphasize the importance of the reader's logical and analytical reasoning power, entirely accepted as a general prerequisite for cracking the covert language gambits.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.3-9
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• 2008

Recently, the plant industries are being activated and plant control systems use various technologies. Because the optimized design for the plants is very important for the reducing of operation and maintenance costs, automatic control systems become more important. Plant control systems consist of the master controller, the plant networks, the programming environment for engineering, monitoring software and the field devices. The control systems should have reliability, availability and safety. Modular architecture of hardware and software makes flexible configuration of the control systems. Each component should have diagnostic functions. It follows industrial standards and makes open systems. Open systems increase accessibility against the data which is distributed in the plants. The controllers including processor and communication modules use the up-to-date technology. They have real time and fault tolerant function by duplicating processors or networks. It also enables to make the distributed control systems. The distributed architecture makes more scalable main control system. Automatic control systems can be operated with better performance. In this paper, we analyzed the requirements of the seawater desalination plants and made some consideration facts for developing the optimized controller. Also we described the design concept of the main controller, which consists of several modules. We should validate and complement the design for the reliability and better performance.

• 대한간호학회지
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• 제38권3호
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• pp.353-362
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• 2008

Purpose: This study was conducted to analyze and clarify the meaning of the concept for relocation stress -focusing on patients transferred from an intensive care unit to a general ward. Methods: This study used Walker and Avant's process of concept analysis. Results: Relocation stress can be defined by these attributes as follows: 1) involuntary decision about relocation, 2) moving from a familiar and safe environment to an unfamiliar one, 3) broken relationship of safety and familiarity, 4) physiological and psychosocial change after relocation. The antecedents of relocation stress consisted of these facts: 1) preparation degrees of transfer from the intensive care unit to a general ward, 2) pertinence of the information related to the transfer process, 3) change of major caregivers, 4) change in numbers of monitoring devices, 5) change in the level of self-care. There are consequences occurring as a result of relocation stress: 1) decrease in patients' quality of life, 2) decrease in coping capacity, 3) loss of control. Conclusion: Relocation stress is a core concept in intensive nursing care. Using this concept will contribute to continuity of intensive nursing care.

• 대한한의진단학회지
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• 제16권1호
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• pp.1-8
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• 2012

Objectives Although the faith that pulse diagnosis via a thread, namely "Xuanxizhenmai", had been applied to some women in royal families, is widely spread in East Asian countries, but it is still controversial that whether this faith is based on historical facts or just originated from some folk tales. So we provided some reasonable clues to interpret that faith. Methods The digitalized Annals of Joseon Dynasty and Twenty Five Books of Chinese History were used for historical example search. Conventional internet search engines are widely used for investigation of other examples and related interpretations. Additionally, a pilot observation with nylon threads and optical vibration detection devices was performed to confirm it's feasibility. Results Although there are a few evidences supporting Xuanxizhenmai's existence in Qing dynasty, no evidence was found to show it's existence in authoritative annals of Korea and China. The pilot observation showed that in optimal environment, some intense arterial pulse could be propagated dozens of centimeter, but it was not applicable to clinical needs. Conclusions Pulse propagation via a thread was proved to be reproducible within limited extents, but pulse diagnosis via a thread, namely Xuanxizhenmai, seem to have never been used for proper clinical purpose.