Ac Capacitance Research Articles

Dendrite‐Free Zn Anode Modified with Prussian Blue Analog for Ultra Long‐Life Zn‐Ion Capacitors

AbstractThe main challenge for aqueous zinc‐ion capacitors is the low stability of zinc anode. In this study, a Prussian blue analog (PBA) has been coated on the surface of zinc foil to create an inorganic protective layer. This layer features a three‐dimensional open microporous structure, which not only endows it with excellent pseudocapacitive properties but also serves as an effective barrier against dendrite growth. The presence of PBA coating can increase the nucleation point of zinc ions and provide a low‐energy barrier for the rapid migration of zinc ions. Hence, the PBA@Zn ||PBA@Zn symmetric cell exhibits exceptional cycling stability, enduring over 1400 h of operation at a current density of 1 mA cm−2 and a capacity of 1 mAh cm−2. The PBA@Zn||AC capacitor demonstrated a discharge capacity of 46.23 mAh g−1 after 10 000 cycles at a current density of 1 A g−1, with a capacity retention of 92.41%, whereas the discharge capacity of Zn||AC capacitor is only 16.02 mAh g−1, with a capacity retention of 23.13%. The PBA@Zn||AC capacitor exhibited remarkable endurance and stability, retaining a substantial discharge capacity of 32.7 mAh g−1 after 10 000 cycles at 10 A g−1. Density Functional Theory (DFT) calculations also show that PBA has a strong interaction with Zn and exhibits superior zincophilic ability. This study reports industrially applicable low‐cost Prussian blue analogs as artificial interfacial protective layers for improving the cycling stability of zinc anode with a low‐energy barrier for rapid migration of zinc ions especially at high current density.

Polypyrrole functionalized cellulose/polypropylene composite membrane with zinc inducing and dendrite resistance for robust zinc-ion batteries

Dendrite growth and subsequent membrane puncture stemming from uneven deposition of zinc ions pose a significant challenge for aqueous zinc ion batteries (AZIBs). Herein a polypyrrole functionalized cellulose/polypropylene (PPy-cellulose/PP) composite membrane with promising zinc inducing and dendrite resistance was rationally designed through an in-situ polymerization strategy to enable robust zinc-ion batteries. Experimental data and theoretical simulations reveal that a continuous conducting network, constructed by PPy nanoparticles, could homogenize the electric field and reduce the interfacial resistance of zinc anode. Moreover, the zincophilic nitrogen-containing functional groups in PPy induced the migration and deposition of zinc ions uniformly. The combination of polypropylene laminate enhanced the puncture resistance and mechanical strength of the composite membranes. Consequently, Zn||Zn symmetric cell assembled with the PPy-cellulose/PP composite membrane exhibited stable cycling performance over 2000 h at 0.5 mA cm−2/0.5 mAh cm−2. Further verification was conducted on the practical application of PPy-cellulose/PP membranes in Zn||MnO2 full cells and Zn||AC capacitors. Notably, a high capacity retention of 89.6 % was achieved for the Zn||AC capacitor after 10,000 cycles at 1 A g−1. The new design of PPy functionalized cellulose/polypropylene membranes provides a valuable protocol to stabilize zinc anodes for zinc-ion batteries.

A three-dimensional zincophilic layer for dendrite-free zinc metal anodes

Aqueous zinc ion battery is a promising next-generation energy storage device with high safety, low cost and environmental friendliness. However, the dendrite growth caused by uneven deposition of zinc ions and the corrosion of electrolyte on the electrode seriously shorten the cycle life of Zn anode. In this work, a three-dimensional zincophilic layer modified Zn anode (PZ-8@Zn) was prepared by electrospinning method to compound the zeolitic imidazolate framework-8 (ZIF-8) in polyacrylonitrile fiber. The coating of three-dimensional fiber layer enhances the corrosion resistance of the electrode and reduces the local current density, thus inhibiting the generation of Zn dendrites. The zincophilic ZIF-8 is beneficial to accelerate the zinc ion deposition kinetics on the electrode surface and reduce the nucleation barrier of Zn. Therefore, the PZ-8@Zn||PZ-8@Zn symmetric cells exhibits satisfactory rate performance and cycle stability, with a low overpotential of 69 mV after cycling at 3 mA cm−2 for 800 h. The PZ-8@Zn||AC capacitor has a large specific capacity of 86.1 mAh g−1 after 1000 cycles at 1 A g−1. This work provides a method to construct zinc ion deposition channels to obtain dendrite-free zinc anodes.

An Edge-based Condition Monitoring Scheme for the AC and DC capacitors in LLC Converter

An Edge-based Condition Monitoring Scheme for the AC and DC capacitors in LLC Converter

Carbon-graphene-epoxy sandwich dielectric for improved dielectric response to humidity

A sandwich structure of carbon-epoxy laminate with graphene nanoplatelets is used for increasing the AC conductivity, dielectric constant and sensitivity towards moisture. The Quasi Fickian distribution of moisture absorption of epoxy is retained with the inclusion of carbon fibers and graphene nanoplatelets of 1 weight percent. The effect of relative humidity (RH) over a range of 30–90% on AC conductivity and capacitance has been investigated. Use of carbon fibers with graphene nanoplatelets significantly enhances the electrical conductivity and dielectric constant as compared to carbon-epoxy laminate without graphene nanoplatelets. The two parameters reveal linear dependence on humidity in the low frequency range of 100–1000 Hz. The AC conductivity increases at the rate of 2 nSm−1/% RH in laminate with carbon fiber and it increases to 50 nSm−1/%RH with the incorporation of graphene nanoplatelets. The increase in AC conductivity from 100 Hz to 1000 Hz is in the range of 0.1 to 0.2 μS/m with carbon fibers and it increases from 1 to 4 μS/m with the inclusion of graphenenanoplatelets. Increase is AC conductivity from 1 kHz to 10 MHz is by five orders of magnitude, with a steep increase around 5 MHz in both laminates. The incorporation of graphenenanoplatelets helps to increase the dielectric constant by 2.4–2.8 times as compared to epoxy with carbon fiber. The swelling in the laminates estimated after 96 h of exposure to 90% RH is observed to be less than 0.05%. The use of graphenenanoplatelets improves moisture sensitivity of the carbon-epoxy laminate.

A Unified Capacitor Stress Emulation Method for High-Power Converter Applications

This paper proposes a unified capacitors stress emulation method, which has two unique test capabilities: 1) concurrent electrical stress emulation to AC capacitors and DC capacitors; 2) different electrical stress levels (including different ripple current, ripple voltage, and DC voltage) can be individually controlled for the testing samples. It preserves the advantages of a recently reported method with a minimum required power supply and is robust to testing sample degradation. This method is suitable for application-oriented stress emulation testing with different types of DC / AC capacitors and multiple electrical stresses in high power converter systems. The circuit architecture and testing ability of this method are presented. Moreover, analytical models are derived to size the key components to realize various testing requirements. Proof-of-concept experimental results are presented to verify the feasibility of the proposed test method.

One-step and real-time detection of Hg2+ in brown rice flour using a biosensor integrated with AC electrothermal enrichment.

Mercury (Hg2+) is one of the most toxic heavy metals in farm products, so rapid detection of trace Hg2+ has always been sought after with high interest. Herein, we report a biosensor to specifically recognize Hg2+ in leaching solutions of brown rice flour. This sensor is simple and of low cost, with a very short assay time of 30s. Another merit is the ultra-low limit of detection (LOD) at fM level. In addition, the specific aptamer probe realizes a good selectivity above 105: 1 against the interferences. This sensor is developed based on an aptamer-modified gold electrode array (GEA) for capacitive sensing. Alternating current electrothermal (ACET) enrichment is induced during the AC capacitance acquirement. Thus, the enrichment and detection are coupled as a single step, and pre-concentration is needless. Owing to the sensing mechanism of solid-liquid interfacial capacitance and ACET enrichment, Hg2+ level can be sensitively and rapidly reflected. Also, the sensor has a wide linear range from 1 fM to 0.1nM and a shelf life of 15days. This biosensor shows advantages on overall performance, enabling easy-to-operate, real-time, and large-scale Hg2+ detection in farm products.

Modeling and Suppression of Zero-Sequence Circulating Current Resonance for Parallel Interleaved Inverters With Bypass Capacitor-Based Leakage Current Mitigation

Connection of the neutral point of the ac capacitor to the midpoint or positive (negative) rail of the dc link is a cost-effective method to suppress the leakage current to ground. However, applying it to a modular parallel interleaved inverter system with the common ac and dc bus will induce zero-sequence circulating current (ZSCC) resonance issue. This paper firstly establishes the common mode equivalent circuit model of the multi-parallel inverters system. Secondly, the generation mechanism of ZSCC resonance is investigated based on the installed impedance model. To guarantee the stable operation, the resonance suppression method which combines the sampling instant shift and phase lag compensation is proposed. The frequency aliasing phenomenon and resultant ZSCC dc offset issue due to the sampling instant shift are further analyzed, and an effective suppression scheme of the ZSCC dc offset is proposed by adding an additional ZSCC dc offset control loop. Finally, the comparative experiments verify the effectiveness of the proposed method.

Sensorless AC Capacitor Voltage Monitoring Method for HAPF

This study presents a method for monitoring the voltage across the AC capacitor in a grid-connected hybrid active power filter without the use of additional voltage sensors. In the case of an AC capacitor used in a hybrid, active power filter, there is a risk of burnout caused by exceeding the allowable voltage owing to the harmonic current and voltage generated by the inverter. Therefore, this study presents a method to monitor the voltage of the AC capacitor using the current from which the DC component has been removed without any additional voltage sensors to prevent the burn-out of the AC capacitor. The proposed sensorless AC capacitor voltage monitoring method is verified through simulations and experiments. The difference between the magnitude of the voltage measured in the simulations and experiments and the magnitude of the voltage predicted with the proposed method was approximately 0.526[%] on average.

Study on Capacitance Properties of Redox Ion Doped Zn-Based Electrode Materials

Metal oxide electrode materials have relatively high theoretical capacitance. However, structure, morphology and composition of this kind of materials have significant influence on electrochemical performance. Moreover, metal oxide electrode materials have problems of low power density and cyclic stability. In this work, Mo-doped hydroxide zinc carbonate material (Mo-HZC) is synthesized on foam Ni surface by hydrothermal method. This Mo-doping electrode exhibits typical pseudocapacitance. Specific capacitance of Mo-HZC in 1.0 mol L-1 KOH is 698.9 F g-1 (1.0 A g-1), which is 2.5 times that of the undoped sample. The maximum energy density and power density of Mo-HZC electrode are 32.1 WH kg-1 and 3.16 KW kg-1, respectively. Assembled Mo-HZC//AC capacitor exhibits a long-term cycling performance with remains 79.5% capacitance retention within 20 000 cycles at 1.0 A g-1.

Binder-Free Fe<sub>2</sub>O<sub>3</sub>- C-Ni Composite for Supercapacity Eletrode

Fe2O3-C-Ni heterojunction structured composite on foam Ni was successfully prepared by simple and effective hydrothermal reaction. The obtained material had good structural stability and excellent electrical conductivity. This binder-free Fe2O3-C-Ni electrode exhibits typical pseudocapacitance. Specific capacitance of Fe2O3-C-Ni in 1.0 mol L-1 KOH reaches 844.6 F g-1, which is higher than that of Fe2O3-Ni and C-Ni electrodes. For practice application, assembled Fe2O3-C-Ni//AC capacitor exhibits a long-term cycling performance with remains 79.5% capacitance retention within 20000 cycles at 1 A g-1.

Large Signal Stability Criteria Combined with a 3D Region of Asymptotic Stability Method for Islanded AC/DC Hybrid Microgrids

Large disturbances frequently happen in isolated AC/DC Hybrid Microgrids. Unfortunately, constant power loads (CPLs) with negative impedance characteristics are equivalent to positive feedback, resulting in an increase in large disturbances. The system can easily become unstable. Consequently, large signal stability criteria are proposed in this paper. Combined with a three-dimensional region of asymptotic stability (3D RAS) method for islanded AC/DC Hybrid Microgrids, important parameters to increase stability margins were determined. Firstly, mixed potential theory was used to derive a large-signal stability criterion. The criteria gave constraints on filtering parameters, CPL power, power of the battery to charge and discharge, AC resistive loads, and DC bus voltage. Then, Lyapunov functions were constructed, and the Lasalle invariance principle was adopted to achieve 3D RAS. When large disturbances emerged, and simultaneously voltage and current varied in 3D RAS, the system always obtained stability and reached new steady-state equilibrium points. Finally, according to comparisons, bigger capacitances of the DC bus capacitor and the AC capacitor, larger battery discharging power and smaller charging power could significantly increase stability margins of islanded Microgrids. Simulations and experimental data have shown that the large signal stability criteria and the 3D RAS work.

A Proposed R-T Model for Atmospheric Corrosion of Metallized Film in AC Capacitors

Atmospheric corrosion is a significant issue affecting the storage quality of metallized film capacitors (MFCs). Oxygen and moisture in the atmosphere permeate among the layers in capacitor, initiating oxidation on the surface of metal layer, which increases the electrode resistance. In this work, a resistance–time model is proposed to study the atmospheric corrosion mechanism of nano-scaled Al–Zn metal layer. The analysis results point out that it is the barrier of metal–oxide interface that affects the anticorrosion ability. Moreover, the metal composition is studied as a factor influencing the anticorrosion ability, revealing that the enhancement gained by adjusting the composition tends to saturate once the Al content exceeds 10 wt.%. Therefore, in terms of MFCs for ac applications, the Al content in electrode should be controlled within 10 wt.% as a compromise between the atmospheric and electrochemical corrosion.

Modern structure and innovative efficiency of special equipment for analyzing semiconductor devices

The multimeter is a sophisticated electronic measuring device that combines several functions: voltmeter, ammeter and ohmmeter. It measures DC and AC voltage, DC and AC current, resistance, capacitance, frequency, transistor gain, diode checks and wire-check connections. The multimeter also features automatic polarity reversal. Digital multimeters range from 2.5 digits (simple devices) to 3.5 digits (most devices). Slightly more expensive instruments with 4.5, 5 and higher digits are also available. The digit capacity “3.5”, for example, means that the display of the device shows 3 full digits, with a range of 0 to 9, and 1 digit with a limited range, i.e., the device can give readings in the range of 0.000 to 1.999; if the measured value is outside these limits, a changeover to another range is required. Many multimeters now have other functions available. This paper is relevant and can be useful because the multimeter is a lightweight, portable device that is convenient for basic measurements and troubleshooting in hard-to-reach places, as well as being a sophisticated stationary device with many features. Multimeter (from multimeter, tester from test, Avometer from AmperVoltOhmMeter) is a combined electrical measuring device that combines several functions. In the minimum set is a voltmeter, ammeter and ohmmeter. Sometimes a multimeter is performed in the form of current clamps. There are digital and analog multimeters. device multimeter computing technique.

A Multifunction Freestanding Liquid-Solid Triboelectric Nanogenerator Based on Low-Frequency Mechanical Sloshing.

A simple rectangular-structured freestanding liquid-solid triboelectric nanogenerator (LS-TENG) was fabricated, which used fluorinated ethylene propylene (FEP) films and deionized water (DI) as friction materials. The LS-TENG can effectively convert mechanical energy into electrical energy under the extremely low-frequency shaking of 2 Hz and shows greatly reliable stability. The influence of liquid volume and units on the output performance of the LS-TENG was studied, and the mechanism of the triboelectric electrification process of the LS-TENG was analyzed by COMSOL Multiphysics software. The results show that friction materials, liquid types, and number of units have a great effect on the output performance of the LS-TENG. Under the optimized conditions, the designed array LS-TENG shows high output performance with the open-circuit voltage, short-circuit current, and transferred charge of 120 V, 3.9 μA, and 133 nC, respectively. The LS-TENG can be applied in capacitive storage, AC power, signal acquisition, and self-powered sensor. The multifunctional LS-TENG provides a potentially practical route for harvesting low-frequency mechanical energy in natural environments and enabling multifunctional applications.

Nonthermal Plasma Multi-Reactor Scale-Up Using Pulse Capacitive Power Supplies

The scale up of nonthermal plasma (NTP) reactors requires the simultaneous operation in parallel of a large number of units supplied from the same power supply. The present paper aims to demonstrate the feasibility of parallel operation of multiple mini-NTP reactors. In order to demonstrate the parallel operation of a large number of NTP reactors, three different types of power supplies are considered. In addition to the most simple and common solution, which involves the use of individual, independent power supply for each reactor (an ignition coil driven by a pulse generator), two other configurations of supplies (capacitive AC and capacitive DC), simpler and less expensive, are tested. The capacitive pulsed power supplies allow the generation of HV pulses by an AC power supply (usually an AC transformer), as well as by a DC power supply using an R–C circuit. For the DC resistive–capacitive configuration, the frequency can be adjusted. For all configurations, the power of the discharge can be modified by changing the value of capacitors or resistors. The feasibility of the proposed systems was demonstrated by assessing the concentration of hydrogen peroxide induced in water after plasma treatment. The obtained results reveal that the proposed capacitive AC and DC power supplies allow a large number of plasma reactors to operate in parallel independently.

Continuous Ion Separations Using Non-Faradaic Capacitive AC Ratcheting

Traditional electrochemical separations processes require Faradaic reactions for sustained currents. We discovered that this limitation can be overcome by oscillating the applied potential across an ion-permeable material that has an asymmetric electric potential profile. We demonstrated this phenomenon for the first time using a flashing ratchet consisting of a nanoporous anodized aluminum oxide membrane infiltrated with salt water and containing metallic contacts on either side. When a symmetric +/-300 mV square-wave potential was applied to the metallic contacts at a frequency of ~100 Hz, an open-circuit potential as large as ~50 mV was observed between Ag/AgCl electrodes immersed in the chloride-containing electrolyte and positioned across the membrane. While this open-circuit potential was determined to be a consequence of net ionic polarization, additional electrochemical data were also consistent with transport of neutral salt across the membrane via a proposed ambipolar transport mechanism. In comparison, application of a DC potential bias resulted in non-Faradaic charging, and a near-zero long-time open-circuit potential. Moreover, high ionic strengths and large pore sizes diminished ratcheting behavior, consistent will more complete screening of surface charges in the nanopores. Collectively, this work represents a new paradigm for direct ion pumping and salt separations that requires no Faradaic reactions or additional transport pathway for ions or electrons.

Optimal Switching-Sequence-Based Model Predictive Control for a Hybrid Multilevel STATCOM

In this article, we introduce a model predictive control with optimal switching sequence (OSS-MPC) for a multilevel static synchronous compensator (STATCOM). The studied STATCOM is based on a hybrid multilevel inverter named HC-FNPC formed by the cascaded connection of H-bridge cells with a full-bridge neutral point clamped cell (FNPC). In this article, the optimal switching sequences are derived for HC-FNPC STATCOM by considering the impact of each switching sequence on the voltage of capacitors. Then, the control objectives of hybrid multilevel STATCOM, i.e., ac current control and capacitors’ voltages balancing, are formulated in terms of OSS-MPC for the first time. In contrast to the conventional MPC, this method provides a fixed-switching frequency. Also, by a combination of optimal switching sequences in MPC, the regulation of capacitors’ voltages with unequal values is realized. The control system's performance is verified on a nine-level (9L) 2.4 Mvar/11 kV HC-FNPC STATCOM in MATLAB/Simulink. Also, the experimental results are provided on a 9L 1.25 kvar/220 V scaled-down hardware prototype.

A Robust Testing Method for DC and AC Capacitors With Minimum Required Power Supply

This letter proposes a testing method to emulate realistic stress conditions of dc and ac capacitors, with minimum required power supply and robust operation at the presence of capacitor degradation. It is especially suitable for parameter characterization and accelerated degradation testing of high-voltage and high-ripple current power electronic capacitors. The circuit architecture of the proposed testing method and the constraints of the testing samples under given designs are discussed. Proof-of-concept experiments on both dc and ac capacitors verify the feasibility.

Electrical resistance and capacitance responses of smart ultra-high performance concrete with compressive strain by DC and AC measurements

Electrical properties and strain self-sensing ability of smart ultra-high performance concrete (UHPC) containing different steel fiber concentrations were characterized using DC resistivity, AC resistivity, and capacitance measurements. Four-probe DC resistance measurement and four-probe/ two-probe AC impedance measurement were performed in this study. The resistivity measured by the two-probe AC method is lower than that measured by the four-probe DC method. The magnitude of impedance measured by the four-probe method is close to that measured by the two-probe method. The capacitance of UHPC increases with an increase in fiber dosages, which is mainly related to the interfacial polarization, including the polarization of solid–liquid electrical double layer and fiber/matrix/fiber interfacial polarization. The addition of steel fibers can effectively improve the sensitivity of AC resistance and capacitance variation with strain, but it has less effect on the sensitivity of DC resistance variation with strain, which is due to different strain self-sensing mechanisms. Thus, the sensitivity represented by AC resistance and capacitance is higher than that represented by DC resistance. UHPC with the steel fiber content of 1.5% exhibits high sensitivity and good linear relationship between the fractional change in AC electrical parameters and strain. The results indicate that AC resistance measurement is preferable to be adopted for strain self-sensing using smart UHPC.