Guido Ala

A simulation model for electromagnetic transients in lightning protection systems

This paper deals with the evaluation of electromagnetic transients in a lightning protection system (LPS). A field approach is used, based on the numerical solution of a modified version of the thin-wire electric field integral equation in the frequency domain. Time profiles of interesting electromagnetic quantities are computed by using a discrete fast Fourier transform algorithm. The model takes into account coupling effects among aerial parts and ground electrodes in order to correctly estimate the quantities which can determine electromagnetic hazard inside the LPS; transient touch and step voltages can be easily evaluated also taking into account the human body presence on the soil surface. To this purpose, a crucial point is the accurate evaluation of the current distribution among the earthed branches of the LPS and this needs to correctly consider mutual electromagnetic interference among the aerial parts and the earth-termination system of the same LPS. A suitable approach to consider the lossy soil is employed. Validation of the proposed model is performed by comparing the results with those measured and computed available in technical literature. Simulation examples related to realistic LPS structures are presented and discussed to show the flexibility and the accuracy of the model in the range of practical applications inside the volume to be protected.

An advanced numerical model in solving thin-wire integral equations by using semi-orthogonal compactly supported spline wavelets

In this paper, the semi-orthogonal compactly supported spline wavelets are used as basis functions for the efficient solution of the thin-wire electric field integral equation (EFIE) in frequency domain. The method of moments (MoM) is used via the Galerkin procedure. Conventional MoM directly applied to the EFIE, leads to dense matrix which often becomes computationally intractable when large-scale problems are approached. To overcome these difficulties, wavelets can be used as a basis set so obtaining the generation of a sparse matrix; this is due to the local supports and the vanishing moments properties of the wavelets. In the paper, this technique is applied to analyze electromagnetic transients in a lightning protection systems schematized as a thin-wire structure. The study is carried out in frequency domain; a discrete fast Fourier transform algorithm can be used to compute time profiles of the electromagnetic interesting quantities. The unknown longitudinal currents are expressed by using multiscale wavelet expansions. Thus, the thin-wire EFIE is converted into a matrix equation by the Galerkin method. Results for linear spline wavelets along with their comparison with conventional MoM that uses triangular basis functions and the point matching procedure are presented, for two case studies. Good agreement has been reached with a strong reduction of the computational complexity.

SOIL IONIZATION DUE TO HIGH PULSE TRANSIENT CURRENTS LEAKED BY EARTH ELECTRODES

This paper proposes a numerical model of the soil ionization phenomena that can occur when earth electrodes are injected by high pulse transient currents, as the one associated with a direct lightning stroke. Based on finite difference time domain numerical scheme, this model ascribes the electrical breakdown in the soil to the process of discharge in the air. In fact, as soon as the local electric field overcomes the electrical strength, the air in the voids trapped among soil particles is ionized, and the current is conducted by ionized plasma paths locally grown. The dimension of these ionized air channels is strictly dependent upon the local temperature. Thus, a local heat balance is enforced in order to obtain the time variable conductivity profile of the medium. This model can be implemented both for concentrated and extended electrodes, since no hypothesis has to be enforced about the geometric shape of the ionized region. Validation of the proposed model is obtained by comparing simulation results with experimental data found in technical literature.

Physiological compatibility of wireless chargers for electric bicycles

The Inductive Power Transfer represents a viable solution of wireless battery charging for all users of electric mobility. This method brings some benefits to the electric vehicles, being a convenient technique, compared to the conventional wire-based battery charging. Among the electric vehicles, the electric bicycles particularly fit with this innovative method of battery charging. Nevertheless, the physiological effects of the produced magnetic fields need to be taken into account. In this paper, the design of an Inductive Power Transfer system for E-bike wireless battery charging is presented and the measurements concerning the surrounding magnetic field are provided in order to validate the model and evaluate the physiological compatibility of the system.

A smoothed particle interpolation scheme for transient electromagnetic simulation

In this paper, the fundamentals of a mesh-free particle numerical method for electromagnetic transient simulation are presented. The smoothed particle interpolation methodology is used by considering the particles as interpolation points in which the electromagnetic field components are computed. The particles can be arbitrarily placed in the problem domain: No regular grid, nor connectivity laws among the particles, have to be initially stated. Thus, the particles can be thickened only in distinct confined areas, where the electromagnetic field rapidly varies or in those regions in which objects of complex shape have to be simulated. Maxwells equations with the assigned boundary and initial conditions in time domain are numerically solved by means of the proposed method. Validation of the model is carried out by comparing the results with those obtained by the FDTD method for a one-dimensional (1-D) case study in order to easily show the capability of the proposed scheme

Evaluation of Radiated EMI in 42-V Vehicle Electrical Systems by FDTD Simulation

In this paper, a full 3-D numerical scheme based on the finite-difference time-domain method is used to predict the electromagnetic (EM) radiated interference generated by 42-V vehicle power electronic driven electrical loads. An experimental setup has been arranged in order to validate the proposed simulation tool. To this aim, the features of a semi-anechoic EM chamber have been exploited in order to operate in a shielded test site for the measurement of near-field radiated emissions. Two different 3-D geometrical configurations of realistic vehicle installations of the loads are studied. A comparative analysis among measured and computed results is performed. A good agreement between simulated and measured data is obtained. The proposed approach is suitable for the prediction of radiated EM interference generated by dc/dc converters and, particularly, by dual-voltage vehicle electric plants. In fact, due to the presence of complicated layout, the prediction of EM emissions can be a useful task in order to evaluate the EM compatibility (EMC) compliance from the design stage. Furthermore, with the growing market penetration of the ldquomore electric vehiclerdquo (MEV) concept in designing new vehicle electrical architectures, low-cost test methods for EMC assessments and suitable technical standard requirements have to be introduced. The proposed simulation tool can be usefully adopted to this aim. As an important advantage, it requires only a current measurement in the time domain. Such measurement does not need the use of a special test site or of a radiated field measurement setup.

A Meshfree Solver for the MEG Forward Problem

Non-invasive estimation of brain activity via magnetoencephalography (MEG) involves an inverse problem whose solution requires an accurate and fast forward solver. To this end, we propose the method of fundamental solutions as a meshfree alternative to the boundary element method (BEM). The solution of the MEG forward problem is obtained, via the method of particular solutions, by numerically solving a boundary value problem for the electric scalar potential, derived from the quasi-stationary approximation of Maxwells equations. The magnetic field is then computed by the Biot-Savart law. Numerical experiments have been carried out in a realistic single-shell head geometry. The proposed solver is compared with a state-of-the-art BEM solver. A good agreement and a reduced computational load show the attractiveness of the meshfree approach.

Simplified hybrid PD model in voids

In this paper a novel approach to model partial discharges (PD) activity taking place inside a spherical void in epoxy resin system has been traced. The approach is based on a time varying conductance of the inner void, subjected to multistress conditions: voltage, temperature and pressure. A simple lumped circuit macro-model simulates the global effects of PD activity: the different parameters influencing the discharge phenomenon in the void are taking into account by using a physical approach resulting in a time varying conductance inside the circuit. The evaluated PD activity has been compared with experimental and simulated one for the accessible and inaccessible part of the system. A discussion on the observed changes in PD activity has been reported.

The method of fundamental solutions in solving coupled boundary value problems for M/EEG

The estimation of neuronal activity in the human brain from electroencephalography (EEG) and magnetoencephalography (MEG) signals is a typical inverse problem whose solution process requires an accurate and fast forward solver. In this paper the method of fundamental solutions is, for the first time, proposed as a meshfree, boundary-type, and easy-to-implement alternative to the boundary element method (BEM) for solving the M/EEG forward problem. The solution of the forward problem is obtained by numerically solving a set of coupled boundary value problems for the three-dimensional Laplace equation. Numerical accuracy, convergence, and computational load are investigated. The proposed method is shown to be a competitive alternative to the state-of-the-art BEM for M/EEG forward solving.

A marching-on in time meshless kernel based solver for full-wave electromagnetic simulation

A meshless particle method based on an unconditionally stable time domain numerical scheme, oriented to electromagnetic transient simulations, is presented. The proposed scheme improves the smoothed particle electromagnetics method, already developed by the authors. The time stepping is approached by using the alternating directions implicit finite difference scheme, in a leapfrog way. The proposed formulation is used in order to efficiently overcome the stability relation constraint of explicit schemes. In fact, due to this constraint, large time steps cannot be used with small space steps and vice-versa. The same stability relation holds when the meshless formulation is applied together with an explicit finite difference scheme accounted for the time stepping. The computational tool is assessed and first simulation results are compared and discussed in order to validate the proposed approach.