• 전력전자학회논문지
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• 제27권6호
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• pp.464-470
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• 2022

A new type of soft-switching forward converter is proposed in this study. By adding only a few components, the inductor, diode, switch, and capacitor exhibit higher efficiency than the conventional forward converter. Therefore, the switching losses of the proposed forward converter are considerably reduced compared with those of the conventional forward converter. In addition, the reset winding is not used because of the capacitor employed in the auxiliary circuit. The auxiliary capacitor is adopted for zero-current-transition operation and for dissipating magnetization energy. The performance of the proposed forward converter is validated using experimental results from a 60 W, single-output, forward converter prototype, and design guidelines are presented.

• 한국안전학회지
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• 제37권1호
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• pp.12-19
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• 2022

Circuit breakers are a crucial factor in ensuring the safety of a Direct Current (DC) grid. One type of DC circuit breaker, the Z-source DC circuit breaker (ZCB), uses a thyristor, which is a type of semiconductor switch. In the event of a fault in the circuit, the ZCB isolates the fault by generating a zero crossing current in the thyristor. The thyristor quickly and actively isolates the fault while generating a zero crossing current, but thyristor switch cannot control turn-off and the allowable current is lower than the current of the mechanical switch. Therefore, it is best to use a mechanical switch with a high allowable current capacity that is capable of on/off control. Due to the slow reaction time of mechanical switches, they may not isolate the fault during the zero crossing current time interval created by the existing circuit. In this case, the zero crossing current time can be increased by using the property that hinders the rapid change in the current of the inductor. This paper will explore whether adding system inductance to increase the zero crossing current time interval is a solution to this problem. The simulation of changing inductor and capacitor (LC) of the circuit is repeated to find an optimal change in the zero crossing current time according to the LC change and provides an inductor and capacitor range optimized for a specific load. The inductor and capacitor range are expected to provide optimization information in the form LC values for future applications of ZCB's using a mechanical switch.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2008년도 하계학술대회 논문집
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• pp.523-525
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• 2008

Novel zero-voltage switching(ZVS) dual inductor-fed DC-DC converter integrating a conventional dual inductor-fed boost converter(DIFBC) and a parallel bidirectional boost converter has been proposed. Most of current-fed type boost topologies including dual inductor schemes have crucial defects such as a high voltage spike on the main switch when it comes to turning off, an unattainable soft start-up due to the limited range of duty ratio, above 50%, and considerable switching losses due to the hard switching. By adding two auxiliary switches and an output capacitor on the conventional DIFBC, the proposed circuit can solve mentioned problems and improve the efficiency with simple methods. The operational principle and theoretical analysis of the proposed converter have been included. Experimental results based on a 42V input, 400V/1A output and 50kHz prototype are shown to verify the proposed scheme.

• Journal of the Korean Data and Information Science Society
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• 제27권5호
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• pp.1225-1239
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• 2016

We investigate pediatric tumor incidence data collected by the Florida Association for Pediatric Tumor program using various models commonly used in disease mapping analysis. Particularly, we consider Poisson normal models with various conditional autoregressive structure for spatial dependence, a zero-in ated component to capture excess zero counts and a spatio-temporal model to capture spatial and temporal dependence, together. We found that intrinsic conditional autoregressive model provides the smallest Deviance Information Criterion (DIC) among the models when only spatial dependence is considered. On the other hand, adding an autoregressive structure over time decreases DIC over the model without time dependence component. We adopt weighted ranks squared error loss to identify high risk regions which provides similar results with other researchers who have worked on the same data set (e.g. Zhang et al., 2014; Wang and Rodriguez, 2014). Our results, thus, provide additional statistical support on those identied high risk regions discovered by the other researchers.

• Journal of Pharmaceutical Investigation
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• 제21권1호
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• pp.1-10
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• 1991

Hydrogels containing ketoprofen were prepared by adding NaOH or $Ca(OH)_2$ solution to Eudragit L, S and Eudispert hv at various concentration. And xerogels were prepared by drying hydrogels. On the other hand, organogels containing ketoprofen were prepared by mixing Eudragit L or S and propylene glycol. Effects of polymer content and base on drug release were investigated using KP V dissolution method. The release rate of ketoprofen from Eudragit L & S hydrogel decreased with increasing in polymer content. And the drug release rate from cal. hydroxide based gels were more decreased than that from sod. hydroxide based gels. At pH 7.2 dissolution medium, e release of ketoprofen from Edispert hv hydrogel followed apparent zero order kinetics. The release of ketoprofen from xerogel involved in simultaneous absorption of water and desorption of ketoprofen via a pH-dependant swelling controlled mechanism. The release of ketoprofen from Eudragit S organogels followed apparent zero order kinetics, providing strong evidence for a surface erosion mechanism.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.649-652
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• 2008

유리는 흔히 재활용되어 사용되는 것이 일반적이나 유리를 재활용하기 위하여 파쇄 및 분쇄하는 과정에서 유리 미분말이 발생하게 된다. 이러한 폐유리 미분말은 대부분 매립에 의존하고 있으며, 구성성분은 SiO$_2$가 73%, Al$_2$O$_3$가 16%로 중합반응에 필요한 성분이 다량으로 포함되어 있어 플라이애시보다 중합반응에 필요한 원소를 다량 포함하고 있다. 본 연구에서는 플라이애시 100% 사용 모르타르에 폐유리 미분말을 5$\sim$15% 혼합한 시멘트 ZERO 모르타르의 유동성 및 압축강도를 검토하였다. 플로우실험결과 폐유리 미분말의 혼합률은 작업성에 영향을 미치지 않는 것으로 나타났다. 압축강도 실험결과 폐유리 미분말을 5% 혼합한 경우 재령 28일 압축강도가 약 6%정도 상승하였으나 폐유리 미분말을 10% 혼합한 경우에는 기준배합과 동일하고, 15%를 혼합한 경우 약 6% 정도의 압축강도가 감소하였다. 이상의 결과를 요약하면, 폐유리 미분말을 사용할 경우 5$\sim$10%를 혼합 사용하는 것이 가장 적절할 것으로 사료된다.

• 전자공학회논문지B
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• 제33B권12호
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• pp.106-112
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• 1996

A ZVT (zero voltage transition) converter for SRM (switched reluctance motor) drives is proposed in this study. By adding a ZVT-chopping switch in the front-end, all switches in the machine side converter can be operated without any chopping to regulate phase current. This allows the use of low-cost and slow-switching devices for the machine side converter. The ZVT circuitry allows high frequency operation of th echopping switch, which enhnaces the system dynamcis and phase-current ripples. High efficiency of th eintegrated converter is obtained due to low switching losses.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2001년도 봄 학술발표회 논문집
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• pp.42-49
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• 2001

In this paper the efficient finite element for stress analysis of plane stress/strain problems is proposed. This element is achieved by adding the bubble-mode function to 8-node element. The stiffness matrix of the element is calculated by using modified numerical integration order to avoid spurious zero energy mode. In order to demonstrate the performance of this element numerical tests for various verification problems are carried out. The results of numerical tests show accuracy and reliability of the element presented in this paper.

• 조명전기설비학회논문지
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• 제19권8호
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• pp.62-69
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• 2005

본 논문에서는 보조 스위치의 하드 스위칭 문제를 개선한 AC/DC PFC(Power-Factor-Correction) ZVT(Zero-Voltage-Transition) Boost 컨버터에 관하여 논하였다. 기존의 AC/DC PFC ZVT Boost 컨버터는 주 스위치 턴온 시 보조 스위치를 함께 동작시켜 경부하시에도 강제적으로 영전압 스위칭이 가능하게 함으로써 전 부하범위에서 주 스위치 손실을 저감하였다. 그러나 보조 스위치에서의 손실이 크며 주 스위치의 턴온시 역방향 전류가 증가하는 문제점을 지닌다. 따라서 본 연구에서는 기존의 ZVT 컨버터에 단지 하나의 다이오드를 추가함으로써 보조 스위치의 전류 스트레스 및 주 스위치의 턴온시 역방향 전류를 감소시키게 되어 효율 향상을 기할 수 있었다. 본 논문에서는 MOSFET를 사용하여 640[W]급 시작품을 제작, 100[kHz]에서 실험하였다.

• 전기전자학회논문지
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• 제25권1호
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• pp.206-211
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• 2021

본 논문에서는 열전에너지 하베스팅을 위한 자가 리셋(self-reset) 기능을 갖는 영점 전류 스위칭(Zero-Current Switching) 회로를 제안한다. 본 논문에서 제안하는 영점 전류 스위칭 회로는 전압비교기 회로에 자가 리셋 기능을 추가하여 전압비교기의 동작전류를 최소화함으로써 에너지 하베스팅 회로의 전력 소비를 줄이고 에너지 변환 효율을 향상시킬 수 있게 한다. 회로 시뮬레이션으로 본 논문에서 제안하는 영전 전류 스위칭 회로의 동작을 검증하고 성능을 평가한 결과, 열전에너지 하베스팅 회로의 출력전압-입력전압 비가 5.5 일 때, 기존의 영점 전류 스위칭 회로를 이용한 하베스팅 회로와의 비교를 통해서 본 논문의 하베스팅 회로의 전력효율이 3.4% 개선되는 것으로 평가된다. 본 논문에서 제안하는 영점 전류 스위칭 회로는 열전에너지 하베스팅의 응용 중에서 특히 저전력과 고에너지 효율 특성이 중요한 웨어러블, 바이오 헬스 관련된 하베스팅 회로의 성능 개선에 기여할 수 있을 것으로 생각된다.