Topic
Electrical impedance
About: Electrical impedance is a research topic. Over the lifetime, 36015 publications have been published within this topic receiving 371891 citations. The topic is also known as: electrical impedance & complex impedance.
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TL;DR: In this article, a procedure is outlined to transform the measured half-cell impedance to the shape of the equivalent impedance on a microscopically smooth planar electrode, which can be used to obtain a measure of interfacial roughness from the experimental data.
130 citations
TL;DR: A hemispherical dielectric resonator (DR) antenna using aperture coupling for excitation is studied both theoretically and experimentally in this article, where the reciprocity method is used to formulate the problem.
Abstract: A hemispherical dielectric resonator (DR) antenna using aperture coupling for excitation is studied both theoretically and experimentally. The reciprocity method is used to formulate the problem. The exact magnetic field Green's function due to the equivalent magnetic current in the slot is derived rigorously, and it is presented in a form which can be evaluated very efficiently. Moment method is used to solve the magnetic current from which the input impedance of the antenna configuration is obtained. The equivalent radius of the slot is used so that simple formulae developed for the cylindrical dipole can be applied directly. The effects of the slot's length, the slot's position, and the slot's width on the broadside TE/sub 111/ mode input impedance are studied, and reasonable agreement between theory and experiment is obtained. >
129 citations
TL;DR: In this article, a new control scheme for parallel-connected inverters taking into account the effect of line impedance is presented, which is based on instantaneous average current-sharing control that requires interconnections among inverters for information sharing.
Abstract: A new control scheme for parallel-connected inverters taking into account the effect of line impedance is presented. The system presented here consists of two single-phase inverters connected in parallel. The control technique is based on instantaneous average current-sharing control that requires interconnections among inverters for information sharing. A generalized model of a single-phase parallel-connected inverter system is derived. The model incorporates the detail of the control loops that use a proportional-resonant controller, but not the switching action. The voltage- and current-controller design and parameters selection process are discussed. Adaptive gain scheduling is introduced to the controller to improve the current and power sharing for a condition, where the line impedance is different among the inverters. The simulation results show that the adaptive gain-scheduling approaches introduced improve the performance of conventional controller in terms of current and power sharing between inverters under difference line impedance condition. The experiments validate the proposed system performance.
129 citations
TL;DR: In this article, a review of theoretical methods to compute lightning induced currents and voltages on buried cables is presented, and a comparison of several approximations of the ground impedance is presented.
Abstract: In this paper, we present a review of theoretical methods to compute lightning induced currents and voltages on buried cables. The evaluation of such induced disturbances requires the calculation of the electric field produced by lightning along the cable path. We show that the Cooray's simplified formula is capable of predicting accurately the horizontal electric field penetrating the ground, at distances as close as 100 m. Regarding the parameters of the buried cable, a comparison of several approximations of the ground impedance is presented. We show that the Pollaczek expression corresponds to the Sunde general expression, when the displacement current is neglected. The analysis shows also that all the proposed approximations provide very similar results for the considered range of frequencies (up to 30 MHz). Most of the approximate formulas neglect the contribution of the displacement current and, therefore, predict values for the ground impedance which tend to infinity at higher frequencies. This corresponds in the time domain to a singularity of the ground transient resistance at t=0. By analogy to the Sunde approximation for the ground impedance of overhead lines, we propose a logarithmic approximation for the ground impedance of a buried cable. In addition, unlike most of the considered approximations, the proposed formula has an asymptotic behavior at high frequencies; therefore, the corresponding transient ground resistance in the time domain has no singularity at t=0. It is also demonstrated that within the frequency range of interest, the wire impedance can be neglected, due to its small contribution to the overall longitudinal impedance of the line. The ground admittance, however, can play an important role at high frequencies (1 MHz or so) especially in the case of poor ground conductivity. The ground admittance needs to be taken into account in the calculation of lightning induced currents and voltages on buried cables. This is in contrast with the case of overhead lines in which its contribution is generally negligible, even in the MHz range. We also investigate the time-domain representation of field-to-transmission line coupling equations. The coupling model includes the effect of ground admittance which appears in terms of an additional convolution integral. An analytical expression for the ground transient resistance in the time domain is also proposed which is shown to be sufficiently accurate and nonsingular. Finally, we present a time domain solution of field-to-buried cable coupling equations using the point-centered finite difference time domain (FDTD) method, and a frequency domain solution using Green's functions. In our companion paper (Part II), we compare both solutions to experimental waveforms obtained using triggered lightning.
128 citations
TL;DR: In this article, the use of electrochemical impedance spectroscopy and current-interruption techniques with the scope of determining mass-transport limitations in PEFC gas-diffusion electrodes is investigated.
Abstract: The use of electrochemical impedance spectroscopy and current-interruption techniques with the scope of determining mass-transport limitations in PEFC gas-diffusion electrodes is investigated The porous electrode is assumed to be composed of spherical agglomerates consisting of a homogeneous mixture of the electrolyte and the electronic phase The model is applied to the O 2 reduction reaction in the cathode and includes Tafel kinetics for the O 2 reduction, Ohm's law for proton migration, Fick's law for O 2 diffusion, and capacitive current due to the contribution of the double layer A novel impedance is defined, enabling the results to be presented in a simpler manner than with the usual one It is shown how these transient techniques can be employed to qualitatively separate diffusion from migration effects The parameter groups that can be quantitatively determined from the processing of experimental data are presented The effect of O 2 pressure and electrode thickness on the predicted electrode response is also investigated
128 citations