• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1699-1700
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• 2006

본 논문에서는 1kVA급 비선형 부하에서 발생한 고조파 전류의 저감을 위한 시스템을 설계 및 제작하였다. 제안된 시스템은 비선형 부하의 차수별($3{\sim}9$차) 고조파 발생량을 검출한 후 설정된 기준치를 넘어서는 고조파들을 저감할 수 있도록 해당하는 고조파의 수동 필터만 스위치를 이용하여 연결하는 구조를 가진다. 스위칭을 위한 제어기는 아날로그 소자만으로 구성되어 있다. 제안된 방법은 기존 수동 필터의 다양한 비선형 부하에 적용되지 못하는 단점을 보완하는 동시에 능동 필터보다 단순하며 저가로 구현할 수 있다. 형광등 부하와 다이오드 정류 부하이 대한 실험을 통해 제안된 시스템의 성능과 타당성을 입증하였다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.5
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• pp.59-63
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• 2011

We present a lattice transversal joint (LTJ) adaptive filter with fixed reflection coefficients to achieve fast convergence with low complexity. The reflection coefficients of the filter are given by the statistics of speech signals, and the proposed order of the lattice predictor is one. Experimental results confirm that as compared to the adaptive transversal filter, the proposed adaptive filter achieves fast convergence with a negligible increase in complexity. The proposed adaptive filter converges around six times faster than the adaptive transversal filter in case of the band-limited voiced signal from the ITU-T G.168 standard.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.7C
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• pp.451-458
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• 2011

Maximally flat (MAXFLAT) FIR filter design provides the advantage of giving a closed-form solution, but there still remains a problem of exactly and efficiently choosing the order of flatness for the accurate design of filters. This paper provides, through the modeling and analysis of a frequency-domain error function in the closed-form solution, how to determine the order of flatness. A proposed method, based on the frequency-domain error function, is accomplished by computing a minimum distance between its peak frequency and specified cutoff frequency. It is also shown that the proposed scheme is computationally efficient and accurate than the empirical formula given by Herrmann.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.121-131
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• 2008

In constructing a slurry trench cutoff wall, bentonite-water slurry is used to secure the stability of sidewalls during excavation before the wall is completed by backfilling. Unexpectedly, a thin but relatively impermeable layer called filter cake can be formed on the excavation surface, which significantly influences the result of slug test analysis in the cutoff wall if not considered. This study is to examine the effect of filter cake on evaluating hydraulic conductivity of the vertical cutoff wall through slug test analysis with the aid of the verified numerical program Slug_3D. The no-flux boundary conditions were adopted in Slug_3D to simulate the filter cake on the interface between the wall and the natural soil. A new set of type curves were built for applying the type curve method. New modification factors were obtained for using the modified line-fitting method. With consideration of filter cake, the type curve method and the modified line-fitting method were adopted to reanalyze the case study taken from EMCON (1995). The previous results achieved by Choi and Daniel (2006) without consideration of filter cake were compared with the present results obtained in this paper. The comparison emphasizes the necessity of considering filter cake when analyzing slug test results in vertical cutoff walls.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.3
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• pp.105-112
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• 2007

In general, the earlier methods for the design of MAXFLAT FIR filters have existent problems due to the approximation algorithms used to approach MAXFLAT(maximally flat) response in the passband and the stopband.. The proposed approach advanced by using of MAXSHCUT(maximally sharp cutoff) condition in this paper clearly overcomes these problems. In this approach, we use a key parameter represented with filter-order and cutoff-frequency parameters for obtaining the lowpass filters with the MAXFLAT and MAXSHCUT characteristics in the frequency domain. Consequently, this design technique leads to new MAXFLAT and MAXSHCUT FIR digital filter, which can achieve sharp-cutoff responses with the stopband attenuation exceeding 100 dB almost everywhere.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.150-155
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• 2014

본 논문에서는, 원거리 음성인식을 위한 서브밴드 필터링 기반의 빠르고 효율적인 에코제거 시스템을 제안한다. 제안하는 에코제거 시스템은 우선 채널간 유사도 (correlation) 가 높을 경우 적응필터가 오작동하는 것을 방지하기 위해 spatial decorrelation 을 적용하게 된다. 그리고 tree 형태를 가지는 IIR filterbank 기반의 subband 구조를 채택함으로써, 적은 차수로도 효과적인 analysis, synthesis 필터링을 수행할 수 있도록 한다. 이 과정에서 불가피하게 발생하는 서브 밴드간 spectral aliasing은 notch filter를 적용해 해결할 수 있다. 또한 적응 필터로는 improved proportionate normalized least-mean-square (IP-NLMS) 알고리즘을 사용해 수렴속도 및 에코제거 성능에서 우수함을 확인하였다. 마지막으로 decision-directed estimation 기반의 residual echo suppressor를 적용해 잔여 에코를 제거하게 된다. 본 논문에서는 각 단계를 구성하게 된 이론적인 배경을 소개하고, 실제 에코가 존재하는 환경에서 ERLE, 원거리 음성 인식률, computational complexity를 통해 제안하는 에코제거 시스템의 효과를 입증하도록 한다.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.1
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• pp.150-158
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• 2010

Filtering is necessary for the SRC(sample rate converter), that is used to change the sampling rate of a digital signal. The larger the conversion ratio of the sampling rate becomes, the more signal processing is needed for the filter, which means more complexity on realization. Thus it is important to reduce the amount of signal processing for the case of substantial conversion ratios. In this paper it is presented an efficient design method of a multistage FIR(finite impulse response) filter, with which the rate conversion occurs in stages rather than in one step. In this method, filter searching is performed exhaustively over all possible factorization of the conversion ratio, and also the filter complexity is measured based on direct realization rather than on estimation. It has been shown a designed multistage filter to have a less number of multiplications for filtering operation in comparison with a conventionally designed one. It has also been found that by allowing some variations of the filter architecture such as a halfband filter or a filter with multiple transition bands, the number of multiplications can be reduced further.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.898-899
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• 2008

본 논문에서는 3상 정류기부하에서 주로 발생하는 5차, 7차등의 저차 고조파를 제거하기 위하여 간단한 구조와 경제성이 있는 Single-tuned Second-order Filter를 설계하였다. 사례연구는 원자력발전소 무정전전원계통(UPS)의 임의의 한 모선을 대상으로 하였으며 계통을 모델링하여 분석한 결과를 토대로 수동필터를 설계하였다. 설계된 필터는 범용 컴퓨터프로그램인 PSIM을 이용하여 시뮬레이션을 수행하였으며 시뮬레이션 결과 해당차수의 고조파를 현저하게 감소시키는 양호한 결과를 얻었다.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.207-208
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• 2015

최근 HVDC의 설치가 증가하면서 HVDC 컨버터에 의한 고조파가 계통에 영향을 끼치고 있다. 고조파는 전압 왜곡, 손실 증가, 과열 등의 문제를 야기하므로 고조파 필터를 통해 제거되어야 한다. 효율적인 고조파 필터 설계를 위해서는 계통의 고조파 임피던스에 대한 분석이 필요하다. 본 논문에서는 PSS/E에 내장된 IPLAN 프로그램을 사용하여 계통의 고조파 임피던스 특성을 분석하였다. 계통 요소의 모델링은 집중 부하모델 4와 과도 리액턴스 발전기 모델을 사용하였다. 중첩 원리를 이용하여 PSS/E에 내장된 IEEE 25모선에서 1차 고조파에서 70차 고조파까지의 고조파 차수 변화에 대한 계통 임피던스를 계산하였다.

• Journal of Biomedical Engineering Research
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• v.10 no.2
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• pp.151-156
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• 1989

Lung sound analyer which can provide an objective diagnosis of patients with pulmonary and bronchial disorders is designed. For the purpose of power spectrum analysis, adaptive digital filtering technique and TM - S320C25 DSP chip is used. As a results, adaptive lattice Wiener filter could eliminate heart sounds with a few of 10th order and on the distribution of power spectrum each patterns has shown in normal vescicular breathy from 100 Hz to 200 Hz, in crackle sound from 100 Hz to 400 Hz, in wheeze sound from 150 Hz to 600 Hz.