Error In Impedance Measurement Research Articles

Parameter identification of PLL for grid‐connected inverter based on parameter sensitivity analysis

AbstractUnder the condition of weak grid, the phase‐locked loop (PLL) is one of the main reasons for the sub‐synchronous oscillation of the grid‐connected inverter. Therefore, it is necessary to identify the PLL parameters of the grid‐connected inverter for the analysis of the inverter operating performance. This paper uses the sequence impedance model and measured impedance data of grid‐connected inverter to construct the identification function for parameter identification of PLL, and the function is calculated by particle swarm optimization algorithm to overcome the nonlinear problem of sequence impedance model. In addition, the identification frequency band is selected based on PLL parameter sensitivity to improve the parameter identification accuracy under the same impedance measurement error. At different frequencies, the positive correlation between the sensitivity of the PLL parameters and the identification accuracy is proven to determine the definite frequency band for PLL parameter identification of grid‐connected inverter. Finally, the feasibility and effectiveness of the above research are verified by simulation and semi‐physical experiments.

Advanced Electrochemical Analysis of All-Solid-State Battery Electrodes Using Novel Potential-Controllable Symmetric Cell

In this study, we propose a novel potential-controllable symmetric cell (PCSC) for the reliable analysis of the electrode/electrolyte interface and bulk characteristics of the active material in an all-solid-state battery (ASSB). Unlike a conventional symmetric cell, which requires the disassembly and reassembly of two unit cells with the same voltage to analyze the reactions at specific potentials, our PCSC self-adjusts the potential by lithiating/delithiating the electrodes without requiring dismantling. Specifically, a mesh-like temporary counter electrode was inserted into the center of the solid electrolyte inside the cell to allow voltage regulation of both electrodes without interfering with ion transport through the electrolyte. This is particularly useful for interpreting the reactions in ASSB, which are practically impossible to reassemble after dismantling. In addition, it eliminates the impedance measurement errors associated with the distortion of the internal structure induced by the reference electrode in a three-electrode cell, which is more detrimental to an ASSB than a conventional liquid electrolyte-based battery. As a practical example, we comparatively analyzed the characteristics of a LiNbO3-coated LiNi0.8Co0.1Mn0.1O3 (c-NCM811) cathode using conventional test cells (two- or three-electrode all-solid-state half cells) and an all-solid-state PCSC. The PCSC exhibited a clearer interfacial signal for c-NCM811 than that obtained from a conventional two-electrode half-cell. Furthermore, compared to the three-electrode all-solid-state half-cell, the PCSC provided a relatively well-resolved interfacial reaction signal. The bulk properties of c-NCM811 proved that our PCSC provided very reliable and consistent Li diffusion coefficients using various methods, including the constant phase element-restricted diffusion model, galvanostatic intermittent titration technique, and the Warburg–blocking transition-frequency estimation method.

Improving Small-Signal Stability of Grid-Connected Inverter Under Weak Grid by Decoupling Phase-Lock Loop and Grid Impedance

The wide bandwidth of phase-locked loop (PLL) will increase the negative real part of the output impedance of the grid-connected inverter (GCI), thus destroying the stability of the weak grids. This article proposes a novel method to improve the system stability through decoupling the PLL and grid impedance. Initially, the coupling relationship between PLL and grid impedance is revealed. It can explain why the choice of PLL bandwidth and the grid impedance magnitude is limited. Then, the decoupling method is proposed where the primary control structure of GCI does not need to change and uses the structured voltage, the product of PCC voltage and grid admittance, as the improved input of PLL. The proposed method can achieve the full-frequency passive of the output impedance of GCI even if the PLL has high bandwidth and the impedance measurement error is up to 60%, which means the adverse stability effect of PLL on the system is eliminated. The theoretical analysis is verified by simulations and experiments.

Guidelines to correctly measure the lithium ion conductivity of oxide ceramic electrolytes based on a harmonized testing procedure

Ionic conductivities of Li-ion conducting ceramic electrolytes, mostly evaluated by means of impedance spectroscopy, are a key parameter decisive for their application. Nevertheless, significant deviations in the ionic conductivity of nominally identical samples are reported in literature, which are attributed to material and sample preparation as well as measurement related differences. The goal of this study is a detailed assessment of impedance measurement deviations of 10 identically prepared samples of each Li6.45La3Zr1.6Ta0.4Al0.05O12 (LLZO:Ta:Al) and Li1.3Al0.3Ti1.7(PO4)3 (LATP), respectively. By introducing a harmonized testing procedure for impedance measurement and data analysis, deviations among the participating labs were reduced to differences <1.8% for LLZO and <3.1% for LATP. A complete assessment of instrumentation (fitting, temperature and impedance measurement errors) and sample geometry related errors revealed a high measurement precision with a total error <1.1%. Further on a decreasing ionic conductivity was observed for both materials during the study. Indications for testing and storage induced aging mechanisms were obtained by additional measurements.

Wrist-wearable bioelectrical impedance analyzer with miniature electrodes for daily obesity management

Bioelectrical impedance analysis (BIA) is used to analyze human body composition by applying a small alternating current through the body and measuring the impedance. The smaller the electrode of a BIA device, the larger the impedance measurement error due to the contact resistance between the electrode and human skin. Therefore, most commercial BIA devices utilize electrodes that are large enough (i.e., 4 × 1400 mm2) to counteract the contact resistance effect. We propose a novel method of compensating for contact resistance by performing 4-point and 2-point measurements alternately such that body impedance can be accurately estimated even with considerably smaller electrodes (outer electrodes: 68 mm2; inner electrodes: 128 mm2). Additionally, we report the use of a wrist-wearable BIA device with single-finger contact measurement and clinical test results from 203 participants at Seoul St. Mary’s Hospital. The correlation coefficient and standard error of estimate of percentage body fat were 0.899 and 3.76%, respectively, in comparison with dual-energy X-ray absorptiometry. This result exceeds the performance level of the commercial upper-body portable body fat analyzer (Omron HBF-306). With a measurement time of 7 s, this sensor technology is expected to provide a new possibility of a wearable bioelectrical impedance analyzer, toward obesity management.

Parametric sensitivity analysis of SEL-421 distance relay algorithms used in compensated line

This paper presents the use of Global Sensitivity Analysis (GSA) methods to analyze the sensitivity level of the performance of the impedance measurement algorithm of SEL-421 distance relay protection when used to perform transmission line protection with compensation circuit. This GSA technique was developed to see the dominance effect of system uncertainty (or factors). Two techniques that might be used for sensitivity analysis using GSA are Quasi-Monte Carlo (QMC) and data sampling with Sobol technique. Experimental is done with DIgSILENT software to do modeling of the power system, simulation, and calculation of impedance and algorithm error. The testing is carried out automatically with the help of the developed algorithm using DPL (DIgSILENT Programming Language). SIMLAB software, in this case, (with Sobol technique) is applied to generate some non-linear factor data and analyze the output of variations in impedance measurement errors.

Error compensation in distance relays caused by wind power plants in the power grid

This article presents the Prony method as a filtering technique for distance relays. First, the effect of non-filtered frequency components generated by wind power plants in distance relays is evaluated in a simplified model of a doubly fed induction generator, resulting in an error of apparent impedance measurement. Then, the effects of non-filtered frequency components for typical distance relay are presented. The error in apparent impedance measurement is evaluated in reach and operation time of the relay; a distorted characteristic of the mho distance relay is shown in the impedance plane. Finally, Prony method as a filtering technique is implemented as a solution of the apparent impedance measurement error, and the simulated case and a real fault event are evaluated to validate the proposed distance relay algorithm. Thus the asynchronous frequency components of voltage and current signals are identified and filtered, as a result the performance of the distance relay is enhanced.

Design of a Bioelectrical Impedance Spectrometer Based on AD5933

This paper designed a bioelectrical impedance spectroscopy (BIS) measurement system based on the integrated impedance converter AD5933. The working principle of the AD5933 was briefly introduced, and a bipolar BIS measurement device was designed. The AD5933 can be controlled by MCU STC89LE516AD through an I2C bus. The software of the BIS device was written in C51 language and provides a friendly human-machine interface. Preliminary experiment showed that the impedance measurement error at different frequencies is less than 3% and found that the measurement accuracy is relatively high for larger resistor.

Study on a New Setting Method of Distance Relay with Superconducting Fault Current Limiter Adapt in the Grid

Considerable attention is given towards developing Superconducting fault current limiter (SFCL) due to increasing short circuit levels in transmission lines, which itself imposes further changes on the measured impendence at the relaying point and causes significant impact on the lines’ relay protection, especially on the distance protection as the single-phase grounding fault occurs. In this paper, resistive superconducting fault current limiter connected to the grid is studied as the model to analysis how SFCL affects the grounded short-circuit impedance relay’s setting, then an new setting method of distance protection for the SFCL-equipped line is proposed. Finally, a power system model is built to analysis the theory by PSCAD / EMTDC simulation software. The results show that in the condition of using the impedance relays’ new setting method, impedance measurement error is greatly reduced, SFCL and line distance protection can work in coordination with each other properly.

Impedance Spectroscopy of Dye-Sensitized Solar Cells: Analysis of Measurement and Fitting Errors

Errors in impedance measurements made on dye-sensitized solar cells (DSCs) and in subsequent model-based parameter extraction have been analyzed. The variance in the impedance was determined from replicate measurements using a “measurement model” approach. Measurement models were also used to identify corrupt data that were inconsistent with the Kramers-Kronig relations, providing justification for their rejection prior to further analysis. A common equivalent circuit model containing a transmission line was fitted to the refined data, which was weighted by the experimentally determined variance. For comparison, fits were also performed with the common “modulus” weighting strategy. Parameter confidence intervals were constructed from approximate standard errors and also from Monte-Carlo simulations based on the measured variance, which are presumably more accurate. Both weighting strategies yielded practically identical results for the main transmission line parameters, validating use of modulus weighting for routine work on DSCs. However, spectra could not be fitted to within the noise level, indicating that the model may need to be improved. Monte-Carlo confidence intervals were in all cases 10-20% tighter than those calculated from parameter standard errors for variance weighted fits and 3–15 times tighter than those for modulus weighted fits, implying the latter can be viewed as being pessimistic.

Interface circuit for impedance sensors using two specialized single-chip microsystems

The paper presents an interface circuit designed for the measurement of impedance parameters of sensors or measurement cells installed on technical objects. The interface circuit allows measurement of the modulus and argument of impedance in the range of 10 Ω ≤ | Z x| ≤ 10 GΩ at a measurement frequency in the range of 0.01 Hz to 100 kHz. The new solution based on two specialized SoC AD5933 microsystems has been used. This has allowed to obtain miniaturization, low power consumption and low-cost of the circuit of the impedance interface. During tests of the realized prototype using the reference object, the object impedance measurement errors have been determined and they do not exceed ±1.6% (for relative error of impedance modulus) and ±0.6° (for absolute error of impedance argument). The obtained accuracy is fully acceptable in case of impedance measurement of anticorrosion coating in the field. The comparison measurements performed with the aid of Solartron set of instruments showed that the impedance measurement accuracy of the proposed module is comparable to laboratory set of instruments. The important advantage of the used solution based on AD5933 microsystems is lowering the power consumption down to ca. 0.7 W, which makes possible powering the measurement module from a PC using +5 V from the USB. It is a very profitable feature for a module designed to work directly in the field.

Comparative Estimation of Impedance Measurement Errors

Comparing impedance measurement errors in various coordinate systems is considered. An estimator may be based on the area in the complex plane within which the coordinates are undefined on account of the errors.

High-frequency measuring impedance-to-voltage converter

An instrumental impedance-voltage converter operating in the 0.1–10 MHz frequency band is described. The impedance measurement error does not exceed 3%.

Problems involved in temperature measurements using EIT

In cancer therapy, hyperthermic treatment by microwaves requires a non-invasive and reliable method for measuring the temperature distribution inside the body. EIT seems to be able to evaluate the temperature-dependent tissue impedance for delivering the temperature profile in a cross-section of the body. Assuming a temperature coefficient of the resistivity of an electrolyte of about -2% degrees C-1 and temperature measurement to an accuracy of 0.5 degrees C, the error in impedance measurement must be lower than 1%. Irrespective of the accuracy of the tomographic measuring system itself, a problem arises from the fact that the fluid content in the tissue as well as the fluid distribution between the extracellular and the intracellular compartment change with temperature. Measurements of the impedance spectra of skeletal muscle and tumours of rats during hyperthermic treatment deliver very different temperature coefficients of the resistivity from -1.3% degrees C-1 to -3% degrees C-1, thus questioning the feasibility of the EIT as a temperature measuring method. However, changes in the tissue caused by hyperthermia (e.g., fluid shifts, development of oedema and membrane disintegration) can be detected.

Measurements of the acoustic input impedance of cat ears: 10 Hz to 20 kHz

The acoustic input impedence of the ear is a useful measure of the behavior of the middle ear and of its effect on the acoustics of the external ear. A high-impedance acoustic source with an integral microphone was designed for acoustic-impedance measurements. The source's Norton equivalent circuit was determined from measurements of the sound pressure it generated in known acoustic loads. Tests on simple acoustic configurations show errors in impedance measurements of less than 10% in magnitude and 7 degrees in angle over a frequency range from 10 Hz to 10 kHz with increasing errors at higher frequencies. Measurements at the tympanic membrane (TM) on five cat ears with widely opened middle-ear cavities show an impedance that is compliance-like below 0.3 kHz and approximately resistive above 2 kHz. With the cavities intact the impedance magnitude is somewhat larger for low frequencies, has a sharp maximum near 4 kHz, and at the highest frequencies is little affected by the state of the cavities. Impedance magnitude varies among ears by a factor of 3. The pressure reflection-coefficient that is determined from the impedance is frequency dependent with magnitude between 0.2 and 1. To characterize the motion transformation of the TM we calculate the ratio of tympanic-membrane volume velocity to the velocity of the mallear umbo, called here the kinematic area ATK. This complex quantity is constant with an angle of zero for frequencies below 0.6 kHz, but at higher frequencies both magnitude and angle of ATK vary with frequency.

Impedance measurement errors due to non-linearities—I. Low frequency impedance measurements

The effects of electrochemical systems non-linearities on impedance measurements with a Frequency Response Analyser have been investigated in low frequency domain from both a theoretical and experimental viewpoint. A theoretical expression for the polarization resistance measurement error has been found for “non-blocking” electrodes and the measurement validity conditions have been examined. The theoretical approach has been applied to redox reactions and to an adsorbed phase reaction which is a dissolution-passivation process of a metal. The theoretical results were verified with impedance measurements on a platinum rotating disk electrode in a Fe(CN) 3- 6/Fe(CN) 4- 6 redox solution.

Faradaic impedance measurements of small magnitudes encountered in high capacity electrical storage cells

Gross errors in impedance measurements of high capacity electrical storage cells can be observed when using a commercial Frequency Response Analyser (FRA) coupled with an electrochemical interface. The magnitudes of these errors are discussed and an appropriate automatic calibration procedure is described which enables the correct impedance to be recorded at any frequency.

Comments on "Error in Impedance Measurement When the Signal is Introduced Across the Slotted-Line Probe" [Letters

In the above short paper,l an attempt was made to calculate the errors in VSWR and phase caused by detector mismatch in a backwards connected (power into the probe) slotted line. The short paper is wrong. There will be no first-order errors as predicted theoretically in the referenced short paper. The errors encountered in measuring nonlinear devices (diodes) are more complex than those encountered in measuring linear devices. It is very important that the harmonics generated by tbe diode being measured be absorbpd in a matched load and kept out of the detector (especially for high-VSWR diodes). A low-pass filter is commonly used in front of the detector, but (unless it is padded) this filter reflects the harmonic power back into the diode. When the diode being measured does not see a match at the harmonic frequencies, then the harmonic mismatch will interact with the diode to make more efficient or less efficient the conversion to harmonics, depending on the phase relationship between diode and harmonic mismatch. The variable conversion to harmonics will change the impedance of the diode being measured (at the fundamental frequency) as the phase between diode and harmonic mismatch (unpadded low-pass filter) is varied. Therefore, when using a backwards-connected slotted line, it is important to have in front of the detector a low-pass filter that is padded or otherwise matched at the harmonic frequencies as seen from the diode. It is not important for the detector to be matched at the fundamental frequency in a backwards-connected slotted line, as proven in the following discussion.

Error in Impedance Measurement When the Signal Is Introduced Across the Slotted-Line Probe (Short Papers)

For some special applications impedance measurements have to be made where the test level reaching the unknown must be kept very low. In such cases, using slotted-line techniques, the detector and generator are reversed in the test setup, and the test signal is introduced across the probe of the slotted line which is terminated on one side with the load, and on the other with the detector. This short paper briefly describes this familiar method and then discusses the error calculation in the measurement of VSWR and phase when the detector is not perfectly matched.

Distance-protection performance under conditions of single-circuit working in double-circuit transmission lines

When double-circuit transmission lines are operated with one of the circuits isolated and earthed at both ends, relaying conditions can arise that influence the choice of the forward-reach settings of distance protection. Earth-fault conditions during single-circuit working in this way give rise to apparent-impedance values presented to the protection that are generally less, and to errors in impedance measurements that are correspondingly greater, than for the same fault conditions during normal operation, when both circuits are in service together. The paper reports computer studies which seek to compare the discriminative performance of distance protection under earth-fault conditions during double-circuit and single-circuit operation and which, in particular, provide an account of the relaying conditions likely to be encountered in single-circuit operation. Apparent impedance values and associated relaying errors are summarised in tabular form for fault and prefault conditions relevant to a typical 400 kV interconnection, on the basis of which an assessment of the discriminative performance of distance protection in single-circuit working is made.