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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Evaluation of the constant potential method in simulating electric double-layer capacitors

A major challenge in the molecular simulation of electric double layer capacitors (EDLCs) is the choice of an appropriate model for the electrode. Typically, in such simulations the electrode surface is modeled using a uniform fixed charge on each of the electrode atoms, which ignores the electrode response to local charge fluctuations in the electrolyte solution. In this work, we evaluate and compare this Fixed Charge Method (FCM) with the more realistic Constant Potential Method (CPM), [S. K. Reed et al., J. Chem. Phys. 126, 084704 (2007)], in which the electrode charges fluctuate in order to maintain constant electric potential in each electrode. For this comparison, we utilize a simplified LiClO{sub 4}-acetonitrile/graphite EDLC. At low potential difference (ΔΨ ⩽ 2 V), the two methods yield essentially identical results for ion and solvent density profiles; however, significant differences appear at higher ΔΨ. At ΔΨ ⩾ 4 V, the CPM ion density profiles show significant enhancement (over FCM) of “inner-sphere adsorbed” Li{sup +} ions very close to the electrode surface. The ability of the CPM electrode to respond to local charge fluctuations in the electrolyte is seen to significantly lower the energy (and barrier) for the approach of Li{sup +} ions to the electrode surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A Review of Degradation Behavior and Modeling of Capacitors

This paper firstly reviews the failure causes, modes and mechanisms of two major types of capacitors used in power electronic systems - metallized film capacitors and electrolytic capacitors. The degradation modeling related to these capacitors is then presented. Both physics-of-failure and data-driven degradation models for reliability and lifetime estimation are discussed. Based on the exhaustive literature review on degradation modeling of capacitors, we provide a critical assessment and future research directions.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2021

Analytical Expression for DC Link Capacitor Current in a Cascaded H-Bridge Multi-Level Active Front-End Converter

Medium-voltage grid-tied systems often use a cascaded H-bridge multi-level active front-end. In this converter, dc link bus capacitors play an important role in stabilizing the converter and enabling both active and reactive power injections. The present work provides analytical expressions for the capacitor current, which are essential for optimizing system design (especially capacitor size vs. lifetime). Then, the expression is incorporated into the grid connected bidirectional power system model. Consequently, this work contributes to the guiding principles to choose accurate dc link capacitor ratings against grid-side power delivery requirements. The analytical results have been validated with detailed simulations and hardware results.

cascaded H-bridge, carrier-based PWM, dc-link capa↗
DOE OSTI2020

Transient pulse‐based impedance characterisation of DC‐link capacitor for EV systems

In this study, a method for impedance characterisation of DC‐link capacitors based on transient pulse analysis is proposed. The fundamentals of the concept are presented and design considerations are discussed. The functionality of the proposed approach is supported by SPICE simulation with two different commercial capacitors from different manufacturers and validated with experimental results. Experimental results for equivalent series resistance, equivalent series inductance (ESL) and capacitance estimation are presented for commercial DC‐link capacitors and compared with component analyser results. The simulation and experimental results show that the proposed method is a promising candidate for capacitance and ESL estimation of capacitors in EV traction systems.

Gurpinar, Emre↗
DOE OSTI2019

Capacitive deionization charge transfer from one capacitor simultaneously to multiple capacitors

An energy transfer system is disclosed which has a controller, a first capacitor acting as a first electrode, a second capacitor acting as a second electrode, a first inductor for storing energy received from the first capacitor, and transferring the stored energy to the second capacitor, and a first plurality of electronic switches. The first plurality of electronic switches may be controlled by the controller to control a transfer of energy from the first capacitor to the first inductor, and from the first inductor to the first capacitor. An additional energy transfer subsystem may be included which has a second inductor for receiving energy from the first capacitor while the first inductor is transferring the stored energy to the second capacitor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Dynamic Wireless Charging of Electric Vehicle Demonstrated at Oak Ridge National Laboratory: Benefit of Electrochemical Capacitor Smoothing

Abstract Wireless charging of an electric vehicle while in motion presents challenges in terms of low latency communications for roadway coil excitation sequencing, and maintenance of lateral alignment, plus the need for power flow smoothing. This paper summarizes the experimental results on power smoothing of in-motion wireless EV charging performed at Oak Ridge National Laboratory using various combinations of electrochemical capacitors at the grid-side and in-vehicle. Electrochemical capacitors of the symmetric carbon-carbon type from Maxwell Technologies comprised the in-vehicle smoothing of wireless charging current to the EV battery pack. Electro Standards Laboratories fabricated the passive and active parallel lithium-capacitor unit used to smooth grid-side power. Power pulsation reduction was 81% on grid by LiC, and 84% on vehicle for both lithium-capacitor and the carbon ultracapacitors.

Miller, John M↗
DOE OSTI2018

Multilayer capacitors, method for making multilayer capacitors

The invention provides a stacked capacitor configuration comprising subunits each with a thickness of as low as 20 microns. Also provided is combination capacitor and printed wire board wherein the capacitor is encapsulated by the wire board. The invented capacitors are applicable in micro-electronic applications and high power applications, whether it is AC to DC or DC to AC, or DC to DC.

42 ENGINEERING↗
DOE OSTI2018

Wound/stacked ceramic film capacitors, method for making ceramic film capacitors

The invention provides a process for making ceramic film capacitors, the process comprising supplying a flexible substrate, depositing a first electrode on a first region of the flexible substrate, wherein the first electrode defines a first thickness, overlaying the first electrode with a dielectric film; and depositing a second electrode on the ceramic film, wherein the second electrode defines a second thickness. Also provided is a capacitor comprising flexible substrate, a first electrode deposited on said flexible substrate, a dielectric overlaying the first electrode; and a second electrode deposited on said dielectric.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Self-activation of cellulose: A new preparation methodology for activated carbon electrodes in electrochemical capacitors

Current synthetic methods of biomass-derived activated carbon call for a costly chemical or physical activation process. Herein, we report a simple one-step annealing synthesis yielding a high surface area cellulose-derived activated carbon. We discover that simply varying the flow rate of Argon during pyrolysis enables ‘self-activation’ reactions that can tune the specific surface areas of the resulting carbon, ranging from 98 m2/g to values as high as 2600 m2/g. Furthermore, we, for the first time, observe a direct evolution of H2 from the pyrolysis, which gives strong evidence towards an in situ self-activation mechanism. Surprisingly, the obtained activated carbon is a crumbled graphene nanostructure composed of interconnected sheets, making it ideal for use in an electrochemical capacitor. The cellulose-derived nanoporous carbon exhibits a capacitance of 132 F g-1 at 1 A g-1, a performance comparable to the state-of-the-art activated carbons. This work presents a fundamentally new angle to look at the synthesis of activated carbon, and highlights the importance of a controlled inert gas flow rate during synthesis in general, as its contributions can have a very large impact on the final material properties.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

A combined capacitance-voltage and hard x-ray photoelectron spectroscopy characterisation of metal/Al{sub 2}O{sub 3}/In{sub 0.53}Ga{sub 0.47}As capacitor structures

Capacitance-Voltage (C-V) characterization and hard x-ray photoelectron spectroscopy (HAXPES) measurements have been used to study metal/Al{sub 2}O{sub 3}/In{sub 0.53}Ga{sub 0.47}As capacitor structures with high (Ni) and low (Al) work function metals. The HAXPES measurements observe a band bending occurring prior to metal deposition, which is attributed to a combination of fixed oxide charges and interface states of donor-type. Following metal deposition, the Fermi level positions at the Al{sub 2}O{sub 3}/In{sub 0.53}Ga{sub 0.47}As interface move towards the expected direction as observed from HAXPES measurements. The In{sub 0.53}Ga{sub 0.47}As surface Fermi level positions determined from both the C-V analysis at zero gate bias and HAXPES measurements are in reasonable agreement. The results are consistent with the presence of electrically active interface states at the Al{sub 2}O{sub 3}/In{sub 0.53}Ga{sub 0.47}As interface and suggest an interface state density increasing towards the In{sub 0.53}Ga{sub 0.47}As valence band edge.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗