• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.390-395
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• 2004

The characteristics of the circular arc shaped multi-blade windmil are investigatedl. The prototypical windmill was tested in the laboratory at wind tunnel speeds of 5.5, 9.4m/s. and the model windmill was also tested in the laboratory, The power and torque coefficients were studied as functions of the blade section, the aspect ratio for blade diameter and windmill radius(M = 0.3, 0.5, 0.7), the number of blades and finally the tip-speed ratio. The analysis of the experimental results for the model windmill showed that there is the highest revolutions per minute(R.P.M) at the circular arc shaped multi-blade windmill having the blade number 10, aspect ratio(M = 0.7). and the results for the prototypical windmill showed that the power coefficient increased to a maximum value and then decreased again with an increase in the tip speed ratio, while the torque coefficient decreased directly with an increase in the tip speed ratio Finally, the experimental results were compared with the Savonius blade. the maximum power coefficient for the arc shaped blade was greater than for the Savonius blade and occured at a lower tip speed ratio.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.747-748
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• 2008

• Journal of Biomedical Engineering Research
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• v.22 no.2
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• pp.197-204
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• 2001

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.4
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• pp.145-151
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• 2005

Natural gas is one of clean fuels that can replace petroleum-based fuels, because it has low exhaust emission, comparatively high thermal efficiency and abundant deposits. In this addition, owing to high octane number and wide lean flammability limit, it has a strong point to increase the compression ratio. For this reason, the research is being actively executed to increase the generating power and thermal efficiency of the engine by raising the compression ratio through utilization of high octane number relevant to development of CNG engine. In this study, 0.63L single cylinder diesel engine has been used to alter easily compression ratio. Compression ratio has gotten under control by modifying the thickness of gasket between cylinder head and block without major structural modifications. As the result, as compression ratio has increased, generating power and fuel consumption ratio have been improved. As for emission concentration, as compression ratio has increased, THC concentration has been decreased while exhause concentration of NOx increased. In case compression ratio has excessively increased, brake output decrease and cycle variation have been increased. As the result acquired by analyzing brake output, fuel consumption ratio, cycle variation and exhaust, the engine driving condition has acquired $\varepsilon=13$ as the optimal compression ratio in this study.

• Journal of Power Electronics
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• v.15 no.6
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• pp.1468-1479
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• 2015

Renewable energy resources such as wind and photovoltaic power generation systems demand a high step-up DC-DC converters to convert the low voltage to commercial grid voltage. However, the high step-up converter using a transformer has limitations of high voltage stresses of switches and diodes when the transformer winding ratio increases. Accordingly, conventional studies have been applied to series-connect multioutput converters such as forward-flyback and switched-capacitor flyback to reduce the transformer winding ratio. This paper proposes new single-ended converter topologies of an isolation type and a non-isolation type to improve power efficiency, cost-effectiveness, and output ripple. The first proposal is an isolation-type charge-pump switched-capacitor flyback converter that includes an extreme-ratio isolation switched-capacitor cell with a chargepump circuit. It reduces the transformer winding number and the output ripple, and further improves power efficiency without any cost increase. The next proposal is a non-isolation charge-pump switched-capacitor-flyback tapped-inductor boost converter, which adds a charge-pump-connected flyback circuit to the conventional switched-capacitor boost converter to improve the power efficiency and to reduce the efficiency degradation from the input variation. In this paper, the operation principle of the proposed scheme is presented with the experimental results of the 100 W DC-DC converter for verification.

• Transactions of the Korean hydrogen and new energy society
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• v.26 no.4
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• pp.369-376
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• 2015

Recently KEPCO, KOGAS and other institutions are jointly conducting an R&D for the development and demonstration of the power generation system based on a natural gas/diesel engine on an island. As a preliminary study, co-combustion in the dual fuel engine, which is expected to produce a few mega-watts of electricity, was modeled and calculated using computational fluid dynamics (CFD). The applied key assumptions are 2-dimensional axisymmetric, transient and static volume chemical reaction. Based on the selected blending ratio, which is the key operating condition, natural gas is substituted instead of diesel fuel (basis of high heating value). Results showed that as the blending ratio increases, the reaction rate of the combustion increases and thus maximum temperature is reached more rapidly. For the optimal performance, various geometric or operational studies will further be conducted.

• Transactions on Electrical and Electronic Materials
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• v.18 no.1
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• pp.30-34
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• 2017

The building integrated photovoltaic system (BIPV) attracts attention with regard to the future of the photovoltaic (PV) industry. It is because one of the promising national and civilian projects in the country. Since land area is limited, there is considerable interest in BIPV systems with a variety of angles and shapes of PV panels. It is therefore expected to be one of the major fields for the PV industry in the future. Since the irradiation is different from each installation angle, the output can be predicted by the angles. This is critical for a PV system to be operated at maximum power and use an efficient design. The development characteristics of tilted angles based on data results obtained via long-term monitoring need to be analyzed. The ratio of the theoretically available and actual outputs is compared with the installation angles of each PV module to provide a suitable PV system for the user.

• Journal of Power Electronics
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• v.16 no.3
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• pp.872-882
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• 2016

A novel pseudo-continuous conduction mode (PCCM) voltage-fed single-stage power factor correction (PFC) full-bridge battery charger is proposed in this paper. By connecting a freewheeling transistor in parallel with an input inductor, the PFC cell can operate in the PCCM with a constant duty ratio. Thus, the dc/dc stage can be designed using this constant duty ratio and the restriction on the duty ratio of the PFC cell is eliminated. As a result, the input current distortion is less and the dc bus voltage becomes controllable over the wide output power range of the battery charger. Moreover, the operation principle of the dc/dc stage is designed to be similar to that of a conventional phase-shifted full-bridge converter. Therefore, it is easy to implement. In this paper, the operation of the new converter is explained, and the design considerations of the controller and key parameters are presented. Simulation and experimental results obtained from a 1 kW prototype are given to confirm the operation of the proposed converter.

• International Journal of Precision Engineering and Manufacturing
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• v.6 no.1
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• pp.5-14
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• 2005

Continuously variable transmission (CVT) mechanisms combine the functions of a K-H-V type differential gear unit and a V-belt type continuously variable unit (CVU). For the 24 different mechanisms, 12 of them are power circulation modes while the other 12 are power split modes. Some useful theoretical formulas related to speed ratio, power flow and efficiency were derived and analyzed. These mechanisms have many advantages: they decrease CVT size and weight, increase overall efficiency, extend speed ratio range, and generate geared neutral. Compound CVTs were developed by combining the power circulation mode and power split mode, which can offer backward motion, geared neutral, underdrive and overdrive.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.4
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• pp.84-91
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• 2003

The paper presents a power control algorithm for a full pitch-controlled wind power system. The design of a pitch controller, in general, is performed by linearizing the torque in the vicinity of a operating point assuming the tip speed ratio is constant. For power control, however, the tip speed ratio is no longer a constant. In this study, a reference pitch model is derived in terms of a wind speed, angular velocity, and pitch angle. The reference pitch model is used to design a controller without linearizing the non-linear torque model of the blade. The validity of the algorithm is demonstrated with the results produced through sets of simulation.