The Experts below are selected from a list of 171708 Experts worldwide ranked by ideXlab platform
Kyoungdoug Min - One of the best experts on this subject based on the ideXlab platform.
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analysis of Transient Response of a unit proton exchange membrane fuel cell with a degraded gas diffusion layer
2011Co-Authors: Junhyun Cho, Kyoungdoug Min, Jaeman Park, Hansang Kim, Eunsook Lee, Jyyoung JyoungAbstract:The Transient Response characteristics and durability problems of proton-exchange membrane fuel cells are important issues for the application of PEM fuel cells to automotive systems. The gas diffusion layer is the key component of the fuel cell because it directly influences the mass transport mechanism. In this study, the effects of GDL degradation on the Transient Response of the PEM fuel cell are systematically studied using Transient Response analysis under different stoichiometric ratios and humidity conditions. With GDLs aged by the accelerated stress test, the effects of hydrophobicity and structural changes due to carbon loss in the GDL on the Transient Response of PEM fuel cells are determined. The cell voltage is measured according to the sudden current density change. The degraded GDLs that had uneven hydrophobicity distributions cause local water flooding inside the GDL and induce lower and unstable voltage Responses after load changes.
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Transient Response of a unit proton exchange membrane fuel cell under various operating conditions
2008Co-Authors: Junhyun Cho, Hansang Kim, Kyoungdoug MinAbstract:Abstract The Transient Response of proton-exchange membrane fuel cells (PEMFCs) is an important criterion in their application to automotive systems. Nevertheless, few papers have attempted to study experimentally this dynamic behaviour and its causes. Using a large-effective-area (330 cm 2 ) unit PEMFC and a transparent unit PEMFC (25 cm 2 ), systematic Transient Response and cathode flooding during load changes are investigated. The cell voltage is acquired according to the current density change under a variety of stoichiometry, temperature and humidity conditions, as well as different flooding intensities. In the case of the transparent fuel cell, the cathode gas channel images are obtained simultaneously with a CCD imaging system. The different levels of undershoot occur at the moment of load change under different cathode stoichiometry, both cathode and anode side humidity and flooding intensity conditions. It is shown that undershoot behaviour consists of two stages with different time delays: one is of the order of 1 s and the other is of the order of 10 s. It takes about 1 s for the product water to come up on to the flow channel surface so that oxygen supply is temporarily blocked, which causes voltage loss in that “undershoot”. The correlation of dynamic behaviour with stoichiometry and cathode flooding is analyzed from the results of these experiments.
Junhyun Cho - One of the best experts on this subject based on the ideXlab platform.
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analysis of Transient Response of a unit proton exchange membrane fuel cell with a degraded gas diffusion layer
2011Co-Authors: Junhyun Cho, Kyoungdoug Min, Jaeman Park, Hansang Kim, Eunsook Lee, Jyyoung JyoungAbstract:The Transient Response characteristics and durability problems of proton-exchange membrane fuel cells are important issues for the application of PEM fuel cells to automotive systems. The gas diffusion layer is the key component of the fuel cell because it directly influences the mass transport mechanism. In this study, the effects of GDL degradation on the Transient Response of the PEM fuel cell are systematically studied using Transient Response analysis under different stoichiometric ratios and humidity conditions. With GDLs aged by the accelerated stress test, the effects of hydrophobicity and structural changes due to carbon loss in the GDL on the Transient Response of PEM fuel cells are determined. The cell voltage is measured according to the sudden current density change. The degraded GDLs that had uneven hydrophobicity distributions cause local water flooding inside the GDL and induce lower and unstable voltage Responses after load changes.
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Transient Response of a unit proton exchange membrane fuel cell under various operating conditions
2008Co-Authors: Junhyun Cho, Hansang Kim, Kyoungdoug MinAbstract:Abstract The Transient Response of proton-exchange membrane fuel cells (PEMFCs) is an important criterion in their application to automotive systems. Nevertheless, few papers have attempted to study experimentally this dynamic behaviour and its causes. Using a large-effective-area (330 cm 2 ) unit PEMFC and a transparent unit PEMFC (25 cm 2 ), systematic Transient Response and cathode flooding during load changes are investigated. The cell voltage is acquired according to the current density change under a variety of stoichiometry, temperature and humidity conditions, as well as different flooding intensities. In the case of the transparent fuel cell, the cathode gas channel images are obtained simultaneously with a CCD imaging system. The different levels of undershoot occur at the moment of load change under different cathode stoichiometry, both cathode and anode side humidity and flooding intensity conditions. It is shown that undershoot behaviour consists of two stages with different time delays: one is of the order of 1 s and the other is of the order of 10 s. It takes about 1 s for the product water to come up on to the flow channel surface so that oxygen supply is temporarily blocked, which causes voltage loss in that “undershoot”. The correlation of dynamic behaviour with stoichiometry and cathode flooding is analyzed from the results of these experiments.
F C Lee - One of the best experts on this subject based on the ideXlab platform.
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critical bandwidth for the load Transient Response of voltage regulator modules
2004Co-Authors: Kaiwei Yao, Yuancheng Ren, F C LeeAbstract:This paper investigates the relationship between the control bandwidth and the load Transient Response in voltage regulator modules (VRMs), which are designed with multiphase interleaving synchronous buck converters. Both voltage- and current-mode controls are discussed. A critical bandwidth value is discovered, beyond which pushing the bandwidth can no longer reduce the output voltage spike during the load Transient Response. Also, the critical bandwidths are different according to different kinds of output capacitors. The critical bandwidth concept highlights the trend of high-frequency VRM design that uses ceramic capacitors to achieve smaller size and faster load Transient Response. Simulation and experimental results prove the theoretical analysis.
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design considerations for vrm Transient Response based on the output impedance
2003Co-Authors: Kaiwei Yao, Yu Meng, F C LeeAbstract:This paper discusses the Transient Response of voltage regulator modules (VRMs) based on the small-signal models. The concept of constant resistive output impedance design for the VRM is proposed, and its limitations in applications are analyzed. The impacts of the output filter and the feedback control bandwidth show that there is an optimal design that allows the VRM to achieve fast Transient Response, small size and good efficiency. Simulations and experimental results prove the theoretical analysis.
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applying transformer concept to nonisolated voltage regulators significantly improves the efficiency and Transient Response
2003Co-Authors: J Wei, K Yao, F C LeeAbstract:A voltage regulator (VR) is a DC-DC converter dedicated to powering the microprocessors in today's computers. The multiphase buck converter, as the current solution, faces great challenges for future use in VRs. This paper applies the transformer concept to generate several families of new converters, therefore providing opportunities to improve the efficiency while maintaining good Transient Response. Topology derivation, analysis and experimental results are presented. Test results verify the theoretical prediction.
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optimal design of the active droop control method for the Transient Response
2003Co-Authors: Kaiwei Yao, Kisun Lee, F C LeeAbstract:Use of the active droop control method is a popular way to achieve adaptive voltage position (AVP) for the voltage regulator (VR). This paper discusses the small-signal model of the active droop control method, which is shown to be a two-loop feedback control system. The compensator design impacts both the current and voltage loops, making the design complicated. An optimal design method is proposed in order to achieve equal crossover frequencies for the two loops so that constant output impedance is realized in the VR. Simulation and experimental results prove the good VR Transient Response and high efficiency.
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design considerations for vrm Transient Response based on the output impedance
2002Co-Authors: Kaiwei Yao, Yu Meng, F C LeeAbstract:This paper discusses the Transient Response of voltage regulator modules (VRMs) based on small-signal models. The concept of constant resistive output impedance design for the VRM is proposed, and its limitation in application is analyzed. The impact of the output filter and the feedback control bandwidth shows that there is an optimum design for the VRM to achieve fast Transient Response, small size and good efficiency. Simulations and experimental results prove the theoretical analysis.
Hansang Kim - One of the best experts on this subject based on the ideXlab platform.
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analysis of Transient Response of a unit proton exchange membrane fuel cell with a degraded gas diffusion layer
2011Co-Authors: Junhyun Cho, Kyoungdoug Min, Jaeman Park, Hansang Kim, Eunsook Lee, Jyyoung JyoungAbstract:The Transient Response characteristics and durability problems of proton-exchange membrane fuel cells are important issues for the application of PEM fuel cells to automotive systems. The gas diffusion layer is the key component of the fuel cell because it directly influences the mass transport mechanism. In this study, the effects of GDL degradation on the Transient Response of the PEM fuel cell are systematically studied using Transient Response analysis under different stoichiometric ratios and humidity conditions. With GDLs aged by the accelerated stress test, the effects of hydrophobicity and structural changes due to carbon loss in the GDL on the Transient Response of PEM fuel cells are determined. The cell voltage is measured according to the sudden current density change. The degraded GDLs that had uneven hydrophobicity distributions cause local water flooding inside the GDL and induce lower and unstable voltage Responses after load changes.
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Transient Response of a unit proton exchange membrane fuel cell under various operating conditions
2008Co-Authors: Junhyun Cho, Hansang Kim, Kyoungdoug MinAbstract:Abstract The Transient Response of proton-exchange membrane fuel cells (PEMFCs) is an important criterion in their application to automotive systems. Nevertheless, few papers have attempted to study experimentally this dynamic behaviour and its causes. Using a large-effective-area (330 cm 2 ) unit PEMFC and a transparent unit PEMFC (25 cm 2 ), systematic Transient Response and cathode flooding during load changes are investigated. The cell voltage is acquired according to the current density change under a variety of stoichiometry, temperature and humidity conditions, as well as different flooding intensities. In the case of the transparent fuel cell, the cathode gas channel images are obtained simultaneously with a CCD imaging system. The different levels of undershoot occur at the moment of load change under different cathode stoichiometry, both cathode and anode side humidity and flooding intensity conditions. It is shown that undershoot behaviour consists of two stages with different time delays: one is of the order of 1 s and the other is of the order of 10 s. It takes about 1 s for the product water to come up on to the flow channel surface so that oxygen supply is temporarily blocked, which causes voltage loss in that “undershoot”. The correlation of dynamic behaviour with stoichiometry and cathode flooding is analyzed from the results of these experiments.
Jyyoung Jyoung - One of the best experts on this subject based on the ideXlab platform.
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analysis of Transient Response of a unit proton exchange membrane fuel cell with a degraded gas diffusion layer
2011Co-Authors: Junhyun Cho, Kyoungdoug Min, Jaeman Park, Hansang Kim, Eunsook Lee, Jyyoung JyoungAbstract:The Transient Response characteristics and durability problems of proton-exchange membrane fuel cells are important issues for the application of PEM fuel cells to automotive systems. The gas diffusion layer is the key component of the fuel cell because it directly influences the mass transport mechanism. In this study, the effects of GDL degradation on the Transient Response of the PEM fuel cell are systematically studied using Transient Response analysis under different stoichiometric ratios and humidity conditions. With GDLs aged by the accelerated stress test, the effects of hydrophobicity and structural changes due to carbon loss in the GDL on the Transient Response of PEM fuel cells are determined. The cell voltage is measured according to the sudden current density change. The degraded GDLs that had uneven hydrophobicity distributions cause local water flooding inside the GDL and induce lower and unstable voltage Responses after load changes.
