Power battery impedance spectrum test technology based on current pulse excitation and frequency spectrum analysis

Pulsed eddy current imaging and frequency spectrum analysis for hidden defect nondestructive testing and evaluation

This paper presents an analytical method for electromagnetic acoustic transducers (EMATs) under voltage excitation and considers the non-uniform distribution of the biased magnetic field. A complete model of EMATs including the non-uniform biased magnetic field, a pulsed eddy current field and the acoustic field is built up. The pulsed voltage excitation is transformed to the frequency domain by fast Fourier transformation (FFT). In terms of the time harmonic field equations of the EMAT system, the impedances of the coils under different frequencies are calculated according to the circuit-field coupling method and Poynting's theorem. Then the currents under different frequencies are calculated according to Ohm's law and the pulsed current excitation is obtained by inverse fast Fourier transformation (IFFT). Lastly, the sequentially coupled finite element method (FEM) is used to calculate the Lorentz force in the EMATs under the current excitation. An actual EMAT with a two-layer two-bundle printed circuit board (PCB) coil, a rectangular permanent magnet and an aluminium specimen is analysed. The coil impedances and the pulsed current are calculated and compared with the experimental results. Their agreement verified the validity of the proposed method. Furthermore, the influences of lift-off distances and the non-uniform static magnetic field on the Lorentz force under pulsed voltage excitation are studied.

Power simulation of lithium ion battery through battery model is of great significance for dynamic response simulation, heat generation calculation and charge-discharge strategy development. The accuracy and applicability of the model become crucial. In order to demonstrate the battery transient characteristics more effectively, a novel identification method for parameters of the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> order RC equivalent circuit model was proposed. Based on the derived evolution law of battery transient characteristics under the continuous pulse excitation, four feature points are extracted for parameter identification in each cycle. The proposed method reduced the time cost of identification from 11796.88s to 0.06s while ensuring that the error of voltage doesn't exceed 2.2mV. In order to verify the power profiles applicability of the proposed method, applicability analysis of power profile for different identification methods was carried out including the methods using different amount of data (4N points, 200 points, 6000 points) under unidirectional current pulse excitation (UCPE), bidirectional current pulse excitation (BCPE) and unidirectional voltage pulse excitation (UVPE). It was illustrated that the identification process using data of multiple cycles could significantly reduce errors, including maximum error and average error. What's more, the proposed method under UCPE had the lowest maximum error of 0.420% in voltage simulation and -0.421% in the current simulation of power profiles. Compared with the conventional method (using 200 points of single pulse data for parameter identification), the proposed method can reduce the average voltage error and the maximum error by 62.5% and 11.8% respectively under the DST power profile.

The aim of this work is to analyze different formulations of the voltage excitation problem and the current intensity excitation problem for the time-harmonic eddy-current approximation of Maxwell equations in the case of a conductor with electric ports. Two formulations based on the introduction of a vector magnetic potential and their finite element approximation are analyzed.

Gas Tungsten Arc Welding (GTAW) involves several process parameters. In Pulsed Current GTAW frequency of pulse and pulse to time ratio differentiates the characteristics of weld pool geometry of from GTAW. In the present work a simple heat transfer model for Pulsed Current GTA welding was developed and the weld pool dimensions were experimentally verified with AISI 1020 steel. Relationship between speed and pulsed current frequency on weld pool dimension was studied. Weld pool dimension of pulsed and non-pulsed GTAW is studied.

Three-dimensional (3D) integration sets improved requirements on the structure and performance of the Ni deposits. Pulse reverse current (PRC) electroplating is regarded as a promising technique to obtain Ni plating fulfilling such requirements. This work investigated the influence of two PRC parameters, average current density and pulse frequency, on surface morphology and grain size of the Ni deposits. Ni deposits were prepared by first direct current (DC) pre-plating and then PRC electroplating process of given average current density and pulse frequency. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were employed to characterize the deposits. It was found that the surface morphology and grain size of the Ni deposits were significantly influenced by average current density and pulse frequency. Such results are instructive in the electroplating obtainment of Ni for packaging applications.

The application of hybrid excited synchronous generator as a part of autonomous wind turbine is studied in a case of load and wind speed changes. The control system of autonomous wind turbine ensures maximum wind turbine power output at any given wind speed. Maximum power achieved by excitation current control in additional field winding. The excitation current and power control of generators is developed based on minimization of local functionals of instantaneous values of first order derivative of electromagnetic energy. It provides robustness to parametric and coordinate disturbances and high quality of control. On the example of an experimental sample of a synchronous generator with hybrid excitation the studies of maximum output power control of autonomous wind turbine were carried out. The study is carried out in a case of wind speed variation from 3 to 8 m/s and load increasing by 50%. The graphs of output power of wind turbine, speed and torque of generator, excitation and armature voltage sand currents are given.

Generator or alternator is a device that has a function to convert or transform mechanic energy to electricity. Electricity conversion need process with giving strengthening with excitation current to coil magnetic field that placed on sync generator. Excitation current that flows on magnetic field coil will cause magnetic flux. Generator sync on PLTU unit 3 and 4 PJB UP Gresik use excitation system with excitation static type, this type of excitation it uses carbon brush as a media to conduct excitation current, this excitation system use the output of sync generator. In reality this excitation current which exist on PLTU unit 3 and 4 have to should always be taken care so the system can operate normally and commonly the fault that happened is under excitation and over excitation so it can be prevent. Step taken to avoid damaging the generator sync that caused by excitation current, steps that have to be taken are understanding the characteristic of system excitation setting, anchor current, voltage generator, and loading. The value of loading is very affecting the value of excitation current that injected to generator, the purpose of this process of excitation current injection is to maintain the stability from sync generator voltage so that the condition is staying on its normal condition.

The dependence of magnetic Barkhausen emissions (MBE) upon both field excitation and detection frequencies and excitation wave form was studied in order to investigate two of several crucial factors which affect the emissions. Sinusoidal, triangular, and square wave forms were used to generate the MBE and the pulse height spectra, frequency spectra, and pulse wave forms of these signals were analyzed. The frequency spectra of sinusoidal and triangular alternating field excitations showed similar behavior but the spectrum under square wave excitation was different due to the existence of high frequency components during square wave switching. As yet, no common standard has been agreed upon for parameterization and representation of Barkhausen signals. It appears from this work that field excitation wave form and frequency should define the inputs, while detection frequency range, pulse height spectrum, frequency spectrum, and emitted pulse wave form analysis should be used to quantify the output.

A Magneto-Optic (MO) system is being utilized in aerospace industry for the detection of surface defects. To extend the capability of the instrument to detect and quantify sub-surface defect, we present a new Magneto-Optic (MO)/Pulsed Eddy Current (PEC) imaging system which, supported by laser, is being used for testing fine defects beneath precision surface of mental materials. The technique is based on the combination of pulsed eddy current excitation and magneto-optic sensing and imaging. In the experimental set-up, the induction of eddy currents is conventionally performed by pulsed current excitation coil over the object surface. The magnetic field induced by the pulsed eddy currents is detected by using Faraday effect. For this target, a laser beam passes through a special crystal, Faraday rotation glass (FRG), which has its easy axis of magnetization in the direction of normal magnetic fields and memory effect, integrated in the excitation coil. The polarization direction of laser beam is rotated in crystal depending on local magnetic field. The area distribution of rotation angle caused by fine defects beneath precision surface is transformed into "light" or "dark" picture using an optical set-up, which consists of a conventional microscope, a lighting, a polarimeter, and a CCD sensor. In the paper, the basic principle, configuration of the test equipment and image processing are described, and an original experimental results of fine artificial defects beneath precision surface of mental materials is presented.

Effects of current pulse frequency and duty ratio [off-time/(on-time + off-time)] on thermoelectric properties of bismuth telluride (Bi2Te3) thin films were investigated. The crystal structure of the Bi2Te3 thin films was strongly affected by the duty ratio rather than the current pulse frequency. In particular, the Bi2Te3 thin films were highly oriented along (1 1 0) direction with smooth surface at the high current pulse frequency (5000 Hz) and the high duty ratio (80%). Overall, the electrical conductivities of the Bi2Te3 thin films with current pulse frequency of 5000 Hz were larger than that the thin films with 1000 Hz, whereas the Seebeck coefficients were mostly the same between the both frequencies. As a result, the highest power factor (1.1 μW/(cm·K2)) was observed at the Bi2Te3 thin films with a current pulse frequency of 5000 Hz and a duty ratio of 60%.

Electrochemical impedance measurement systems use the Bode analysis technique to characterize the impedance of an electrochemical process. It is a well established and proven technique. The battery being evaluated is excited with a current that is single frequency and its response is measured. The process is repeated over a range of frequencies of interest until the spectrum of the impedance is obtained. The method is effective but time consuming, as the process is serial. A parallel approach using band width limited noise as an excitation current can obtain the same information in less time. The system response to the noise is processed via correlation and fast Fourier transform (FFT) algorithms and many such responses are averaged. The result is the spectrum of response over the desired frequency range. The averaging of many responses also makes this process somewhat serial. Another technique assembles the current noise waveform from a sum of sinusoids each at a different frequency. The system response as a time record is acquired and processed with the FFT algorithm. To reduce noise multiple time records of waveforms are processed and their resultant spectra averaged. This process is also serial. There is interest in real time acquisition of battery impedance for control and diagnostics over a limited frequency range. To support this need a true parallel approach is proposed that uses a single acquired time record of the battery response with duration compatible to a real time control process. The time record duration is the battery impedance sample period. If that sample period can be as short as 10's of seconds then, many control system algorithms can use battery impedance as a sensed variable.

Parametric analysis is used to predict whether induction or current channeling dominates the current excitation in a conductive body in the earth. Knowing that one mode dominates the current response permits the use of relatively simple models that account for only a single mode of excitation in place of more complicated general ones that account for both modes of the current response. This is useful both in forward modeling and in inversion. In interpretation, predicting the current excitation is useful for verifying that the assumed mode of excitation is consistent with the interpreted body. Prediction is done with a set of “current excitation ratios” that we demonstrate for a thin conductive plate in a conductive half‐space. To derive the excitation ratios, parametric theory is used to estimate the strength of the inductive and galvanic modes of the current response of the plate. The ratios then follow by dividing the inductive estimate into the galvanic one. When this ratio is less than one, induction will dominate the current response. When it is greater than one, current channeling will dominate. Current excitation ratios are simple to calculate, and consist of two components. One component is a product of model parameters such as conductivity, dimension, and permeability, and can be calculated by hand. The second component consists of what we term the “local impedance” of the source field at the conductor. This component can be calculated with a simple half‐space or layered earth electromagnetic modeling algorithm and then contoured for later reference. The predictive capability of the current excitation ratios is tested by calculating the current response on a vertical plate in a half‐space with a full electromagnetic scattering solution. We find the correspondence between the two to be very good, and that it is possible to successfully predict the dominant mode of the current response through parametric theory where assumptions used in the parametric analysis are valid.

This study investigated the effects of pulsed current frequency and shielding gas composition on the weld metal geometry and nitrogen content. Austenitic stainless-steel sheets were welded by gas tungsten arc welding using 0, 0.5, 1, 2, 5, and 10 vol.% of nitrogen gas in argon shielding gas and pulse frequencies of 40, 80, 120, 160, and 200 Hz. Weld sections were recorded using a stereomicroscope. Weld depth and cross-section of the weld metal were measured by ImageJ® software and their changes were recorded. Nitrogen analysis tests were performed on the weld metal and, the results were analyzed. Investigations revealed that by increasing the nitrogen content of the shielding gas up to 10 vol.%, the nitrogen content of the weld metal almost doubles at the maximum nitrogen level. This increase was more considerable at higher current frequencies. Also, by increasing the pulsed current frequency, the weld pool and the weld metal depth-to-width ratio increased to 37 % and 44 %, respectively, at the maximum level of shielding gas nitrogen. In addition, at the frequency of 200 Hz, increasing nitrogen led to an 86 % and 72 % increase in the weld pool and the weld aspect ratio, respectively.

Effect of duty cycle and frequency of pulse current on bidirectional electro-migration rehabilitation