• 전기학회논문지
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• 제58권7호
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• pp.1255-1262
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• 2009

The present study explained the phenomenon that low frequency oscillation is synchronized with discrete data obtained from a wide area system, and a sync search method. When a disturbance occurs in an power system, various controllers operate in order to maintain synchronization. If the system's damping is poor, low frequency oscillations continue for a long time and the oscillations are synchronized with one another at specific frequency. The present study estimated dominant modes, magnitude and phase of signals by applying parameter estimation methods to discrete signals obtained from an power system, and performed sync search among wide area signals by comparing the estimated data. Sync search was performed by selecting those with the same frequency and damping constant from dominant oscillation modes included in a large number of signals, and comparing their magnitude and phase. In addition, we defined sync indexes in order to indicate the degree of sync between areas in a wide area system. Furthermore, we proposed a wide area sync search method by normalizing mode magnitude in discrete data obtained from critical generator of the wide area. By applying the sync search method and sync indexes proposed in this study to two area systems, we demonstrated that sync scanning can be performed for discrete signals obtained from power systems.

• 전기학회논문지
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• 제61권3호
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• pp.384-393
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• 2012

Railroad signaling systems perform controlling the distance and routes between trains. Signaling methods on the wayside are to control passively the train speed by using signal flags which are installed on the wayside. ATS(Automatic Train Stop) device is used as the signaling method on the wayside in Korea. The ATS device is assistance equipment of engineers. Signal information is transmitted by combining mutual inductance between the wayside transmitter and on-board receiver. The wayside transmitter performs changing oscillation frequency according to the signal information. The on-board receiver performs controlling the train by receiving the frequency. Currently, the oscillation frequency on the on-board receiver is 78[kHz] in case of normal state. When the on-board receiver is over the wayside transmitter, the oscillation frequency is changed by capacitors of the wayside transmitter according to signal flags. In case of changing the oscillation frequency, the waveform is modified in the wayside transmitter and on-board receiver. This phenomenon is that other signals or communication frequency are included. In this paper, electric model between the wayside transmitter and on-board receiver is suggested and frequency response in the wayside transmitter and on-board receiver including other signals is estimated by the coupling coefficient. Also, the value of coupling coefficient is proposed to exclude other signals and demonstrated by using Matlab and PSpice program.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.376-379
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• 2004

The purpose of this work is to develop an effective active control system for combustion instabilities of premixed combustors. For the first step, the natural modes of combustion oscillation were investigated for a methane-air premixed combustor and the controls by secondary fuel injection were examined. The main premixed flame is stabilized by a swirler with orifices for secondary injection installed on the central hub. For sensing purposes, a pressure transducer and a chemiluminescence sensor were placed on the appropriate positions. The acoustic characteristics and the source of the oscillation were analyzed by those signals. To test the controllability, two methods of actuations by secondary fuel injection were examined. One is the open loop control and the other is the closed loop control. The comparison of the reduction levels of p $_{rms}$ shows that the closed loop control with a phase-shift injection performs best in this condition.ition.n.

• KEPCO Journal on Electric Power and Energy
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• 제6권3호
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• pp.245-252
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• 2020

It is very important to evaluate on/off-line stability to operate the power system stably and economically. Until now, we have continuously secured the operation reliability of the power system through the evaluation of transient, voltage and small signal stability. This paper proposes that it is possible to operate in KWAMS by applying the multi-section analysis and subspace methods and verifying the reliability of the algorithms to directly estimate the dominant oscillation mode of the power system from the signal waveform acquired from the phasor measurement units. In addition, this paper shows that the dominant oscillation mode can be detected from real-time measurement data in power systems. Therefore, if we can monitor the state of the power system in real time, it is possible to avoid a large-scale power outage by knowing the possibility of the power system accident in advance.

• 전기학회논문지
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• 제56권12호
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• pp.2240-2246
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• 2007

Optically coupled linear isolation amplifier requires special care to avoid oscillation in actual applications. In this paper methods to analyze the frequency characteristics of the amplifier are proposed to reveal the cause of oscillation and to provide design guidelines. The loop gain of the amplifier obtained through the equivalent circuit model shows that the phase margin is too small to ensure stable operations. Methods to get non-oscillatory response are proposed and the resulting frequency responses are analyzed. The common method adding a small capacitor to the amplifier is shown to degrade the frequency bandwidth. The frequency response of output voltage explains the need of filter capacitor in output stage. The usefulness of the method is verified through experiments.

• 한국수산과학회지
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• 제27권6호
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• pp.782-786
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• 1994

Dey and Morrison (1979)이 육상의 전기탐사문제의 해결에 성공적으로 적용한 적분차분법(integral finite different method)의 해양에서의 응용성을 연구해보기 위해, 해석해가 존재하는 연안역의 해수고유진동 문제를 도출하여 기존의 고유진동문제에 적용하여 보았다. 그 응용성의 평가는 기존 해양에 널리 적용되는 기존차분법(conventional finite different method)으로 구한 수치결과와 적분차분법으로 구한 결과를 해석해와의 비교검증을 통하여 실시되었다. 그 결과 적분차분법으로 구한 고유치와 고유함수값이 기존차분법으로 구한 결과보다 좋은것으로 나타났다. 이러한 결과는 적분차분법의 경우 원래의 기본방정식에 Green's theorem을 적용함으로써, 기본방정식에 존재하는 2계 미분연산자가 1계 미분연산자로 해석적으로 처리되었기 때문으로 사료된다. 따라서 적분차분법을 이용하여 해수고유진동문제를 비롯한 다른 유사문제를 풀 경우 기본차분법보다 좋은 결과가 나을 것으로 사료된다. 또한 미분방정식의 수치해를 구할 경우 적분법이 차분법보다 좋은해를 줄 수 있다는 것을 증명한 것으로 사료된다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제27회 추계학술대회논문집
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• pp.363-366
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• 2006

본 연구에서는 초음속 공동유동장에서 발생하는 압력 진동을 완화시키기 위하여 사용된 두 가지 피동제어방법들의 유효성을 수치해석적으로 조사하였다. 사용된 제어 장치들은 삼각돌기와 sub-cavity로, 전단층의 발달 특성을 조절하기 위하여 공동 전단 부근에 설치된다. 공동유동의 압력변동 특성을 조사하기 위하여 3차원 비정상 Navier-Stokes 방정식에 유한체적법을 적용하여 유동장을 모사하였으며, 유동의 난류상태량들은 LES 방법을 사용하여 계산하였다. 그 결과, 공동유동의 진동 특성은 공동의 후단 벽면에서 발생하는 압력 진동에 의해 지배되며, 제시된 방법들의 효과는 공동의 후단에서 가장 크게 나타났다. 특히, sub-cavity는 삼각돌기나 블로잉이 있는 경우에 비하여 압력 진동 저감효과가 상대적으로 크며, sub-cavity가 큰 경우 압력 진동의 저감효과가 더욱 뚜렷하게 나타났다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.53-58
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• 2006

Today, harbor oscillation problems are the most significant factor to consider when designing harbors serving very large ships. In coastal harbors, large vessels moored in the elastic hawsers are often displaced due to the resonance between long period waves and mooring systems. As a result, cargo handling may be interrupted and the hawsers may be broken, especially when the amplification becomes extreme. The most significant harbor confronted with harbor oscillation problem in Korea is Pohang New port. Many cases of problems are being reported by the pilot association and the local office of MOMAF (Ministry of Maritime Affairs and Fisheries). However, it is difficult to prevent the arrival of long waves causing oscillation within this harbor. Moreover, the Korean government has already started a new port plan at the mouth of Yeongil Bay without addressing the problems that have occurred in Pohang New port. This study deals with the variation of harbor oscillation due to the construction of a 4.1 km breakwater at the bay mouth including the arrangement of the new berths. Numerical methods used are in fairly standard form from the extended mile slope equation. The obtained numerical results were compared with field measurement from the previous and this will bring a certain level of discussion and consideration of variation to the future port development.

• 전기전자학회논문지
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• 제26권4호
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• pp.553-559
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• 2022

본 논문에서는 cascode GaN FET의 하프 브릿지 구성에서 오실레이션 억제를 위한 RC 스너버 회로 설계 기술을 분석한다. 대표적인 WBG 소자인 cascode GaN FET는 우수한 고속 스위칭 특성이 우수하다. 다만, 이러한 고속 스위칭 특성으로 인하여 false turn-off 문제가 야기되며, 이를 억제하기 위해 RC 스너버 회로가 필수적이다. 따라서, 일반적으로 많이 사용되는 실험 기반의 선정 기법과 근궤적법을 이용한 분석 기법을 비교한다. 일반적인 방법의 경우 실험적 경험을 바탕으로 오실레이션 억제 성능이 만족될 때까지 지속적인 회로 변경이 필요하다. 하지만, 근궤적 기법의 경우 비진동 R-C 맵을 기반으로 초기값을 설정 할 수 있다. 이러한 설계 기술에 따른 성능을 비교하기 위해 모의실험과 실제 더블 펄스 회로 구성을 통한 실험을 진행하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제25회 추계학술대회논문집
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• pp.117-120
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• 2005

본 연구에서는 초음속 공동 주위에서 발생하는 비정상 유동현상을 이해하고, 공동시스템이 설치된 장치의 성능 및 안정적인 운전을 방해할 수 있는 공동유동의 압력진동을 제어할 수 있는 방법을 제시한다. 사각형의 공동을 지나는 초음속 유동장은 3차원 비정상 압축성 Wavier-Stokes 방정식에 완전 내제적 유한체적법 및 large eddy simulation을 적용하여 수치모사하였다. 수치계산은 공동전단 근처에 설치된 삼각돌기나 블로잉 제트가 초음속 공동유동장의 유동특성에 미치는 영향을 조사하였다. 본 수치계산 결과로부터 이러한 제어방법들이 특히 공동후단 부근에서 발생하는 강한 압력진동을 억제하는데 효과가 있음을 알 수 있다.