• 조명전기설비학회논문지
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• 제22권5호
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• pp.13-20
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• 2008

과거에는 순간전압강하(Sag)나 고조파(Harmonics)와 같은 순간전력품질 문제가 부하에 큰 영향을 미치지 않았으나, 최근 컴퓨터와 같은 마이크로 프로세서를 이용하는 민감부하의 사용 증가로 인하여 전력품질에 대한 관심이 고조되고 있다. 이에 따라 현재까지 영구정전(Sustained Interruption)에 초점을 맞추고 일부 순간정전(Momentary Interruption)을 포함하여 진행되어 온 배전계통 신뢰도 연구 분야는 새로운 전환점을 맞이하고 있다. 즉, 전력품질문제로 인하여 많은 민감기기들이 트립(Trip)되어 신뢰도 비용이 발생하기 때문에, 전력품질을 고려하지 않은 신뢰도 비용평가는 그 정확도가 떨어질 수밖에 없는 실정에 있다. 본 논문에서는 배전계통 사고 시 이 사고를 제거하기 위해 사용된 리클로져에 의해 발생하는 순간전압강하를 고려하였다. 기존의 영구정전에 의한 신뢰도 비용과 순간전압강하에 의해 트립되는 기기들의 신뢰도 비용을 포함하는 개선된 배전계통 신뢰도 비용 평가 기법을 제안하였다.

• 에너지공학
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• 제19권2호
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• pp.103-115
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• 2010

현재 전 세계적으로 신재생에너지의 개발과 이용에 관한 연구가 활발히 진행되고 있다. 조력에너지는 다른 재생에너지의 비해 안정적인 공급이 가능한 고급 자원이다. 본 논문에서는 조력에너지 대한 세계적인 연구 및 개발 동향을 고찰하였고 시화호 조력발전소와 울돌목 조류발전소의 경제성을 분석하였다. 댐 방식 조력발전은 경제성과 기술적 신뢰성이 있으나 상당한 환경적 논쟁이 있다. 반면, 조류식 조력발전은 완전한 상용화를 이루지 못하고 있으나 환경적 폐해가 거의 없는 것으로 평가되어 댐 방식 보다 더 많은 연구가 진행되고 있다. 시화호 조력발전인 경우 발전단가는 약 67.3원/kWh, 여기에 시화호의 조성비용을 추가로 고려할 경우 254원/kWh로 계산되었다. 반면 울돌목 조류발전의 발전단가는 약 400원/kWh로 이는 조류발전 기술이 성장 단계라 장비와 건설비용이 비싸고, 또한 아직 규모의 경제성이 적용되지 못한 결과라 하겠다.

• 전력전자학회논문지
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• 제22권4호
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• pp.277-284
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• 2017

For passive power factor correction, the valley fill circuit approach is attractive for low power applications because of low cost, high efficiency, and simple circuit design. However, to vouch for the product quality, two dc-link capacitors in the valley fill circuit should be selected to withstand the peak rectified ac input voltage. The common mode (CM) and differential mode (DM) choke should be used to suppress the electromagnetic interference (EMI) noise, thereby resulting in large size volume product. This paper presents the practical design and implementation of a valley fill flyback converter with reduced dc link capacitors and EMI magnetic volumes. By using the proposed over voltage protection circuit, dc-link capacitors in the valley fill circuit can be selected to withstand half the peak rectified ac input voltage, and the proposed CM/DM choke can be successfully adopted. The proposed circuit effectiveness is shown by simulation and experimentally verified by a 78W prototype.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.109-110
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• 2007

Most transmission lines pass through mountainous terrain and deep valleys, to avoid populated areas. Accordingly, the impact of climate changes, environmental conditions and system expansion have caused an increase in transmission line system fault rates. KEPCO has developed and applied phase-spacers to reduce contact faults between phases. Contact between phases represented 9% of total line faults before the devices were installed. Phase-spacers have reduced faults by up to 3.4% since the phase-spacers were installed in 2005. Also, recently developed devices provide additional economic benefits as they cost about a third of the price as similar devices introduced in foreign countries. Phase-spacers are an effective way to prevent phase contact accidents by maintaining physical space between phases. These spacers will be implemented in areas where contacts are likely to occur. They are expected to reduce accident rates and improve power quality.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권5호
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• pp.1973-1991
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• 2018

Multimedia applications over wireless networks have been evolving to augmented reality or virtual reality services. However, a rich data size compared to conventional multimedia services causes bandwidth bottlenecks over wireless networks, which is one of the main reasons why those applications are not used widely. To overcome this limitation, bandwidth aggregation techniques, which exploit a multi-path transmission, have been considered to maximize link utilization. Currently, most of the conventional researches have been focusing on the user end problems to improve the quality of service (QoS) through optimal load distribution. In this paper, we address the joint pricing and load distribution problem for multi-homing in heterogeneous wireless access networks (ANs), considering the interests of both the users and the service providers. Specifically, we consider profit from resource allocation and cost of power consumption expenditure for operation as an utility of each service provider. Here, users decide how much to request the resource and how to split the resource over heterogeneous wireless ANs to minimize their cost while supporting the required QoS. Then, service providers compete with each other by setting the price to maximize their utilities over user reactions. We study the behaviors of users and service providers by analyzing their hierarchical decision-making process as a multileader-, multifollower Stackelberg game. We show that both the user and service provider strategies are closed form solutions. Finally, we discuss how the proposed scheme is well converged to equilibrium points.

• Journal of Power Electronics
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• 제18권6호
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• pp.1729-1750
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• 2018

Voltage source inverters (VSIs) are widely used to drive induction motors in industry applications. The quality of output waveforms depends on the switching sequences used in pulse width modulation (PWM). In this work, all existing optimal space vector pulse width modulation (SVPWM) switching strategies are studied. The performance of existing SVPWM switching strategies is optimized to realize a tradeoff between quality of output waveforms and switching losses. This study generalizes the existing optimal switching sequences for total harmonic distortions (THDs) and switching losses for different modulation indexes and reference angles with a parameter called quality factor. This factor provides a common platform in which the THDs and switching losses of different SVPWM techniques can be compared. The optimal spatial distribution of each sequence is derived on the basis of the quality factor to minimize harmonic current distortions and switching losses in a sector; the result is the minimum ripple loss SVPWM (MRSLPWM). By employing the sequences from optimized switching maps, the proposed method can simultaneously reduce THDs and switching losses. Two hybrid SVPWM techniques are proposed to reduce line current distortions and switching losses in motor drives. The proposed hybrid SVPWM strategies are MRSLPWM 30 and MRSLPWM 90. With a low-cost PIC microcontroller (PIC18F452), the proposed hybrid SVPWM techniques and the quality of output waveforms are experimentally validated on a 2 kVA VSI based on a three-phase two-level insulated gate bipolar transistor.

• 한국근적외분광분석학회:학술대회논문집
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• 한국근적외분광분석학회 2001년도 NIR-2001
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• pp.1618-1618
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• 2001

Predicting quality traits using near infrared (NIR) spectroscopy on whole grain samples has gained wide acceptance as a non-destructive, rapid and cost effective technique. Barley breeding programs throughout southern Australia currently use this technology as a tool for selecting malting quality lines. For the past 3 years whole grain barley calibrations have been developed at VIDA to predict malting quality traits in the early generation selections of the breeding program. More recently calibrations for whole grain malt have been developed and introduced to aid in selecting malted samples at the mid-generation stage for more complex malting quality traits. Using the same population set, barley and malt calibrations were developed to predict hot water extracts (EBC and IoB), diastatic power, free $\alpha$-amino nitrogen, soluble protein, wort $\beta$-glucan and $\beta$-glucanase. The correlation coefficients between NIR predicted values and laboratory methods for malt were all highly significant ($R^2$ > 0.84), whereas the correlation coefficients for the barley calibrations were lower ($R^2$ > 0.57) but still significant. The magnitude of the error in predicting hot water extract, diastatic power and wort $\beta$-glucan using whole grain malt was reduced by 50% when compared with predicting the same trait using whole grain barley. This can be explained by the complex nature of attempting to develop calibrations on whole grain barley utilizing malt data. During malting, the composition of barley is modified by the action of enzymes throughout the steeping and germination stages and by heating during the kilning stage. Predicting malting quality on whole grain malt is a more reliable alternative to predicting whole grain barley, although there is the added expense of micro-malting the samples. The ability to apply barley and malt calibrations to different generations is an advantage to a barley breeding program that requires thousands of samples to be assessed each year.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 C
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• pp.1245-1247
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• 1999

This paper describes the optimal reconfiguration of distribution network. The optimal routing of distribution network should provide electricity to customers with quality, and this paper shows that optimal routing of distribution network can be obtained by Neural-Tabu algorithm while keeping constraints such as line power capacity, voltage drop and reliability indices. The Neural-Tabu algorithm is a Tabu algorithm combined with Neural network to find neighborhood solutions. This paper shows that not only the loss cost but also the reliability cost should be considered in distribution network reconfiguration to achieve the optimal routing.

• 전기학회논문지
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• 제64권1호
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• pp.29-34
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• 2015

This paper presents a method to select optimal device for mitigating voltage sags. The method is based on economic evaluation and voltage sag assessment involving sag duration as well as magnitude. The economic evaluation is performed by using the operation cost and economic benefit of the mitigation devices. The optimal device can be determined from the values of NPV (net present value) which is widely accepted in cost-benefit analysis. The proposed method can help sensitive customers to select optimal mitigation device. In this paper, the case study considering two sensitive customers was performed by using the proposed method.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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• pp.13-13
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• 2010

The solar energy conversion will take 10 % global energy need by 2033. A thin film type solar cell has been considered as one of the promising candidates for a large area applicable solar cell fabrication at a low cost. The metal-assisted growth of microcrystalline Si (mc-Si) films has been reported for a quality Si film synthesis at a low temperature. It discusses the spontaneous growth of a Si film above a metal-layer for a thin film solar cell. Quite recently, a substantial demand of nanomaterials has been addressed for cost-effective solar cells. The nanostructure provides a large photoactive surface at a fixed volume, which is an advantage in the effective use of solar power. But the promising of nanostructure active solar cell has not been much fulfilled due mainly to the difficulty in architecture of nanostructures. We present here the Si nanowire (SiNW)-embedded Schottky solar cell. Multiple SiNWs were connected to two different metals to form a Schottky or an ohmic contact according to the metal work function values. It discusses the scheme of rectifying contact between metals and SiNWs and the SiNW-embedded Schottky solar cell performances.