• 한국전기전자재료학회논문지
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• 제35권6호
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• pp.568-575
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• 2022

This paper is a study on frequency analysis and electronic noise reduction of energy storage system (ESS). We acquired 4 necessary data for about 2 minutes and 4 seconds using a sampling frequency of 10,000 Hz in ESS. Fast Fourier transform (FFT) was used for electronic noise analysis from the acquired data. As a result, it was confirmed that DC component, fundamental wave, second and higher harmonic component exist. For the attenuation of harmonics, low-pass filter (LPF) was applied. We confirmed that an attenuation of approximately 59.3% appears from the second harmonic. The presence of many harmonic components in the data of the ESS was expected to occur due to the insufficiency of optimization among the modules inside the ESS. Therefore, we propose that a national certification system for ESS should be introduced to settle down the issue properly.

• Journal of the Optical Society of Korea
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• 제7권3호
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• pp.131-134
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• 2003

We demonstrated an optical frequency synthesizer based on a femtosecond (fs) mode-locked Ti:sapphire (Ti:s) laser by simultaneously stabilizing the carrier-offset frequency, $f_{ceo}$, and repetition rate, $f_{ rep}$, referenced to the Cs atomic frequency standard. By using two wide-band digital phase-detectors we realized a phase-coherent link between $f_{rep} and f_{ceo} with the relation f_{ceo} = f_{AOM} 5/6f_{rep} ≡ 0, where f_{AOM} = 5/6f_{rep}$ is the phase-locked driving frequency of an acousto-optic modulator (AOM) in a self-referencing interferometer and $f_{rep}$ = 100 MHz. As a result, we could stabilize all components of the fs laser comb at once with an equal frequency separation $f_{rep}$ = 100 MHz with $f_{ceo}$ = 0. In our optical frequency synthesizer, the frequency of the nth component ($f_{n}$) is given exactly by the simple relation $f_n = nf_{rep}$, enabling us to use the fs laser comb as a frequency ruler in the optical frequency metrology.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 A
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• pp.211-213
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• 2005

In this paper, the frequency compensator for digital protective relay is introduced. Due to sudden appearance of generation-load or fault in power system, the frequency can deviate from its nominal value. The Orthogonal filter adopted to digital protective relay is exposed to the problem. Therefore, the frequency variation makes a difficult to protective function and power measurement in digital protective relay. The essential property of the proposed algorithm presented is its outstanding immunity to both signal orthogonal component magnitudes and DFT filter gain variations which ensures below 0.05Hz accuracy of estimation. Additionally, the proposed method has excellent characteristics with low signal sampling rate. Based on the frequency estimation, author design under frequency protection relay for generator and verifies its performance with several experimental tests.

• KIEE International Transactions on Electrophysics and Applications
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• 제2C권5호
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• pp.273-278
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• 2002

Even though the modulating signal frequency of the light is too high to detect directly, the signal can be extracted by frequency conversion at the same time as the detection by means of the non-linearity of the APD. An analysis is presented for super-high-speed optical demodulation by an APD with electronic mixing. A normalized gain is defined to evaluate the performance of the frequency conversion demodulation. The nonlinear effect of the internal capacitance was included in the small signal circuit analysis. We showed theoretically and experimentally that the normalized gain is dependent on the down converted difference frequency component. In the experiment, the down converted different frequency outputs became larger than the directly detected original signal for the applied local signal of 20㏈m.

• 음성과학
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• 제8권4호
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• pp.45-58
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• 2001

Modulated components of a speech signal are frequently used for speech coding, speech recognition, and speech synthesis. Time-frequency representation (TFR) reveals some information about instantaneous frequency, instantaneous bandwidth and boundary of each component of the considering speech signal. In many cases, the extraction of AM-FM components corresponding to instantaneous frequencies is difficult since the Fourier spectra of the components with time-varying instantaneous frequency are overlapped each other in Fourier frequency domain. In this paper, an efficient method decomposing speech signal into AM-FM components is proposed. A variable bandwidth filter is developed for the decomposition of speech signals with time-varying instantaneous frequencies. The variable bandwidth filter can extract AM-FM components of a speech signal whose TFRs are not overlapped in timefrequency domain. Also, amplitude and instantaneous frequency of the decomposed components are estimated by using Hilbert transform.

• 대한전기학회논문지:전력기술부문A
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• 제53권8호
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• pp.432-437
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• 2004

Since the characteristic frequency is decreased in proportion to the fault distance, the characteristic frequency component may be insufficiently eliminated by a low-pass filter on a long transmission line. In order to set a standard for the cut-off frequency of the low-pass filter, this paper proposes a method for obtaining the characteristic frequencies due to line faults. The application results of the proposed method are presented for line to ground (LG) faults and line to line (LL) faults on a 345 kV 200 km overhead transmission line. The EMTP is used to generate fault signals under different fault locations and fault inception angles. By comparison between the characteristic frequencies obtained from the proposed method and the EMTP simulation, it is shown that the proposed method accurately obtains the characteristic frequency.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1791-1793
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• 2003

In order to analyze the dynamic characteristics of ground impedance in large grounding system for lightning and surge protections, a novel method for measuring the ground impedance as a function of frequency was proposed. The experiments were carried out in the grounding system composed of ground rods and mesh grids. The test current was injected by the variable frequency inverter whose frequency is linearly controlled in the range of $5{\sim}500$kHz. The ground impedance and frequency response of the grounding system were mainly caused by the inductive current flowing through grounding conductors over the frequency of 2002. In the combined grounding system of rods and mesh grids, inductive component of ground impedance was significantly decreased. It was fumed out that the grounding system is effective for the surge protection.

• 대한전자공학회논문지TC
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• 제42권1호`
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• pp.1-8
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• 2005

본 논문에서는 채널간간섭 자기소거를 위한 부대역 부호화기법에 따른 직교 주파수분할다중화의 첨두전력 대 평균전력비가 분석된다. 인접부대역에 대척신호를 할당하는 기존 상관부호화의 경우 전송신호열에서 형상성분이 발생됨을 이론적ㆍ실험적으로 검증한다. 이로 인하여 심볼의 중간부분과 가장자리부분에서의 신호전력은 서로 다른 가중치의 영향을 받게 되며, 이는 증가된 첨두전력 대 평균전력비를 초래한다. 이와 같은 문제점을 극복하기 위하여 본 논문에서는 새로운 간단한 부대역 부호화기법이 제시된다. 여기서는 신호쌍의 위상차가 매 신호마다 변화되도록 할당함으로써 신호의 부분적인 반복성으로 인한 형상성분을 제거한다. 그 결과, 새로운 부대역 부호화기법이 적용된 시스템은 기존의 시스템보다 2～3 dB 적은 첨두전력 대 평균전력비를 가지면서도 일반적인 직교 주파수분할다중화에 비하여 현저히 큰 반송파대 간섭비를 유지한다.

• 한국음향학회지
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• 제38권6호
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• pp.687-696
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• 2019

기존의 지진파 분류 특징은 강진에 초점이 맞추어져 있어서 미소지진과 같은 지진파는 다소 적합하지 않다. 본 연구에서는 강진과 더불어 미소지진, 인공지진, 잡음 분류에 적합한 특징 추출을 위해 주파수-시간 공간 내에서 히스토그램과 주성분 기반 특징 추출방법을 제안한다. 제안된 방법은 지진파의 주파수 관련 정보와 시간 관련 정보를 결합하는 방법을 적용한 히스토그램 기반 특징 추출방법과 주성분 기반 특징 추출방법을 이용하여 지진(강진, 미소지진, 인공지진)과 잡음, 미소지진과 잡음, 미소지진과 인공지진을 이진 분류한다. 2017년~2018년 최근 국내지진 자료와 분류 성능을 토대로 제안한 특징 추출방식의 효용성을 비교 평가한다.

• 한국통신학회논문지
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• 제40권2호
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• pp.298-306
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• 2015

본 논문에서는 위성/지상 겸용 망에서 위성 망과 지상 망간 주파수를 효율적으로 공유할 수 있도록 기여하는 최적의 자원 할당 방식에 대한 성능을 비교 분석한다. 제안된 방식은 동일한 주파수를 사용하는 위성 빔과 인접 빔 내 지상 셀 시스템 간 발생할 수 있는 간섭을 경감시킴과 동시에 망 내 발생한 트래픽 요구량을 만족시키기 위해 필요한 전력을 최적화하여 주파수 자원 이용 효율을 향상시킬 수 있다. 이와 같은 겸용 망에서는 각 시스템 간 상이한 트래픽 환경 및 업/하향링크 환경에 따라 주파수를 공유하는 위성과 지상 시스템 간 간섭 환경이 달라질 수 있다. 따라서 본 논문에서는 위성/지상 겸용 망에서의 업/하향링크 환경을 가정한 성능을 비교 분석함으로써 보다 실제 통신 환경에서의 제안된 알고리즘에 대한 성능의 우수성을 보인다.