The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
J. P. Zheng - One of the best experts on this subject based on the ideXlab platform.
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High Energy Density Electrochemical Capacitors Without Consumption of Electrolyte
Journal of The Electrochemical Society, 2009Co-Authors: J. P. ZhengAbstract:We proposed an electrochemical capacitor that consists of a battery/double-layer capacitor or a pseudocapacitor/pseudocapacitor electrode configuration, with charge transferring during the charge and discharge processes. This is fundamentally different from exiting Capacitors including conventional double-layer electrochemical Capacitors and asymmetrical cells. The ions in the proposed Capacitors are shuttled between two electrodes during the charge and discharge cycle. The theoretical energy density of the proposed asymmetric Capacitors is as high as 60 W h/kg vs less than 15 and 25 W h/kg for conventional double-layer Capacitors and battery/double-layer Capacitors, respectively. © 2009 The Electrochemical Society.
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The Limitations of Energy Density for Electrochemical Capacitors
Journal of The Electrochemical Society, 1997Co-Authors: J. P. ZhengAbstract:Electrochemical Capacitors can be divided into two types depending on whether the salt concentration in the electrolyte changes during charging and discharging. In the first type of capacitor, such as double-layer Capacitors, the salt concentration in the electrolyte reduces during the charging of the capacitor. The maximum energy density of this type of capacitor will depend not only on the specific capacitance and the operating voltage, but also on the salt concentration of the electrolyte. In this paper, a formula describing the dependence of energy density on specific capacitance, operating voltage, and salt concentration is given based on the optimized weight (or volune) ratio of the electrode material and the electrolyte. It shows that for electrochemical Capacitors using nonaqueous electrolytes, the maximum energy density of the capacitor will be limited mainly by the low salt concentrations of the electrolyte. The relationship between the energy density and the mass density of the electrode is also given. The optimum mass density of the electrode can be obtained based on the value of the theoretical energy density for Capacitors with different electrolytes. In the second type of capacitor, such as pseudoCapacitors with metal oxide electrodes, the salt concentration in the electrolyte remains constant during charging and discharging. The maximum energy denisty of this type of capacitor will be limited mainly by specific capacitance and operating voltage.
Kevin Lee - One of the best experts on this subject based on the ideXlab platform.
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Stability analysis and improvement of V/Hz controlled adjustable speed drives equipped with small DC-link thin film Capacitors
2018 IEEE Applied Power Electronics Conference and Exposition (APEC), 2018Co-Authors: Zhentian Qian, Wenxi Yao, Kevin LeeAbstract:Due to thin film capacitor's enhanced reliability and improved input current harmonic performance, adjustable speed drives (ASDs) without using electrolytic dc-link Capacitors have been researched extensively in recent years. However, because of challenging stability and motor control issues associated with small thin film based dc-link Capacitors, in depth studies on a V/Hz controlled ASD cannot be found in publications. In this paper, a state space model, taking into account the dc-link choke, the thin film dc-link capacitor as well as the inverter switching dead-time effect, is developed to analyze the stability of such a system. Instability is quantified analytically. A novel active damping method is proposed to improve the overall system stability. The accuracy of the model and the effectiveness of the active damping method are verified through experimentation using a 3% thin film capacitor on a 2.2kW, 380V, 50Hz setup.
Jaesik Chung - One of the best experts on this subject based on the ideXlab platform.
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Lithium-ion Capacitors: Electrochemical performance and thermal behavior
Journal of Power Sources, 2013Co-Authors: Patricia H. Smith, Thanh N. Tran, Thomas L. Jiang, Jaesik ChungAbstract:We report on the electrochemical performance of 500 F, 1100 F, and 2200 F lithium-ion Capacitors containing carbonate-based electrolytes. First and second generation lithium-ion Capacitors were cycled at temperatures ranging from −30 °C to 65 °C, with rates from 5 C to 200 C. Unlike acetonitrile-based electric double-layer Capacitors, whose performance has been reported to be relatively insensitive to temperatures between −30 °C and 40 °C, lithium-ion capacitor performance degrades at low temperatures and displays characteristics typical of a lithium-ion battery. Three-electrode lithium-ion capacitor cycling tests revealed that reduced capacity at low temperatures is due to the polarization of the lithiated, negative electrode. The self-discharge of cells at the various temperatures was studied and compared to an electric double-layer capacitor and a lithium-ion battery cell. Lithium-ion Capacitors and batteries were observed to have significantly lower self-discharge rates than electric double-layer Capacitors. Accelerating rate calorimetry and differential scanning calorimetry were used to assess the thermal runaway behavior of full cells along with the thermal properties of the cell components. Our study showed that the thermal behavior of the lithium-ion capacitor is in between those of an electric double-layer capacitor and a lithium-ion battery.
Zhentian Qian - One of the best experts on this subject based on the ideXlab platform.
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Stability analysis and improvement of V/Hz controlled adjustable speed drives equipped with small DC-link thin film Capacitors
2018 IEEE Applied Power Electronics Conference and Exposition (APEC), 2018Co-Authors: Zhentian Qian, Wenxi Yao, Kevin LeeAbstract:Due to thin film capacitor's enhanced reliability and improved input current harmonic performance, adjustable speed drives (ASDs) without using electrolytic dc-link Capacitors have been researched extensively in recent years. However, because of challenging stability and motor control issues associated with small thin film based dc-link Capacitors, in depth studies on a V/Hz controlled ASD cannot be found in publications. In this paper, a state space model, taking into account the dc-link choke, the thin film dc-link capacitor as well as the inverter switching dead-time effect, is developed to analyze the stability of such a system. Instability is quantified analytically. A novel active damping method is proposed to improve the overall system stability. The accuracy of the model and the effectiveness of the active damping method are verified through experimentation using a 3% thin film capacitor on a 2.2kW, 380V, 50Hz setup.
Philippe Lataire - One of the best experts on this subject based on the ideXlab platform.
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Methods of modeling and identifying the electrical characteristics of super capacitor energy storages
International Review of Electrical Engineering, 2008Co-Authors: Yonghua Cheng, J.a Van Mierlo, Philippe LataireAbstract:Super capacitor energy storages have very high power density and low energy density in comparison with battery energy storages. So it is important to well configure the super capacitor energy storage as peak power unit. In this case, the simple and accurate model of super Capacitors is required. Therefore, the methods of modeling and identifying the electrical characteristics of super Capacitors are proposed in this paper. Based on the detected parameters, the modeling of super Capacitors is evaluated both in simulation system and in the test setup of a dedicated passenger car in ECE15 cycle. Finally the methods of identifying and balancing voltage difference of super capacitor energy storage are also presented, which can ensure high available energy capacity and long life time of super Capacitors. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved.
