Residual‐based a posteriori estimators for the potential formulations of electrostatic and time‐harmonic eddy current problems with voltage or current excitation

Electrochemical characterization of high-power lithium ion batteries using triangular voltage and current excitation sources

This paper compares the short-circuit performance of superconducting (SC) generators with three different topologies, i.e. iron-cored stator and rotor, iron-cored stator and air-cored rotor, and air-cored stator and rotor. The analysis is based on three-phase short-circuit fault, and finite element analysis is used for simulation. Following the introduction of specifications of generators, the short-circuit performances of different topologies are analysed and compared, with the field winding excited by voltage and current excitation sources, respectively. It shows that the short-circuit performance can be improved by limiting the field current.

The time-harmonic eddy current problem with either voltage or current intensity excitation is considered. We propose and analyze a new finite element approximation of the problem, based on a weak formulation where the main unknowns are the electric field in the conductor, a scalar magnetic potential in the insulator and, for the voltage excitation problem, the current intensity. The finite element approximation uses edge elements for the electric field and nodal elements for the scalar magnetic potential, and an optimal error estimate is proved. Some numerical results illustrating the performance of the method are also presented.

A Finite Element method that uses a hinged weighting function is applied to 1-D and 2-D eddy current problems. A method of choosing the hinge parameters such that the resulting piecewise linear function approximates an exponential weighting function is developed. A special purpose quadrilateral element that incorporates the hinged weighting function is derived. The hinged elements are used to solve 1-D and 2-D eddy current test problems. Computed results that illustrate the advantages of the hinged F.E.M. are presented.

Artificial boundary conditions for axisymmetric eddy current probe problems

This paper provides a method and a system based on current pulse excitation and frequency spectrum analysis, which can complete battery impedance spectrum test and analysis. By exerting current excitation onto the battery, synchronously measuring current excitation and terminal voltage response, we count the amplitude spectrum and phase spectrum for current excitation and terminal voltage response under different frequencies. Also, we count the battery impedance under different frequencies according to spectrums of I and U, to get the complete spectrogram for the battery impedance. The technology provides a new solution for calculating and predicting the charge state and health state of the storage battery.

The authors consider eddy current diffusion problems in which the electromagnetic field is computed in 2-D but external circuit connections, between the conductors with eddy currents are taken into account. The approach combines conventional circuit analysis techniques with the integro-differential finite element formulation of the transient eddy current problem. Conductors with eddy currents are treated as circuit elements with terminal voltages implicitly defined by the field equations. A numerical example is presented to illustrate the proposed formulation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.

We present a method to model organic light-emitting devices driven by a current source in the context of drift-diffusion models. The method is extended to the case of voltage excitation, and calculations with current and voltage excitation are compared. An advantage over the application of Poisson's equation is that standard numerical solvers can be used for the ordinary differential equations that result from the spatial discretization of the model equations. We employ the model to calculate I- V characteristics and to examine the transient response of an organic light-emitting diode under pulsed current operation. The approach is generalized to the case of an arbitrary number of layers.

Most papers concerning the calculation of 3D eddy current problems are using a combination of a vector potential and a scalar potential to solve the electromagnetic field in the eddy current regions. This paper uses the A/spl I.oarr/-A/spl I.oarr/, T/spl I.oarr/ formulation with both the magnetic vector potential A/spl I.oarr/ and the electric vector potential T/spl I.oarr/ in the eddy current regions. Since nodal vector potentials with continuous normal components have accuracy problems at interfaces of regions with different permeabilities, edge elements can be used for both potentials. The formulation is applied to the calculation of stationary eddy current field problems induced by motion, time-harmonic and transient eddy current field problems.

Electrical impedance spectrum tomography (EIST) has become an important tool for biomedical and electrochemical research. Compared with the existing electrical impedance tomography, EIST can reveal the richer frequency information with higher resolution on the electrical properties analysis of biological materials, including amplitude and phase shift over a continuous frequency range. To achieve these functions, a dedicated hardware system must be developed to meet the requirement of wide frequency range and flat spectral characteristic. In this paper, a wideband chirp signal excitation source was designed to drive bioimpedance tissues. According to mathematical mechanism of a chirp signal, high quality chirp signal was generated with field programmable gate array and direct digital synthesis method. Furthermore, on the basis of single resistance calibration, experiments based on three elements impedance loads were executed to verify the feasibility and performance of the excitation source design. The measured results illustrate that the current excitation source has a qualified driving capability. Sensitive spectral response of amplitude and phase shift can be obtained by means of wideband chirp signal.

Design optimization and reliability assurance of electrical machinery and devices require accurate prediction of the magnetic field distribution in their active region. The finite element method offers a stable numerical solution technique with a high degree of precision. This method is based on formulating the partial differential equations of the magnetic field problem in variational terms and minimizing the associated functional by a set of trial functions. This paper describes the application of finite-element analysis to electric, magnetic and eddy-current field problems in rotating machinery, static apparatus, and devices. Some of the areas surveyed are magnetic fields in synchronous machines, dc generators, transformers, eddy-current problems in conducting media, and electrostatic applications.

The objective of this work is the analysis of a time-harmonic eddy current problem with prescribed currents or voltage drops on the boundary of the conducting domain. We will focus on an ungauged formulation that splits the magnetic field into three terms: a vector potential T, defined in the conducting domain, a scalar potential φ, supported in the whole domain, and a linear combination of source fields, only depending on the geometry. To compute the source field functions we make use of the analytical expression of the Biot-Savart law in the dielectric domain. The most important advantage of this methodology is that it eliminates the need of multivalued scalar potentials. Concerning the discretisation, edge finite elements will be employed for the approximation of both the source field and the vector potential, and standard Lagrange finite elements for the scalar potential. To perform the analysis, we will establish an equivalence between the T,φ-φ formulation of the problem and a slight variation of a magnetic field formulation whose well-possedness has already been proved. This equivalence will also be the key to prove convergence results for the discrete scheme. Finally, we will present some numerical results that corroborate the analytical ones.

This paper presents a novel hybrid excited synchronous generator (HESG) for high-speed and high-power applications. The generator features a surface mounted permanent magnet (PM) rotor wrapped by a carbon fiber bandage, and excitation windings fixed under the tangential magnetized magnets to control air-gap flux density. Based on the theory of elastic mechanics, the stress and deformation in the carbon fiber bandage is calculated analytically, and the relationship between the air gap length and magnet thickness is obtained. To optimize the hybrid ratio between PM and current excitation sources, parametric model is built and computed by 2D finite-element method.

We give a systematic presentation of voltage or current intensity excitation for time-harmonic eddy-current problems. The key point of our approach resides in a suitable power law that permits us to understand the role of voltage excitation. We also shed light on the influence of the boundary conditions on the proposed formulations.