Capacitance Standards Research Articles

Cooling performance enhancement of electric vehicle film capacitor for ultra-high temperatures using micro-channel cold plates thermal management system

The increasing voltage and power density demands of electric vehicles pose notable challenges to the high-temperature resistance performance of film capacitors within motor controllers. Existing methods primarily focus on material modifications and conventional thermal management designs, often tested at 85 °C, which fail to meet the escalating demands for high-temperature operations. This paper presents the design and optimization of a thermal management system for film capacitors through simulations and experiments under ultra-high temperatures. ANSYS electro-thermal coupled simulation was used to analyze the temperature distribution of the capacitor under different ripple currents, leading to the development of a thermal management system based on internal micro-channel cold plates (IMCPs). These IMCPs were optimized using response surface and genetic algorithms to enhance cooling performance. Experimental and simulation comparisons were made between standard capacitors and those with IMCPs under ripple currents of 120 A and 180 A at 85 °C. Further examinations were conducted at ultra-high temperatures of 125 °C and 140 °C with a ripple current of 180 A. The findings show that capacitors with IMCPs had average temperature reductions of 45.50 °C and 48.45 °C at 85 °C under 120 A and 180 A ripple currents, respectively. Additionally, standard capacitors developed cracks or exploded at 125 °C and 140 °C under 180 A ripple current, while capacitors with IMCPs maintained normal functionality. These results indicate that capacitors integrated with IMCPs meet the rigorous high-temperature operational standards required for motor controllers in high-voltage electric vehicles.

The evaluation of the long-term drift of electrical capacitance measurement standards by two methods

Measurements of electrical capacitance are essential in various fields of electrical engineering, electronics and other fields. Capacitance measurements are necessary for correct design of electrical circuits and devices. Such measurements help ensure the stability and reliability of electrical systems such as power supplies, filters, capacitors, etc. In some applications, such as radio transmitters, filters, and other electronic devices, it is needed to maintain certain frequency characteristics. It is critical and appropriate to consider various factors related to the drift of the measuring instrument or measurement standard when performing measurements to ensure the required accuracy and reliability of the measurements. The study of the time drift of the measurement standard is mandatory when carrying out comparisons of national measurement standards. The types of the drift and main methods of its evaluation for measuring instruments and measurement standards between their calibrations were analysed. A conventional method of the long-term drift analysis involves the use of regression models followed by their detailed analysis. Such models are specific mathematical functions that describe theoretical values that best represent the underlying bias in the time series for the long-term drift. Exponentially Weighted Moving Average (EWMA) charts reduces the lag inherent in conventional moving averages by giving more weight to recent observations. The results of the evaluation of the long-term drift of measurement standards of electrical capacitance for high-precision calibration of measurement standards by polynomial regression diagrams and EWMA charts are given. Polynomials of the 2nd degree were sufficient to approximate the drift of electrical capacitance measurement standards under consideration. The application of EWMA charts showed greater sensitivity to drift changes over the past few years of observations compared to the regression analysis. Consistent results were obtained.

Automated Measurement System of High Accuracy for Shunt Reactors

System for automated transformer tests (ATT) enables different measurements on power transformers, from simple to the most complex, with a high degree of automation. ATT system is now expanded with modules for measurements on shunt reactors. The measurements related to shunt reactors that are covered with the system are: measurement of losses, impedance measurement, linearity test, zero impedance measurement, winding resistance measurement, temperature rise test and measurement of mutual reactance. Besides the measurement, ATT enables data analysis and report generation, all in accordance with [1,2]. Measurement of shunt reactor losses with satisfactory accuracy is a big challenge due to power factors of the reactors as low as 0,001. A system for loss measurements with high accuracy, consisting of measuring bridge, current comparator and standard capacitor is integrated into ATT. In the paper, a comparison in terms of loss measurement accuracy on shunt reactor is given for two measurement systems – a newly integrated system for shunt reactors and standard system used for transformer measurements.

Li-metal free “in aqua” lithiation and re-lithiation of protected graphite anode for 4-V class aqueous lithium-ion capacitor

Lithium-ion capacitors, typically composed of a capacitive cathode and a pre-lithiated graphite anode in non-aqueous electrolyte, are promising power sources for energy harvesting applications with higher energy densities than standard electrochemical double layer capacitors. Superior energy density can be achieved by using pseudocapacitive cathodes in an aqueous electrolyte coupled with a water-stable protected anode. Lithiation of the graphite anode is one of the performance-governing processes influencing the working voltage, energy density, and cyclability of such power sources. Here, we report an effective, time-efficient, and safe lithiation procedure without the need of lithium metal or lithium-containing compounds as electrodes. The “in aqua” electrochemical lithiation of graphite is performed by using an over-sized activated carbon cathode and the salt dissolved in the aqueous electrolyte as the source of lithium ions. Subsequently, the protected anode (LixC6 + Li) is used as the counter electrode in an aqueous hybrid supercapacitor showing ∼70 % of capacity retention after 10,000 cycles. Nonetheless, the cycle life and capacity retention of the protected anode was further extended via an “in aqua” re-lithiation process allowing a 95 % retention of the initial capacity after 10,000 galvanostatic charge/discharge cycles.

ЗМЕНШЕННЯ ВПЛИВУ ВІДХИЛЕНЬ ПАРАМЕТРІВ ГЕНЕРАТОРІВ У ПРЕЦИЗІЙНИХ КВАДРАТУРНИХ МОСТАХ

The article is devoted to solving the problem of attestation of electric capacity standards at industrial frequency. The expediency of using a quadrature bridge of alternating current to determine the parameters of standards of electric capacity at industrial frequency by comparison with the parameters of standards of active resistance was noted. The advantage of using a bridge imbalance indicator with high input impedance is shown, which consists in the possibility of reducing the influence of higher harmonics of the supply voltages. An analysis of the well-known method of reducing of measurement errors caused by the deviation of the generator parameters from the calculated ones was carried out. It is shown that the known method does not provide sufficient compensation for the influence of these errors when the deviations of the generator parameters increase, as well as when the deviations of the bridge from the balance state increase. An iterative algorithm for calculating the measured deviation of the impedance ratio of the compared standards from the nominal value is proposed. Mathematical expressions for calculating the measured quantity are given. Calculations of the components of the measurement error for different values of generator voltage deviations were carried out. Calculations were performed for two variants of generator voltage variation implementation: multiplicative voltage amplitude variation and additive voltage phase variation. The developed iterative correction method allows to reduce the specified errors to the required levels in a small number of iteration steps - in the vast majority of cases, two steps are enough. The application of the method allows obtaining high metrological characteristics with rather large deviations of the voltage ratio of bridge generators, which makes it possible to reduce hardware costs when implementing quadrature alternating current bridges for comparing capacitance and active resistance standards. References 15, figure 1, table 1.

Estimating the long-term drift of travelling measurement standards for comparisons

In metrology, it is essential to analyse the instrumental drift of measuring instruments and measurement standards. Each reference instrument is periodically calibrated according to a frequency determined by the laboratory. Calibration establishes the metrological state of the instrument on a certain date of calibration. However, it is necessary to know the state of the measuring instrument during or after the calibration.
 Reliable accounting for drift plays an important role in maintaining measurement accuracy. Otherwise, it can lead to significant measurement errors. Accounting for time drift is mandatory when conducting international comparisons of national measurement standards. The drift uncertainty can be evaluated from its history of successive calibrations. In the absence of such a history, the magnitude order of the calibration uncertainty can be estimated.
 The analysis of the long-term drift of travelling measurement standards is limited to examples of key and supplementary comparisons of measurement standards of electrical capacitance. Quite a lot of such comparisons were conducted both by the Consultative Committee for Electricity and Magnetism (CCEM) and by most of the Regional Metrology Organizations (RMOs). There are international standards and guides that describe various statistical methods of analysing the measurement results.
 For capacitance measurement standards, time drift is predictable and nearly linear. For comparisons of measurement standards, a linear model is more than often applied, as a travelling measurement standard with excellent stability characteristics is used. The consistent results have been obtained. The linear model was applied to estimate the drift of travelling measurement standards during the key and supplementary comparisons (COOMET.EM-K4, COOMET.EM-S4, and COOMET.EM-S13) of measurement standards of electrical capacitance. The estimation of the long-term drift of measurement standards of electrical capacitance as travelling measurement standards for comparisons using a polynomial regression are presented.

Photodetectors based on chemical vapor deposition or liquid processed multi-wall carbon nanotubes

Carbon nanotubes (CNTs) have attracted great interest for applications due to their unique mechanical, electronic and optoelectronic properties. The advantages of the multiple wall carbon nanotubes for optoelectronic devices like photodetectors and photodiodes are the large effective photo-collector surface as well as the possibility to tune the band gap and absorbance by controlling the growth parameters. In this work, we demonstrate two types of hybrid Multi-Wall CNTs/Si3N4/n-Si photodetectors based on ordered (produced with Chemical Vapor Deposition – CVD) and solution processed MWCNTs and evaluate their performance in UV and visual spectrum (275 nm, 655 nm). Device parameters were obtained by comparison of I–V characteristics to Schottky barrier models and C–V characteristics to standard MIS capacitor models. The role of silicon nitride layer was also examined by comparing devices with different nitride layer thickness. Focusing on the UV part of the spectrum, the solution processed device was photosensitive in the voltage range 3V–6V giving its best performance (External Quantum Efficiency - E.Q.E. 85%@275 nm) at 5V and illumination of 5 μW. The CVD processed device showed lower EQE for the same bias voltage range. Both devices showed a low performance in optical part of the spectrum compared to the corresponding one in the UV part of the spectrum. The mean optical responsivity values obtained at the UV part of the spectrum in both cases indicate that the Visible light blind MWCNT/Si3N4/n-Si system have a potential use in UV photodetector applications. In particular, solution processed devices may pave the way for cheap production of UV sensor systems.

ANN-Based Reliability Enhancement of SMPS Aluminum Electrolytic Capacitors in Cold Environments

Due to their substantial energy density and economical pricing, switching-mode power supplies (SMPSs) often utilize electrolytic capacitors. However, their ability to function at low temperatures is essential for dependable operation in several sectors, including telecommunications, automotive, and aerospace. This study includes an experimental evaluation of how well standard SMPS electrolytic capacitors operate at low temperatures. This paper investigates the suitability of standard electrolytic capacitors used in switched-mode power supplies (SMPSs) for low-temperature applications. The experimental evaluation exposed the capacitors to temperatures ranging from −5 °C to −40 °C, assessing capacitance (Cp), impedance (Z), dissipation factor (DF), and equivalent series resistance (ESR) at each temperature. The capacitor’s time-domain electrical signals were analyzed using the Pearson correlation coefficient to extract discriminative features. These features were input into an artificial neural network (ANN) for training and testing. The results indicated a significant impact of low temperatures on capacitor performance. Capacitance decreased with lower temperatures, while the ESR and leakage current increased, affecting stability and efficiency. Impedance was a valuable diagnostic tool for identifying potential capacitor failure, showing a 98.44% accuracy drop at −5 °C and 88.75% at the peak temperature, indicating proximity to the manufacturer’s specified limit. The study suggests further research and development to improve the performance of electrolytic capacitors in SMPS systems under cold conditions, aiming to boost efficiency and reliability.

Calibration of 10 nF capacitance standard from DC quantum Hall resistance using a digital impedance bridge

This paper describes the calibration of a 10 nF capacitance standard traced to the DC quantum Hall resistance primary standard using a multi-purpose digital impedance bridge. The bridge can directly compare the unlike impedances in the fully digital (FD) mode, so the capacitance standard can be calibrated by a direct comparison against the AC resistance standard. The measurement ability of the bridge in the FD mode was evaluated in various angles, and the bridge voltage dependencies were improved by selecting appropriate impedances for the high current arms and also by using an additional injection circuit. Thereby, the measurement accuracy could reach up to 10−7 in relative terms. Based on the bridge evaluation, a 10 nF capacitance standard was calibrated against a 10 kΩ resistance standard, and the measurement value agreed with a reference value in the level of 10−7.

Packaged Flexible Planar Copper Foil Fractional-Order ‘0.61–0.87’ Capacitors: Series/Parallel Combinations

The fabrication of packaged, flexible, and planar fractional-order capacitors (FOCs) using copper foil electrodes and thin films of PVDF polymer nanocomposite dielectric is presented in this paper. An extensive comparison of FOC properties is made by using two separate conductive fillers, i.e., graphene nanosheets (GNS) and reduced graphene oxide (rGO). Similar fractional-order is observed at a particular filler loading in both types of FOCs; however, differences in the pseudocapacitance values and width of the constant phase (CP) zone exists. Fractional order α (alpha) is reported to vary in the range 0.61–0.87 in impedance measurements made on individual samples of rGO/PVDF and GNS/PVDF FOCs and series/parallel connections of two identical-order FOCs. For series/parallel connection of arbitrary-order FOCs, α varies from 0.61 to 0.83. Phase angle variation ranges from − 56.2° to − 79° for standalone pure FOC samples, whereas, for series/parallel connection of identical or arbitrary order FOCs, phase ranges from − 54.94° to − 77.75°. Phase ripple varies between ± 1.1° and ± 4.8°, and a maximum CP zone of 4 decades (1 kHz to 10 MHz) for the fabricated samples is reported. Industrial manufacturing of large-value capacitors demands materials to be flexible to enable rolling of large-area electrodes into a miniature device. FOCs fabricated in this work match the design specifications of commercial standard thin film capacitors and show high-value capacitances as well as flexibility of materials and structure.

Bilateral Comparison of High-Voltage Capacitance and Dielectric Dissipation Factor at 50 Hz

NIM (National Institute of Metrology, China) and NMIA (National Measurement Institute, Australia) carried out a comparison program, which included low-voltage capacitance, the voltage dependence of high-voltage capacitance and the dielectric dissipation factor (DDF) at 50 Hz. The travelling standards included a low-voltage standard capacitor, a dissipation factor standard and a 100 kV compressed-gas capacitor. The capacitance and DDF of the standard capacitor, measured by the two institutes, agreed within 2 μF/F and 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> , respectively, at 50 Hz and 500 V. DDF measurements at nominal values of 0.00000, 0.0001 and 0.001 agreed within 6×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> at 50 Hz and 10 kV. The capacitance change of a 100 kV compressed-gas capacitor measured by the two institutes agreed within 2 μF/F over the voltage range from 10 kV to 100 kV. The success of the program proved comparisons using a re-filled high-voltage compressed gas capacitor and a low-voltage standard capacitor can be conveniently used to validate the complete traceability chain of the measurement of high-voltage capacitance at 50 Hz. The program also proved that DDF measurements with different implementations of traceability chain via capacitance and resistance would agree well within the uncertainties required by industrial measurements and a commercial DDF standard that has undergone international air travel would be sufficiently stable.

Mode Switching Based Parameter Identification for 2TX-1RX Wireless Power Transfer Systems

Parameters within wireless power transfer (WPT) systems could vary for different reasons. On one hand, mutual inductances and load conditions could vary due to different operating points of the WPT system. On the other hand, the values of capacitors within the WPT system could also vary due to aging issues. Identifying those parameters is of great importance to ensure highly efficient, controllable, and reliable operation for WPT systems. However, those parameters are strongly coupled within the system and are quite challenging to be estimated at the same time. This paper proposes a model based method to estimate all the parameters of interest, including mutual inductances, load condition, and all the capacitances, for multi-coil WPT systems with 2 transmitting coils (2TX) and 1 receiving coil (1RX). Specifically, to overcome the challenge of estimating many parameters at the same time, the idea of “mode switching” is applied to greatly improve the redundancy of the parameter identification problem. Auxiliary standard capacitors are introduced into the system to enable the switching of different operating modes. Afterward, a mathematical model is established to describe the physical laws among all the interested parameters in each mode, including the fundamental frequency and harmonic components. Finally, a standard solve procedure is introduced to solve the nonlinear model and calculate the parameters. The method only requires transmitter side measurements, without any information from the receiver side. Experiments conducted on a prototype of a 2TX-1RX LCC-S WPT system verified the effectiveness of the proposed parameter identification method.

Control of Dynamic Performance Through Feedback Converter SSC In Grid Integrated Wind Energy System

A feedback converter-based Static series compensator (FBC-SSC) is a device that can simultaneously compensate for currents and voltages in a distribution network to enhance the Power Quality (PQ) in Grid integrated Energy System (GIWES). PQ is a term that refers to the conjunction of voltage and current stability. Electronically operated and non-linear gadgets with significant applicability in distribution networks and enterprises have become significant aspects due to PQ constraints such as imbalance voltage and frequency, and transients. Improved hysteresis-based FBC-SSC is suggested in this study for optimizing PQ in GIWES. The novelty in this research is improved hysteresis or hybrid PI and PWM-based hysteresis controlled FBC-SSC. In a wind turbine generation system, improved hysteresis based is used to find the gate trigger pulse for SSC. The suggested controller, when combined with FBC-SSC, improves the WES dynamic performance. Simultaneously, the grid network can compensate for current and voltage irregularities in nearby terminals. All converters in the proposed topology share a standard dc-link capacitor. As a result, power can be transmitted from one distributor to another. The proposed topology is modelled in the MATLAB/SIMULINK environment. The effectiveness research is performed using the improved hysteresis controller. Finally, the obtained results are compared to two existing controllers: a Proportional Integral controller and a traditional Pulse Width Modulation (PWM) controller. As a consequence, the performance level can show that the advised technique is effective. When compared to another typical control approach, the suggested system obtains remarkably low THD values of 0.94 percent.

PTB–INRIM comparison of novel digital impedance bridges with graphene impedance quantum standards

This paper describes an onsite comparison of two different digital impedance bridges when performing measurements on a quantum Hall resistance standard with the purpose of realizing the SI unit of capacitance, the farad. In the EMPIR Joint Research Project 18SIB07 GIQS, graphene impedance quantum standards, the Physikalisch-Technische Bundesanstalt (PTB), Germany, developed a Josephson impedance bridge, and the Istituto Nazionale di Ricerca Metrologica (INRIM) and the Politecnico di Torino (POLITO), Italy, developed an electronic digital impedance bridge. The former is based on Josephson waveform generators and the latter on an electronic waveform synthesizer. The INRIM–POLITO impedance bridge was moved to PTB and the two bridges were compared by measuring both temperature-controlled standards and a graphene AC quantized Hall resistance (QHR) standard. The uncertainties for the calibration of 10 nF capacitance standards at 1233 Hz are within 1 × 10−8 for the PTB’s bridge and around 1 × 10−7 for the INRIM–POLITO’s bridge. The comparison mutually validates the two bridges within the combined uncertainty. The result confirms that digital impedance bridges allow the realization of the SI farad from the QHR with uncertainties comparable with the best calibration capabilities of the BIPM and the major National Metrology Institutes.

Primary Realization of Inductance and Capacitance Scales With a Fully Digital Bridge

This paper describes an automated electronic fully-digital bridge for the comparison of four-terminal-pair impedance standards in the audio frequency range. The bridge relative accuracy, which is on the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> , makes it suitable as a reference bridge for the realization of primary scales of inductance and capacitance in metrology institutes and calibration laboratories. The performances of this bridge were validated by comparing the results of the calibrations of inductance and capacitance standards with those obtained from an existing analog reference system based on the three-voltage method. The paper also reports the results of this validation.

Capacitive Readout System for Micro Sensors and Actuators With Automatic Parasitic Cancellation

In this article, a capacitive readout system with automatic parasitic capacitance cancellation function is designed and implemented. The readout system is implemented with discrete components on a board level. The parasitic cancellation is realized by matching a digital programmable capacitor to the parasitic capacitance using a PI controller. The function of the readout system is verified by using standard ceramic capacitors and a MEMS micromirror device. Capacitance measurements up to 35 pF for ceramic capacitors are performed, the maximum error between the measurement results of the circuit and an LCR meter is 0.07 pF. For MEMS micromirror, the circuit cancels the parasitic capacitance of 32.63 pF and realizes a measurement error within 0.06 pF. The proposed system can be used as a proof-of-concept platform demonstrating the feasibility of the generic parasitic cancellation method for MEMS sensors and actuators.

Comparison of four-terminal-pair 1 pF, 10 pF, 100 pF and 1000 pF capacitance standards at frequencies of 10 kHz, 100 kHz, 1 MHz and 10 MHz (APMP.EM-S15)

Main textIn order to calibrate an LCR meter, metrological traceability of capacitance above 10 kHz becomes more and more important. For this reason, NIM (National Institute of Metrology, China)，NPLI (National Physical Laboratory, India) and NIMT (National Institute of Metrology, Thailand) have carried out research on capacitance metrology from 10 kHz to 10 MHz.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Capacitive sensor readout circuit based on sample and hold method

This paper presents a capacitive sensor readout circuit using sample and hold method. The proposed readout circuit is used to convert capacitance from sensor to DC (direct current) voltage output. The basic structure of readout circuit consists of the pulse generator circuit, differentiator circuit, amplifier circuit, monostable I circuit, monostable II circuit, and sample and hold circuit. The proposed technique is based on the change of time constant from differentiator circuit corresponding to the measurement capacitance. The sample and hold circuit is used for sampling output voltage from differentiator circuit. The output voltage of the proposed readout circuit is proportional to measurement capacitance. The standard capacitors with different capacitance are used to test the proposed converter performance. Experimental results show that the proposed readout circuit can convert measurement capacitance to output voltage with satisfied values, good linearity and high sensitivity.

A New Structure of 8-Bit 60 MS/s SAR-ADC Using a Reduced Switching Capacitor-DAC Array

This paper presents an analysis of the Reduced Switching Capacitor Digital-to-Analog Converter (RSC-DAC)-based low power Successive Approximation Register Analog to Digital Converter (SAR-ADC). The proposed structure involves the Low voltage Static D-Latch Comparator (LSD-LC) with pre-amplifier operators in two modes (Normal and Hold), the RSC-DAC switching energy, reduced by 93% contrast to the standard Charge Redistribution Switching Capacitor DAC (CRSC-DAC) method, and the Successive Approximation Register (SAR) control logic. The LSD-LC with pre-amplifier consists of a latch circuit and a pre-amplifier. The pre-amplifier is often used to eliminate the DC offset voltage and kickback noise without substantially weakening the Signal-to-Noise Ratio (SNR) to drive the main circuit while the latch is needed for comparison. The linearity parameters such as Integral Nonlinearity, Differential Nonlinearity and effect of parasitic capacitances of the RSC-DAC are analyzed and improved by the new approach named as Adaptive Random Code Generation (ARCG) Technique. The above overall design is implemented in 250-nm CMOS design of the TANNER-EDA tool, consuming 1.74-mW power at 60[Formula: see text]MS/s. The proposed structure has an INL and a DNL, respectively, of +0.18/[Formula: see text] LSB and +0.11/[Formula: see text]0.05 LSB.

Electrochemical impedance in ac diagnostics of weakly conducting media

Impedance ac diagnostics is regularly used to study the transport phenomena in conducting systems of differrent dimensionalities. A common reason for using ac methods that are more complex than dc methods is the possibility to exclude the influence on the current-voltage (I−V) characteristic of contact phenomena accompanying dc measurements. In some cases (2d electron systems over helium) dc transport measurements are impossible. In weakly doped semiconductors (diluted electrolytes), the situation is less critical, but problems with the ohmic properties of the conducting contacts remain. The analysis of the details of the formalism that determines the reaction of a conducting medium to an external disturbance depends largely on the form of Ohm’s law for a conductor introduced into the impedance circuit. If there is a reason to define this law by the formula j = σΕ, where j, σ, E correspond to local values of current density, conductivity, and transport electric field, the structure of complex resistance Z^F(ω) is considered as a force one. If there is a diffusion component in Ohm’s law then the structure of complex resistance Z^μ(ω) is considered as an electrochemical one. We describe a standard electrolytic capacitor in series RC with a step load in terms of force or complex electrochemical impedance. Comparison with experiment shows the electrochemical structure of the complex resistance.