Search results

The purpose of the paper is to show the application of the fixed‐point method with the T, Φ‐Φ formulation to get the steady‐state solution of the quasi‐static Maxwell's equations with non‐linear material properties and periodic excitations.

The fixed‐point method is used to solve the problem arising from the non‐linear material properties. The harmonic balance principle and a time periodic technique give the periodic solution in all non‐linear iterations. The optimal parameter of the fixed‐point method is investigated to accelerate its convergence speed.

The Galerkin equations of the DC part are found to be different from those of the higher harmonics. The optimal parameter of the fixed‐point method is determined.

The establishment of the Galerkin equations of the DC part is a new result. The method is first used to solve three‐dimensional problems with the T, Φ‐Φ formulation.

The purpose of this paper is to introduce a perturbation method for the A‐χ geometric formulation to solve eddy‐current problems and apply it to the feasibility design of a non‐destructive evaluation device suitable to detect long‐longitudinal volumetric flaws in hot steel bars.

The effect of the flaw is accurately and efficiently computed by solving an eddy‐current problem over an hexahedral grid which gives directly the perturbation due to the flaw with respect to the unperturbed configuration.

The perturbation method, reducing the cancelation error, produces accurate results also for small variations between the solutions obtained in the perturbed and unperturbed configurations. This is especially required when the tool is used as a forward solver for an inverse problem. The method yields also to a considerable speedup: the mesh used in the perturbed problem can in fact be reduced at a small fraction of the initial mesh, considering only a limited region surrounding the flaw in which the mesh can be refined. Moreover, the full three‐dimensional unperturbed problem does not need to be solved, since the source term for computing the perturbation is evaluated by solving a two‐dimensional flawless configuration having revolution symmetry.

A perturbation method for the A‐χ geometric formulation to solve eddy‐current problems has been introduced. The advantages of the perturbation method for non‐destructive testing applications have been described.

The purpose of this paper is to find out how to model iron losses in electrical machines accurately and efficiently.

The starting point was a previously developed vector hysteresis model that was designed and incorporated into the 2D time‐stepping finite‐element (FE) simulation of induction machines. The developed approach here is a decoupling between the vector hysteresis model and the 2D FE model of the machine. The huge time consumption of the incorporated hysteresis model required some new approach to make the model computationally efficient. This is dealt with through an a posteriori use of the vector hysteresis model.

In this research, it was found that the vector hysteresis model, although used in an a posteriori scheme is able to accurately predict the iron losses as far as these losses are small enough not to affect the other operation characteristics of the machine.

The research methods reported in this paper deal mainly with induction machines. The methods should be applied for transient operations of the induction machines as well as for other types of machines. The fact that the iron losses do not affect very much the operation characteristics of the machine is based on the fact that the air gap field plays a major role in these machines. The method cannot be applied to other magnetic devices where the iron losses are the main loss component.

The paper is of practical value for designers of electrical machines, who use FE programs. The methods presented here allow them to use a different FE package to simulate the machine and own routines (based on the presented methods) to predict the iron losses without loss of accuracy and in a reasonably short time.

The purpose of this paper is to present a new method to obtain robust solutions to electromagnetic optimization problems, solved with evolutional algorithms, which are insensitive to changes in design parameters such as spatial size, positioning and material constant.

Adjoint variable method is employed to evaluate the sensitivity of individuals in evolutional processes.

It is shown in the numerical examples, where the present method is applied to optimization of a superconducting energy storage system and C‐shape magnet, that robust solutions are actually obtained which are insensitive to deviations in spatial sizes.

Unlike usual optimization methods, the present method takes into account deviation in the design parameters due to production errors and long‐term changes. Moreover, the present method is limited to about twice the computational cost of non‐robust optimization methods.

The purpose of this paper is to investigate the possibility of utilizing printed circuit board (pcb) technology to manufacture coaxial transformers and to increase the predictability, accuracy and repeatability of the transformers leakage inductance.

The geometry of a coaxial transformer is approximated using pcb techniques. Several different geometries are presented with the outer coaxial conductor being approximated by discrete conductors varying from four to 36 in number. Finite element methods as well as experimental results are used to support the proposed ideas. A planar transformer is also analyzed in the same way to emphasize the design advantages offered by the proposed quasi‐coaxial transformer.

The proposed multi‐conductor structures can be applied as co‐axial transformers. The experimental values obtained for the leakage inductance of the coaxial structures correspond well to the predicted values. This is not the case for conventional planar structure where adjustments need to be made in the finite element analysis simulations to accommodate the shortcomings of the analytical calculations.

In applications where the prediction of the leakage inductance of a transformer is important, this method may be applied and has the advantage of conventional pcb manufacture techniques.

The purpose of this paper is to solve the electromagnetic scattering problem through a new integral‐based approach that uses the moving least squares (MLS) meshless method to generate its shape functions.

The electric field integral equation and its magnetic counterpart (MFIE) are discretized via special shape functions built numerically through the MLS procedure. This approach is applied to the particular problem concerning the scattering of a TM plane wave by an infinite conductor cylinder. An error norm is established in order to verify the quality of the obtained results.

Results show that the discretization process which employs MLS shape functions presents very good precision and fast convergence to the solution, when compared to results provided by another numerical method, the method of moments.

MLS shape functions occur in meshless methods intended to solve problems based on differential formulation. This paper shows that these shape functions can also be applied successfully to problems coming from an integral formulation.

The purpose of this paper is to extend a (μ/ρ, λ) evolution strategy to perform remarkably more globally and to detect as many solutions as possible close to the Pareto optimal front.

A C‐link cluster algorithm is used to group the parameter configurations of the current population into more or less independent clusters. Following this procedure, recombination (a classical operator of evolutionary strategies) is modified. Recombination within a cluster is performed with a higher probability than recombination of individuals coming from detached clusters.

It is shown that this new method ends up virtually always in the global solution of a multi‐modal test function. When applied to a real‐world application, several solutions very close to the front of Pareto optimal solutions are detected.

Stochastic optimization strategies need a very large number of function calls to exhibit their ability to reach very good local if not the global solution. Therefore, the application of such methods is still limited to problems where the forward solutions can be obtained with a reasonable computational effort.

The main improvement is the usage of approximate number of isolated clusters to dynamically update the size of the population in order to save computation time, to find the global solution with a higher probability and to use more than one objective function to cover a larger part of the Pareto optimal front.

The purpose of this paper is to present an approach to design passive loop systems in order to reach good performances.

The optimization has been performed by means of the MATLAB optimization toolbox “Gatool” which solves the optimization problems with a genetic algorithm.

Several configurations have been analyzed by varying the number of loops from 2 to 15, whose geometry has been chosen by the genetic algorithm. Considering a five loops configuration, along the reference path it is possible to obtain a shielding factor almost constant and equal to 3.5.

The optimized configurations have been compared with a practical employed layout composed of 17 closed loops placed above and around the junction zone. The shielding factors obtained by the six loops configuration are comparable with the ones of the practical layout.

The purpose of this paper is to present a method for analyzing higher magnetic force harmonics in electrical machines based on electromagnetic finite element simulation.

Sampling of air gap field solution data allows for a Fourier decomposition of magnetic forces and flux densities. A two‐dimensional convolution gives insight into the spectral decomposition of forces responsible for acoustic noise, vibration and higher torque harmonics.

The proposed approach seems especially suitable for synchronous machine models. The influence of magnetic circuit design parameters that are difficult to calculate analytically on the harmonic air gap content can be analyzed and the spectral force decomposition illustrated by means of space vectors.

The approach is generalized to the convolution and analysis of arbitrarily sampled two‐dimensional data in this paper.

The purpose of this paper is to devise a magnetic field modelling approach suitable for simulating the transient behaviour of a class of electromagnetic systems (particularly linear synchronous motors).

The classical 2D magnetic equivalent circuit (MEC) approach is extended by separately accounting for leakage flux from highly permeable polygonal regions (where the MEC approach is most applicable). It capitalises on the computational efficiency of an MEC approach for regions where the flux can be assumed to be uniformly channelled through a coarse network of “flux tubes” and accounts for leakage flux from these regions by introducing mutual permeances. These mutual permeances are geometry dependent and can be calculated upfront using a surface‐current representation of the magnetomotive force attributed to each flux tube.

As demonstrated with a simple example, the magnetic field solution converges with an increasing subdivision of flux tubes, yielding a transparent trade‐off between simulation time and accuracy.

Using Schwarz‐Christoffel mapping to approximate the mutual permeances is restrictive and introduces unnecessary error. Hence, the use of finite element or boundary element methods to obtain these permeances is under investigation. Furthermore, it is expected that introducing 2D flux tube elements for junction regions would be beneficial.

A novel approach is presented that aims to improve the accuracy of a traditional MEC solution, whilst retaining its computational advantage for the flux that is well channelled. The method has particular merit for the dynamic modelling of linear motors, where the machine's behaviour is dominated by the flux bridging the air gap.