• Journal of Power Electronics
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• 제11권3호
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• pp.304-310
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• 2011

The power series approximation method is proposed for real time implementations of a discrete flux observer. The proposed method improves the performance of the discrete flux observer in the case of a low sampling rate and high speed range, where the simple discrete flux observer converted by the Euler method cannot estimate the actual flux precisely. The performance of discrete flux observers with different orders of approximation is compared to find out the proper order of approximation. The validity of the proposed method is verified through simulation and experiment.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 춘계학술대회 논문집 센서 박막재료연구회 및 광주 전남지부
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• pp.98-102
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• 2008

Methods and analysis of a simple wireless sensor concept for detecting and locating faults as well as for load monitoring are presented. The concept is based on distributed wireless sensors that are attached to the incoming and outgoing power lines of secondary substations. A sensor measures only phase current characteristics of the wire it is attached to, is not synchronized to other sensors and does not need configuration of triggering levels. The main novelty of the concept is in detecting and locating faults by combining power distribution network characteristics on system level with low power sampling methods for individual sensors. This concept enables the sensor design to be simple, energy efficient and thus applicable in new installations and for retrofit purposes in both overhead and underground electrical distribution systems.

• 소음진동
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• 제5권1호
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• pp.37-48
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• 1995

The prediction of sound pressure using acoustic holography has been recognized as a useful tool for the visualization of sound field. Cylindrical acoustic holography amongst acoustic holographic methods planar, spherical, and cylindrical ones-has a wide range of application since its rather simple construction and easy implementation for the sources. To utilize the propery of cylindrical holographic method, estimation errors associated with holographic parameters such as aperture size and sampling space must be envisaged. In this these errors have been studied by numerical simulation and the relation between the errors and the spectrum in wavenumber domain is described. The results are also confirmed by simple experiments.

• 전자공학회논문지SC
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• 제44권6호
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• pp.57-65
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• 2007

본 논문에서는 DSP(TMS320F2812)를 사용하여 단상 역률개선을 디지털로 설계하였다. 이러한 승압형 역률개선 컨버터를 디지털로 구현하기 위하여 DSP는 컨버터의 입력전압과 인덕터전류, 컨버터의 출력전압이 필요하며 이를 DSP 내부에 있는 12비트 A/D변환기로 구현하였다. 승압을 위한 스위칭소자인 FET가 ON/OFF 될 때 심한 고주파 노이즈와 스위칭 리플이 발생한다. DSP에 의해 구현시 어느 시점에서 A/D 변환을 시작할지 결정하는 것은 대단히 중요하며 스위칭 노이즈가 발생하지 않는 곳에서 A/D 변환을 할 필요가 있다. PWM의 시비율(duty ratio)은 약 5 %에서 95 %까지 가변적이기 때문에 A/D 변환의 고정된 시작점을 찾을 수는 없다. 따라서 본 논문에서는 25 us 마다 PWM의 ON/OFF 폭을 미리 예측한 후 타이머를 이용하여 A/D 변환을 하도록 하였다. 실험 결과들로부터 광범위한 입력전압에 대하여 약 0.99의 역률과 80 Vdc 출력 전압에 대한 리플이 약 5 Vpp임을 확인하였다. 또한 윈도우즈 Xp 환경 하에서 수행되는 응용프로그램을 작성하여 원격에서 단상 PFC 컨버터의 각종 파라미터들과 전압 및 전류 제어기의 이득들을 모니터링하며 원격제어가 가능함을 보여 상용화의 가능성과 유용성을 제시하였다.

• 한국수자원학회논문집
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• 제44권4호
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• pp.295-304
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• 2011

효과적인 수질관리를 위해서는 수질정보의 기대수준에 맞는 신뢰성 있는 수질자료가 확보되어야 한다. 이런 점에서 볼 때 수질모니터링은 조사지점, 수질항목, 측정주기 등이 성패의 중요한 요인이 되며, 이중에서 특히 조사지점은 가장 중요한 사항으로 판단된다. 그러나 지금까지 수질조사를 위한 관측지점은 대부분 정성적 판단에 따라 정해지고 있었기 때문에 수질 대표성이 문제가 되기도 하였다. 본 논문에서는 이와같은 수질측정망 구축 시 문제점을 과학적인 통계기법을 적용하여 개선한최적수질측정망구축시스템으로제시하였다. 구축된 최적수질측정망 구축시스템은 SAS 프로그램 버전 9.2를 기반으로 만들었으며, 이용자의사용편의성을 고려하여 간단한 입력으로 측정망을 구축할 수 있는 체계로 구성하였다. 분석 데이 터형식은 자료 입출력 및 관리가 용이한 엑셀데이터를 사용하도록 하였으며, 관측지점별 데이터는 시트로만 구별하게 하였다. 시스템에서는 시계열 분석과 유사성계산을 하여, 각 수질의 변화패턴을 고려할 수 있는 상관계수를 활용한 다차원척도법을 적용하여 그 결과를 덴드로그램으로 제시하며, 그 결과를 활용하여 군집 개수를 결정한다. 이용자가 최종 산점도 출력시스템에 원하는 군집의 개수를 입력하면 수질 특성 파악이 가능한 주성분 산점도가 출력되며, 군집 내 관측지점의 중심점을 대표지점으로 선정하면 된다.

• 한국산업보건학회지
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• 제4권2호
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• pp.208-223
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• 1994

The purpose of this study was to evaluate the efficiency of diffusive(or passive) sampler in measuring airbone organic solvents. Diffusive samplers are generally simple in construction and do not require power for operation. The efficiency of the diffusive samplers has not sufficiently been investigated in Korea. Three types of samplers were studied in this study. The sampling and analytical results by passive samplers were compared with results by charcoal tube method recommended by NIOSH(National Institute for Occupational Safty and Health). The following characteristics are identified and studied as critical to the performance passive monitors; recovery, reverse diffusion, storage stability, accuracy and precision, face velocity and humidity, n-Hexane, TCE(trichloroethylene) and toluene were used as test vapors. A dynamic vapor exposure system consisting of organic vapor generator and sampling chamber for evaluating diffusive samplers are made. The results of the study are summarized as follows. 1. NIOSH recommands that the overall accuracy of a sampling method in the range of 0.5 to 2.0 times the occupational health standard should be ${\pm}25$ percent for 95 percent confidence level. Among three types of diffusive samplers, sampler A has permeation membrane and samplers Band C have diffusive areas, samplers A and B met the criterion that overall accuracy for 95% confidence level of the samplers were within ${\pm}25$ percent of the reference value. Sampler C had overall accuracy ${\pm}9.6%$ and ${\pm}11.8%$ in hexane and TCE, respectively. The concentration of toluene was overestimated in sampler C with overall accuracy of ${\pm}43.9%$. 2. The desorption efficiencies of diffusive samplers were 96-107%. 3. There was no significant sampe loss during four weeks of storage both with and without refrigeration. 4. There was no significant reverse diffusion, when the samplers were exposure to clean air for 2 hours after sampling for 2 hours at the level of 2 TLY. 5. In case of 8 hours sampling, relative differences(RD) of concentrations between charcoal tube method and diffusive method were 15-39%, 13-46%, and 4-35% for sampler A, B and C, respectively. The performance was poor in 8 hours sampling for multiple substance monitors. 6. At high velocity(100 cm/sec), samplers B and C overestimated the concentrations of organic vapors, and sampler A with permeation membrance gave better results. 7. At 80% relative humidity, samplers showed no siginificant effect. Low humidity also did not affect the diffusive samplers.

• 대한기계학회논문집
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• 제10권3호
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• pp.326-334
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• 1986

The effects of flow interaction between adjacent sprays in twin-spray system on the spatial distribution of injected liquid (water) and drop size distribution in condensable (steam) environment were carefully observed through experiments. The spatial distribution of injected liquid in twin-spray system appears to be more uniform than the simple superposition of the spatial distributions of liquid obtained from each individual spray. Drop size distribution was obtained by using the immersion sampling technique. It was found that, in the twin-spray, the larger numbers of small drops are collected throughout the spraying region due to the increase of entrainment velocity of ambient steam compared with the case of simple superposition of each individual spray. Moreover, in the overlapped portion of the twin-spray, the drop size distribution was changed also due to the collision between large drops. As a result, the behavior of twin-spray system (and eventually multiple-spray system) can not be predicted precisely by simple superposition of the behaviors of each constituting spray. Hence, for the design of multiple spray system, the effect of flow interaction between sprays should be taken into account seriously.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(2)
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• pp.560-564
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• 2003

This paper proposes a simple control strategy based on the discontinuous PWM(DPWM) to balance the DC-link voltage of three-level Neutral-Point-Clamped(WPC) inverters at low modulation index. New DPWM methods in multi-level inverter are also introduced. The proposed DPWM method changes the path and duration to flow the neutral point current out of or into neutral point of the DC-link and it makes the overall fluctuation of the DC-link voltage zero during a sampling time of reference voltage vector. Therefore, the voltage of the DC-link can be balanced fairly well and also the voltage ripple of the DC-link is reduced significantly. Moreover, comparing with conventional methods, the proposed strategy is very simple. The validity of the proposed DPWM method is verified by experiment

• Journal of Power Electronics
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• 제3권4호
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• pp.205-214
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• 2003

This paper proposes a simple control strategy based on the discontinuous PWM (DPWM) to balance the DC-link voltage of three-level neutral-point-clamped (NPC) inverter at low modulation index. It introduces new DPWM methods in multi-level inverter and one of them is used for balancing the DC-link voltage. The current flowing in the neutral point of the DC-link causes the fluctuation of the DC-link voltage of the NPC inverter. The proposed DPWM method changes the path and duration time of the neutral point current, which makes the overall fluctuation of the DC-link voltage zero during a sampling time of the reference voltage vector. Therefore, by using the proposed strategy, the voltage of the DC-link can be balanced fairly well and the voltage ripple of the DC-link is also reduced significantly. Moreover, comparing with conventional methods which have to perform the complicated calculation, the proposed strategy is very simple. The validity of the proposed DPWM method is verified by the experiment.

• 한국정보과학회논문지:시스템및이론
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• 제30권3_4호
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• pp.205-212
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• 2003

본 논문은 전형적인 슈퍼샘플링과 거의 동일한 수준의 고화질 영상을 생성하는 동시에, 요구되는 메모리 크기와 메모리 대역폭을 줄일 수 있는 간단하고 효율적인 하드웨어 지원 안티알리아싱 알고리즘과 렌더링 구조를 제안한다. 본 논문에서는 가장 최근에 색상 값 결정을 위해 사용된 프레그먼트의 일부분 또는 병합된 결과를 저장하는 RUF (Recently Used Fragment) 버퍼와 RUF 버퍼의 정보를 이용하여 효과적으로 색상 값을 결정하는 알고리즘을 제안한다. 제안된 방법은 데이타 구조상 샘플링 포인트 수가 늘어날수록 슈퍼샘플링에 비해 메모리 절약 효과가 크다. 또한 본 논문의 실험결과 8산개(sparse) 샘플링 포인트를 가지는 경우, 슈퍼샘플링에 비해 제안된 안티알리아싱 기법은 약 1.3%의 색상 차이를 가지나, 렌더링 과정에서 요구되는 메모리 크기가 약 31%로 감소하였으며, 실험에 사용된 3차원 모델에 대해 평균 11%의 메모리 대역폭 감소를 보인다.