• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.213-213
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• 2010

In this thesis, we studied to increased to solar conversion efficiency of DSSC (dye-sensitized solar cell) using nanocrystalline $TiO_2$ semiconductor. We are preparation of $TiO_2$ photoelectrode, assembly the DSSC and put a focus in analyses electrochemical properties of DSSC and using Silica powder in $TiO_2$ photoelectrode for increase light scattering effect and improved conversion efficiency. It attempt to investigate the morphology of the photoelectrode and photovoltaic effects using field emission scanning electron microscopy (FE-SEM) and photovoltaic properties under illumination with AM 1.5 simulated sunlight. We got 146 % enhanced power conversion efficiency when the optimal content of quartz glass powder was 5 wt.% than that another content.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.413-414
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• 2014

This paper proposed an optimized design of a dual active bridge converter for a low-voltage charger. The dual active bridge converter among various bi-directional DC/DC converters is a high-efficiency isolated bi-directional converter. In the general design, when the battery voltage is high, the ZVS region is reduced. In contrast, when the battery voltage is low, the efficiency is low due to high conduction loss. In order to increase the ZVS region and the power conversion efficiency, depending on the battery voltage, variable switching frequency method is applied. At the same duty, the same power is obtained regardless of the battery voltage using the variable switching frequency method. The proposed method was applied to a 5kW prototype converter, and the experimental results were analyzed and verified.

• Journal of the Korean Ceramic Society
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• v.52 no.4
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• pp.229-233
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• 2015

Currently, the majority of commercial white LEDs are phosphor converted LEDs made of a blue-emitting chip and YAG yellow phosphor dispersed in organic silicone. However, silicone in high-power devices results in long-term performance problems such as reacting with water, color transition, and shrinkage by heat. Additionally, yellow phosphor is not applicable to warm white LEDs that require a low CCT and high CRI. To solve these problems, mixing of green phosphor, red phosphor and glass, which are stable in high temperatures, is common a production method for high-power warm white LEDs. In this study, we fabricated conversion lenses with LUAG green phosphor, SCASN red phosphor and low-softening point glass for high-power warm white LEDs. Conversion lenses can be well controlled through the phosphor content and heat treatment temperature. Therefore, when the green phosphor content was increased, the CRI and luminance efficiency gradually intensified. Moreover, using high heat treatment temperatures, the fabricated conversion lenses had a high CRI and low luminance efficiency. Thus, the fabricated conversion lenses with green and red phosphor below 90 wt% and 10 wt% with a sintering temperature of $500^{\circ}C$ had the best optical properties. The measured values for the CCT, CRI and luminance efficiency were 3200 K, 80, and 85 lm/w.

• Journal of Animal Environmental Science
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• v.18 no.2
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• pp.63-74
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• 2012

This experiment was carried out to investigate the effect of different stocking rate on growth, cast production and conversion efficiency of organic matter to tissues of earthworm. The carbon and nitrogen ratio (C/N) of tested Korean cow manure was 25.1, it was estimated an adequate ratio as feed for earthworms. The different stocking rates were 1:8(S-1), 1:16(S-2), 1:32(S-3) 1:64(S-4) 1:128(S-5) and 1:256 (S-6) as the ratios of earthworm fresh weight to biomass of Korean cow manure, respectively. A stocking rate of 1:32(S-3) was obtained a significantly highest values of increasing rate and conversion efficiency of organic matter to earthworm tissues. The mean values of increasin g rate of fresh weight and conversion efficiency of organic matter to earthworm tissues were 10.63 mg/day and 6.65% at the ratio of 1:32(S-3) with a rearing volume was $56.6cm^3$. A stocking rate of 1:8(S-1) was obtained a highest ratio of vermicasts, but showed a negative values of increasing rate and conversion efficiency of organic matter to earthworm tissues, it may due to severely food competition between individuals during the rearing periods. The pH, total nitrogen, available phosphorus, cation exchange capacity and exchangeable cations of vermicasts tended to increase with stocking rate. Especially, available phosphorus, cation exchange capacity and exchangeable cations of vermicasts tended to increase with rearing progressed. Vermicasts have the potential for improving plant growth when amended to container medium and soil according to increased availability of nutrients and improved physicochemical properties.

• Plant Journal
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• v.16 no.4
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• pp.26-32
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• 2020

The performance monitoring system in the power plant should have the capability to estimate power generation efficiency accurately. Several power generation efficiency models have been proposed for the combined heat and power (CHP) plant which produces both electricity and process steam(or heating energy, hereinafter expressed by process steam only). However, most of the models are not sufficiently accurate due to the wrong evaluation of the process steam value. The study suggests Electricity Conversion Efficiency (ECE) model with determination of the heat rate of process steam using operational data. The suggested method is applied to the design data and the resulted trajectory curve of power generation efficiency meets the data closely with R2 99.91%. This result confirms that ECE model with determination of the model coefficient using the operational data estimate the efficiency so accurately that can be used for performance monitoring of CHP plant.

• Proceedings of the KIEE Conference
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• 1998.07f
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• pp.1951-1953
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• 1998

In this study, we present the power conversion system of the passive transponder which is operated at 2.4GHz. First, The passive transponder which is the power conversion system is one of the passive transponder elements is presented. And then the power conversion system is analyzed and simulated.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.3 s.40
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• pp.19-26
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• 2006

In this paper, author proposes to a fuel cell generation system used to fire prevention installation at emergency. The proposed system is used with a power source of fire prevention installation in preparation for breaking of commercial power supply at emergency. A part of most power loss of the fuel cell generation system is power converter. And the major losses of power converter are switching losses of power semiconductor switches used to power conversion. This parer is designed with a high efficiency power converter of non isolated type in order to increase efficiency of fuel cell power system. The controlling switches used in power conversion system are operated with soft switching, which is applied to partial resonant method to reduce switching loss. The result is that the fuel cell power system gets to high efficiency. Some computer simulated results and experimental results are confirmed to the validity of the analytical results.

• Journal of the Korean Chemical Society
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• v.55 no.2
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• pp.279-282
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• 2011

Dye-sensitized solar cell (DSSC); an alternate energy source harvester has gained some attractive features such as high-energy conversion efficiency low production cost. Dye-sensitizer is a basic component of DSSC, which affecting the performance of the energy conversion efficiency. Current research has been focusing on development of high efficiency, metal-free dye-sensitizers, which would be more environmental friendly. We had successfully explored synthetic route to 6,6'-(1,2,5-oxadiazole-3,4-diyl)dipyridine-2,4-dicarboxylic acid (3A) which has been used as organic sensitizer. Investigation of light conversion efficiency (${\eta}$) of the compound uses standard measurement condition (one sun simulated irradiation, AM 1.5, 100 mW/$cm^2$) showed that it could reach 1.00% ($J_{SC}=2.63\;mAcm^{-2}$, $V_{OC}$=0.64 V and FF=0.59). Under the same conditions, the ruthenium complex (N719) gave the conversion efficiency as high as 4.02%($J_{SC}=10.50\;mAcm^{-2}$, $V_{OC}$=0.67V and FF=0.57).

• Journal of IKEEE
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• v.23 no.2
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• pp.538-542
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• 2019

Semiconductor oxides such as $TiO_2$ involved in light conversion efficiency are the main elements of dye-sensitized solar cells (DSSC) and are used to mix different semiconductor oxides to improve efficiency. In this research, characteristics of the dye-sensitive solar cell are studied using semiconductor oxide formed by mixing $TiO_2$ and $Nb_2O_5$. A solar cell is manufactured by adding $Nb_2O_5$ at different ratios in order to analyze electrical characteristics of a mixed semiconductor oxide on light conversion efficiency. With the addition of $Nb_2O_5$, the conductivity was further enhanced than the recombination phenomenon caused by contact with electrolytes, confirming the improve of short-circuit, open voltage, and conversion efficiency of solar cells.

• Journal of the Korean Ceramic Society
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• v.51 no.6
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• pp.533-538
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• 2014

Today, silicon and epoxy resin are used as materials of conversion lenses for white LEDs on the basis of their good bonding and transparency in LED packages. But these materials give rise to long-term performance problems such as reaction with water, yellowing transition, and shrinkage by heat. These problems are major factors underlying performance deterioration of LEDs. In this study, in order to address these problems, we fabricated a conversion lenses using glass, which has good chemical durability and is stable to heat. The fabricated conversion lenses were applied to a remote phosphor type. In this experiment, the conversion lens for white LED was coated on a glass substrate by a screen printing method using paste. The thickness of the coated conversion lens was controlled during 2 or 3 iterations of coating. The conversion lens fabricated under high heat treatment temperature and with a thin coating showed higher luminance efficiency and CCT closer to white light than fabricated lenses under low heat treatment temperature or a thick coating. The conversion lens with $32{\mu}m$ coating thickness showed the best optical properties: the measured values of the CCT, CRI, and luminance efficiency were 4468 K, 68, and 142.22 lm/w in 20 wt% glass frit, 80 wt% phosphor with sintering at $800^{\circ}C$.