• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.9
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• pp.1763-1770
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• 2016

This paper proposed hybrid converter to operate over a wide output load power. The switched-capacitor converter has a high efficiency at low load power and a low efficiency at high load power. On the contrary, the buck converter has a high efficiency at high load power and a low efficiency at low load power. The proposed hybrid converter has combination of the switched-capacitor converter and the buck converter. The switched-capacitor operates at low load power and buck converter operates at high load power, so that the hybrid converter is improved power efficiency at wide output load power. The hybrid converter was implemented with a $0.18{\mu}m$ CMOS process. The hybrid converter has a range of the load power between $50{\mu}W$and 100mW. The maximum power efficiencies are 93% and 77% at the buck converter and the switched-capacitor converter, respectively.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.7-10
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• 2001

This paper provides a solution for the problem of efficiency decrease caused by load variation. A novel control scheme of tracking the PT's operation frequency for the maximum efficiency is proposed. As a result, a high efficiency over $80\%$ has been achieved even under the output-current decrease down to $10\%$ of the full load current.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.31 no.7
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• pp.25-30
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• 1982

This paper considered the energy saving problem of D.C. motor in arbitrary load condition. We can improve efficiency by maintaining the proper ratio of armature current/field current. First, the condition of maximizing the efficiency was obtained, and then the real time control was implemented by using microprocessors. As a result, the efficiency was improved in spite of constant output. For example, the efficiency at 1/5 load was improved from 56.7% to 80%.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.8
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• pp.945-952
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• 2015

Power amplification device which is matched to $50{\Omega}$ in order to achieve a high efficiency of a power amplifier using a GaN power amplification device, since there is a limit of application frequency bands, output power, efficiency characteristics selection, in this study based on the measurement data through the source/load-pull test, high output power and to extract quantitative input and output impedance that matches the design objectives of high output power, high efficiency, an implementation of the high efficiency power amplifier. Implemented power amplifier is shows 25watt(44dBm), PAE of 66-76% characteristics in the frequency band of 2.7-3.1 GHz.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.290-297
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• 2002

This paper presents analysis results for the effect of power control strategies on the part load performance of gas turbine based power generation systems utilizing exhaust heat of the gas turbine such as cumbined cycle power plants and regenerative gas turbines. For the combined cycle, part load efficiency variations were compared among different single shaft gas turbines representing various technology levels. Power control strategies considered were fuel only control and IGV control. It has been observed that gas turbines with higher design performances exhibit superior part load performances. Improvement of part load efficiency by adopting air flow modulation was analyzed and it is concluded that since the average combined cycle performance is affected by the range of IGV control as well as its temperature control principle, a control strategy appropriate for the load characteristics of the individual plant should be adopted. For the regenerative gas turbine, it is likewise concluded that maintaining exhaust temperature as high as possible by air flow rate modulation is required to increase part load efficiency.

• The KSFM Journal of Fluid Machinery
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• v.6 no.3 s.20
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• pp.28-35
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• 2003

This paper presents analysis results for the effect of power control strategies on the part load performance of gas turbine based power generation systems utilizing exhaust heat of the gas turbine such as combined cycle power plants and regenerative gas turbines. For the combined cycle, part load efficiency variations were compared among different single shaft gas turbines representing various technology levels. Power control strategies considered were fuel only control and IGV control. It has been observed that gas turbines with higher design performances exhibit superior part load performances. Improvement of part load efficiency of the combined cycle by adopting air flow modulation was analyzed and it was concluded that since the average combined cycle performance is affected by the range of IGV control as well as its temperature control principle, a control strategy appropriate for the load characteristics of the individual plant should be adopted. For the regenerative gas turbine, it is likewise concluded that maintaining exhaust temperature as high as possible by air flow rate modulation is required to increase part load efficiency.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.4
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• pp.493-500
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• 2015

A flyback converter operates with either pulse width modulation (PWM) or pulse frequency modulation (PFM) control scheme depending on the load current. At light load condition, PFM control is employed to reduce the switching frequency and thereby minimize the switching power loss. For heavier load, PWM control is used to regulate the output voltage of the flyback converter. The flyback controller has been implemented in a $0.35{\mu}m$ BCDMOS process and applied to a 40-W flyback converter. The light-load power efficiency of the flyback converter is improved up to 5.7-% comparing with the one operating with a fixed switching frequency.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.279-282
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• 2005

Recently, due to the launching of digital broadcasting service, a demand of PDP TV with large screen size is sharply rising. PDP power module is mainly divided into power factor correction (PFC) stage and sustaining power stage. Especially, sustaining power module has pulsating load characteristics. So, the hard switching at light load condition causes low efficiency and thermal problem. Therefore, a new power conversion circuit for sustaining power module of 60' PDP is proposed whose ZVS is obtained by additional ZVS tank. This paper presents properties of the proposed converter through mode analysis, numerical analysis. And a 900w prototype for sustaining power module of 60' PDP is produced to verify the analytic results. As an experimental results, ZVS is achieved from full load to 10% load variation and more than 92% of high efficiency is obtained at 10% load condition.

• Transactions of the Korean hydrogen and new energy society
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• v.13 no.4
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• pp.304-312
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• 2002

In this study, the performance of the $5Nm^3/hr$ compact type steam reformer which was developed for application of fuel cell or hydrogen station was evaluated in terms of gas process efficiency. For these purposes, reforming efficiency and total efficiency with system load change were analyzed. The reforming efficiency was calculated from the total molar flow of hydrogen output over total fuel flow input to the reformer and the burner on the higher heating value(HHV). In the case of the total efficiency, recovered heat at the heat recovery exchanger was considered. From the results, it was known that system performance was stable, because methane conversion showed the a slight decline which is about 2% though increasing system load to full. Reforming efficiency was increased from 20% to 58%, respectively as increasing system load from 10% to 90%. It was found that total efficiency was higher then reforming efficiency because of terms of heat recovered. As a results, it was known that total efficiency was increased form 75% to 83% at the 10% and 90% system load, respectively. From these results, it is concluded that compact steam reformer which is composed of stacking plate-type reactors is suitable to on-site hydrogen generator or to fuel cell application because of quick start within 1 hr and good performance.

• Fire Science and Engineering
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• v.25 no.1
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• pp.1-6
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• 2011

An evacuation simulation was carried out to confirm evacuation efficiency for stair width and problems in calculation of occupant load for high-rise buildings. The evacuation time and number of evacuated persons from a 39 story condominium-mercantile building were calculated by using Simulex for stair widths of 1.2 m, 1.5 m, and 1.8 m. The total occupant load based on the Korean code was higher than the number of actual residents by 2.3 times, and that based on the NFPA 101 Life Safety Code by 2.6 times, respectively. For the occupant load based on the Korean code, smaller stair width resulted in lower evacuation efficiencies due to bottlenecks in egress. For the actual residents and NFPA code-based occupant load, a high evacuation efficiency and negligible effects of the stair width on evacuation efficiency were confirmed. It was shown that there was a bottleneck even at the stair width of 1.8 m for the Korean code-based occupants, while the stair width of 1.2 m provided safe egress to the actual residents or NFPA code-based occupants. This recommended further studies on possibility of lowering the level of the Korean code in calculation of the occupant load.