• Korean Journal of Materials Research
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• v.18 no.11
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• pp.571-576
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• 2008

The simulation program for solar cells, PC1D, was briefly reviewed and the device modeling of a multicrystalline Si solar cell using the program was carried out to understand the internal operating principles. The effects of design parameters on the light absorption and the quantum efficiency were investigated and strategies to reduce carrier recombination, such as back surface field and surface passivation, were also characterized with the numerical simulation. In every step of the process, efficiency improvements for the key performance characteristics of the model device were determined and compared with the properties of the solar cell, whose efficiency (20.3%) has been confirmed as the highest in multicrystalline Si devices. In this simulation work, it was found that the conversion efficiency of the prototype model (13.6%) can be increased up to 20.7% after the optimization of design parameters.

• Journal of Korea Foundry Society
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• v.29 no.1
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• pp.33-37
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• 2009

Cartesian grid system has mainly been used in the casting simulation even though it does not nicely represent sloped and curved surfaces. These distorted boundaries cause several problems. A special treatment is necessary to clear these problems. In this paper, we propose a new method that can consider the cutting cells which are cut by casting and mold based on the partial cell treatment (PCT). This method provides a better representation of geometry surface and will be used in the computation of velocities that are defined on the cell boundaries in the Cartesian grid system. Various test examples for several casting process were computed and validated. The analysis results of more accurate fluid flow pattern and less momentum loss owing to the stepped boundaries in the Cartesian grid system were confirmed. By using the cut cell method, performance of computation gets better because of reducing the whole number of meshes.

• Molecules and Cells
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• v.37 no.6
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• pp.497-502
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• 2014

Microfluidics can provide unique experimental tools to visualize the development of neural structures within a microscale device, which is followed by guidance of neurite growth in the axonal isolation compartment. We utilized microfluidics technology to monitor the differentiation and migration of neural cells derived from human embryonic stem cells (hESCs). We co-cultured hESCs with PA6 stromal cells, and isolated neural rosette-like structures, which subsequently formed neurospheres in suspension culture. Tuj1-positive neural cells, but not nestin-positive neural precursor cells (NPCs), were able to enter the microfluidics grooves (microchannels), suggesting that neural cell-migratory capacity was dependent upon neuronal differentiation stage. We also showed that bundles of axons formed and extended into the microchannels. Taken together, these results demonstrated that microfluidics technology can provide useful tools to study neurite outgrowth and axon guidance of neural cells, which are derived from human embryonic stem cells.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.48 no.8
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• pp.18-24
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• 2011

A new problem happens with the evolution of TSV based 3D IC design. The bonding process takes place which follows with the testing of design for proper connectivity in the absence of TSV redundancy. In order to achieve good yield, the design should be tested with redundancy TSV. This paper presents a wrapper cell design for redundancy TSV interconnect test. The design for test technique, in terms of hardware and software perspectives is described. The wrapper cell with hardware design can use original test patterns. However, software design has less area overhead.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.4
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• pp.247-255
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• 2018

This paper proposes a transformer design of a direct cell-to-cell active cell balancing circuit with a multi-winding transformer for battery management system (BMS) applications. The coupling coefficient of the multi-winding transformer and the output capacitance of MOSFETs significantly affect the balancing current transfer efficiency of the cell balancing operation. During the operation, the multi-winding transformer stores the energy charged in a specific source cell and subsequently transfers this energy to the target cell. However, the leakage inductance of the multi-winding transformer and the output capacitance of the MOSFET induce an abnormal energy transfer to the non-target cells, thereby degrading the transfer efficiency of the balancing current in each cell balancing operation. The impacts of the balancing current transfer efficiency deterioration are analyzed and a transformer design methodology that considers the coupling coefficient is proposed to enhance the transfer efficiency of the balancing current. The efficiency improvements resulting from the selection of an appropriate coupling coefficient are verified by conducting a simulation and experiment with a 1 W prototype cell balancing circuit.

• International Journal of Automotive Technology
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• v.8 no.1
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• pp.119-126
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• 2007

Because of the low temperature operation, proton exchange membrane (PEM) fuel cell has a water phase transition. Therefore, water management is an important operation issue in a PEM fuel cell because the liquid water in the fuel cell causes electrode flooding that can lower the cell performance under high current density conditions. In this study, in order to understand the reactant distributions in the cathode channels of the PEM fuel cell, an experimental technique that can measure the species concentrations of reactant gases by using gas chromatograph (GC) is applied for an operating PEM fuel cell. The oxygen distribution along the cathode flow channels of PEM fuel cell is mainly investigated with various operating conditions. Also, the relations between cathode flooding and oxygen concentrations and oxygen consumption pattern along the cathode channel configurations of the unit cell adopted for this study are discussed using GC measurement and visualization experiment of cathode flooding. It is found that the amount of oxygen consumption is very sensitive to various operating conditions of the fuel cell and was much affected by the flooding occurrence in cathode channels.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.3
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• pp.226-231
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• 2022

Power converter are usually equipped for fuel cell power generation system to connect alternating current (AC) electric power grid. When converting direct current (DC) of fuel cell power source into AC, the power converter has a frequency ripple, which affects the fuel cell and the grid. Therefore, an equivalent circuit having dynamic characteristics of fuel cell power, for example, impedance, is useful for designing an inverter circuit. In this study, the current, voltage and impedance characteristics were calculated through fuel cell modeling and validated by comparing them with experiments. The equivalent circuit element values according to the current density were formulated into equations so that it could be applied to the circuit design. It is expected that the process of the equivalent circuit modeling will be applied to the actual inverter circuit design and simulated fuel cell power sources.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.6
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• pp.1003-1011
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• 2008

In this paper, optimal design of interleaved boost converters is studied in order to design low ripple, size, loss and high performance converters for fuel cell applications. Also, the process of optimal design of interleaved boost converter has been performed. Input current ripple, output voltage ripple, losses and capacity of electrical components are theoretically analyzed and informative simulation and experimental results are provided.

• Journal of Integrative Natural Science
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• v.7 no.3
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• pp.208-213
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• 2014

National-wide and/or large scale sample surveys generally use complex sample design. Traditional Pearson chi-square test is not appropriate for the categorical complex sample data. Rao-Scott suggested an adjustment method for Pearson chi-square test, which uses the average of eigenvalues of design matrix of cell probabilities. This study is to compare the efficiency of Rao-Scott first order adjusted test to Wald test for homogeneity between two populations using 2009 Gyeongnam regional education offices's customer satisfaction survey (2009 GREOCSS) data. The 2009 GREOCSS data were collected based on stratified three-stage cluster sampling with probability proportional to size. The empirical results show that the Rao-Scott adjusted test statistic using only the variances of cell probabilities is very close to the Wald test statistic, which uses the covariance matrix of cell probabilities, under the 2009 GREOCSS data based. However it is necessary to be cautious to use the Rao-Scott first order adjusted test statistic in the place of Wald test because its efficiency is decreasing as the relative variance of eigenvalues of the design matrix of cell probabilities is increasing, specially more when the number of degrees of freedom is small.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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• pp.1361-1369
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• 2003

Design performance of hybrid power generation systems, comprised of a gas turbine and an atmospheric pressure molten carbonate fuel cell, has been analyzed. Two different configurations were analyzed and performances were compared. A reference calculation was performed for the design condition of a system under development and simulated results agreed well with the published data. Performances were analyzed in terms of main design parameters including turbine inlet temperature, operating temperature of the fuel cell and pressure ratio. Also examined were the effects of fuel utilization factor and heat exchanger effectiveness. It was found that the relationship between the turbine inlet temperature and the fuel cell temperature should be critically examined to evaluate achievable design performance. Considering current state of the art technologies, a system with the combustor located before the turbine could achieve higher efficiency and specific power than the other system with the combustor located after the turbine.