Ebook: Computer Field Models of Electromagnetic Devices

This special issue of Studies in Applied Electromagnetics and Mechanics (by IOS PRESS) is devoted to papers presented at the International Symposium on Electromagnetic Fields in Electrical Engineering ISEF'09, organized jointly by the Laboratory of Electrical Systems and Environment (LSEE), University of Artois, France, and Institute of Mechatronics and Information Systems, Technical University of Lodz, Poland. The Conference venue was Arras, a city which is like an open-air museum, with its interesting history, architecture and heritage, including Flemish baroque squares, Art Deco buildings, a gothic Town Hall and a belfry, and many 18^th century monuments. The maze of underground tunnels offers special sightseeing opportunities. The venue was simply perfect for the conference.

The aim of ISEF symposia is to discuss recent developments in modelling and simulation, control systems, testing, measurements, monitoring, diagnostics and advanced software methodology in application to electrical and electronic devices and mechatronic systems. ISEF is a forum for applied mathematicians, computer and software engineers, and electronic and electrical engineers, to exchange ideas and experiences ranging from fundamental developments of theory to practical industrial applications. The conference is popular with academics, researchers and practising engineers.

Over the past 35 years ISEF has gained a prominent position in electromagnetic community. Since the first meeting in Uniejow Palace near Lodz in 1974 – organised as a National Symposium on “Electrodynamics of Transformers and Electrical Machines” – ISEF has travelled around Europe visiting, in addition to venues in Poland, several interesting places such as Pavia (twice), Southampton, Thessaloniki, Maribor, Baiona and finally Prague in 2007.

For the meeting in Arras, almost 300 papers had been submitted as digests and, after the reviewing process, 276 papers were accepted for presentation at the Conference. The short papers were published in the Book of Digests, while full versions included on a CD distributed to participants before the conference. Those versions were considered by session chairs for possible inclusion in the post-conference special issue.

The program of the conference comprised three invited papers, 5 oral and 8 dialogue sessions. The established conference topics were well represented, but supplemented by two new areas:

• artificial and computational intelligence,

• noise and vibration in electrical machines.

Another novelty was a special session with presentations by PhD students working in the field of electromagnetism. In fact, computational and applied electromagnetics is traditionally always strongly represented at ISEF by theoreticians, applied scientists and engineers, together offering a nice blend of fundamental methods, modelling techniques and practical solutions. We have no doubt that the small, but faithful, group of outstanding ‘electromagneticians’ regularly attending ISEF will continue to support future meetings providing a particular flavour and focus. But it is also very pleasing to see other areas emerging strongly as new conference topics, in particular computer engineering, software methodology, CAD techniques, artificial intelligence and material sciences.

The present special issue of Studies in Applied Electromagnetics and Mechanics contains 101 papers selected by the Guest Editors as a result of a two-stage qualification process: first, recommendations of the chairmen of the sessions, and secondly, reviews by two independent referees. Computational and modelling aspects feature prominently, although design, measurement and performance issues are addressed as well.

The papers selected for this volume, entitled: “Computer Field Models of Electromagnetic Devices”, have been grouped in three chapters which cover the above topics:

Chapter 1 Advanced Computational Techniques

Chapter 2 Recent Developments of Electromagnetic Devices

Chapter 3 Special Applications – Computational Electromagnetics

Chapter 4 Power Losses Computations

Chapter 5 Computer Modelling of Isolations Systems

The first chapter is devoted to fundamental and computational problems which appear in electromagnetics. The spread of topics and methods is very broad. Also, there are some papers in the chapter which show analytical solutions of the electromagnetic field problems. The analytical approach is nowadays mostly out of interest for researchers, especially those of younger generation but this attitude seems to be not supported by the reality of electromagnetism. The analysis of electromagnetic field sometimes requires deeper insight into the structure of mathematical model and this can be done just by means of analytical approach. The presented methods include analytical, numerical and hybrid methods. The development of calculation methods speeds up the calculation process significantly, on the other hand it triggers a temptation to solve the problems treated so far in simplistic fashion. The methods presented have been extensively illustrated with practical examples. Hybrid methods have been of particular interest. These methods combine virtues of various methods available, thus opening new opportunities.

The second chapter is devoted to problems widely discussed at many conferences, namely how to improve the techniques of optimal design of electromagnetic devices. The special attention has been paid to design of electrical machines. This chapter has been divided into a number of sub-chapters dedicated sequentially to induction machines, PM machines, Micro DC reluctance machines and drives. The overall chapter presents many new non-typical solutions resulting from the materials used, innovative constructions and technologies.

The third chapter contains papers which are a good mirror of what ISEF conference is. Most of these papers deal with some applications of electromagnetic field and the stress in these papers is put on the phenomena or devices or both. Computational technique is there just as a tool to understand the phenomena, to design a device or to know what hazards can occur. It seems to be very difficult, even impossible, to find some common idea which joins the papers in some groups because, in fact, each paper deals with its particular problem. We could stress that some specific problems, even electrical installation and anti-lightning protection, have been discussed. Prospective readers are recommended to look at this chapter very carefully and find the paper of their personal interest.

The fourth chapter was introduced at the request of the conference participants and was prepared with the assistance of specialists in the calculation of losses in electrical machines. It addresses a number of issues like shape and slot effect. Thanks to this a very good accordance of calculations and measurements has been achieved. It is to be noted that an accurate estimate of losses, as well as understanding of factors that create these losses enables the improvement of electrical machine design. Energy efficiency has become the key topic in recent years.

The sixth chapter addresses the issues of insulation and it's deterioration. It encompasses the problems of isolation materials, proposed methods of the isolation damage control and prevention of the internal short-circuit effects resulting from the isolation damage.

As Editors of this special issue we would like to express our thanks to IOS Press for giving us the opportunity to share the ISEF symposium with a wider community and to our many colleagues for their help, efficiency and valuable contribution to the reviewing process. At the end of these remarks let us, the Editors of the book, be allowed to express our thanks to our colleagues who have contributed to the book by peer-reviewing the papers at the conference as well as in the publishing process. We also convey our thanks to IOS Press Publisher for their effective collaboration in shaping this editorial enterprise. As ISEF conferences are organised biannually we do hope to keep our strong links with IOS Press in the future.

Ewa Napieralska-Juszczak, Chairman of the ISEF 2009, Organizing Committee

Sławomir Wiak, Chairman of the ISEF Symposium

In the paper a simulation of the stator end region using an axisymmetrical structure and the finite element methods was presented. The results allowed quick investigation of influence of different machine parameters and dimension, on core end packets, pressing fingers and clamping plate losses. The influence of the conductivity of clamping plate on inside losses was shown in the paper. Thermal coefficients were also calculated and based on scale law for temperature the temperature rice method estimation was establish.

The paper presents an analytical method which allows the estimation of the dynamic iron losses due to the slotting effect in a three phase induction machine. The case of a smooth air-gap machine supplied with nonsinusoidal waveforms is the subject of the initial developments. Their main interest is to show that elementary considerations, which are about the “copper” losses dissipated in stator and rotor cores, make it possible to find, in the case of rotating field, the usual formulations of the dynamic iron losses which appear in the literature. Then, this procedure is used to define the analytical expressions of the dynamic iron losses in case of sinusoidal supply taking the slotting effect into account. The calculus makes it possible to define these losses whether they originate from the fundamental or harmonic flux density waves distinguishing the effects according to stator or rotor core is considered. The variations of the different losses with the slip are given and it is shown that the slotting effect takes a non negligible part in the total dynamic iron losses. Moreover, it is shown that particular slotting flux density components, tied up with the slotting resonance phenomenon, have a main contribution.

The analysis of the iron loss distribution in the different parts of the machine makes it possible to define equivalent circuits of the induction machine iron cores. These circuits lead to estimate the steady harmonic torques generated by the iron rotor according to the iron rotor losses. Then, two particular experimental tests, which exploit the previous torques, allow the determination of all the parameters which intervene in all the components which define the total iron losses. Finally, the results of tests performed on an induction machine with rotor open windings and supplied stator, driven with a DC machine, are presented. The results validate the theoretical approach making clear that the slotting effect takes a non negligible part in the total iron loss definition.

For an electrical machine built with classical enameled copper wire, turn-to-turn capacitance variations can be used as an indicator of the insulation layer aging if it is correlated with standard indicators such as breakdown voltage or cumulative probability of failure at rated voltage. Such capacitance variations have a significant effect on the high frequency behavior of the machine winding which can be measured with the appropriate monitoring system.

The subject of the analysis is the quasi-stationary electromagnetic field near to the conductive wall subjected to arbitrary induction (electromagnetic waves; fields generated by currents flowing in conductors etc.). Solutions of Maxwell's equations in spectral Fourier's space we get in explicit analytic form; in a physical space calculation of field distribution, reduced to the calculation of integrals. The general formula of electric charge distribution on conductive surface is shown. Several examples illustrate the dependence of the charge on field frequency.

A new, semi-analytic method of calculation of the electromagnetic field distribution in bars of convex cross-cross-section, with sinusoidal current flowing, has been presented. By omitting the Maxwell's displacement current the only problem to solve is the Helmholtz equations within the bar and Laplace ones beyond it. The solution is in the form of function series, with coefficients calculated based on boundary conditions. These functions are being solved at the edge into the Fourier series, and by comparing them we obtain the algebraic linear equation system (solved numerically). In the article the results and illustration of calculations for the bar of elliptical cross-cross-section have been presented.

A novel analytical tools useful for the prediction and for the circuital representation of the rotating hysteresis phenomena in three-phase induction machines is proposed. The considered dynamic model, based on the space-vector d-q theory and on the use of complex permeability, does not need the application of the classic perturbative method for the introduction of a circuit element that describe the rotating power losses.

We provide an exact, simple and explicit analytical expression of corner reluctances for magnetic circuits of rectangular section. Obtained values are appreciably different from those obtained by making usual approximations. Besides, due to a decomposition of the solution in two terms which can be interpreted as an lengthening of the adjacent rectilinear legs, our expressions are very easy to use in order to compute reluctance of magnetic circuits, and thus also inductances and forces in magnetic devices, as well as magnetic losses. The present study applies also to electric and thermal resistances calculation. Although obtained expressions are rigorously exact only in the case of linear materials, this study allows also for flux and magnetic losses simplified calculation in the case of saturable materials. The accuracy of this simplified calculation is examined on a test structure by comparison with finite elements computation results.

The magnetic field occurring in the air gap of a surface permanent magnet (PM) machine is analytically modelled. The methodology is based on the use of some “field functions”, each of one representing the field waveform due to a particular source (PM or current) or anisotropy effect (slotting). Such field functions are identified by selective FEM magneto-static 2D-simulations, with a limited time consumption. The analytical model allows to reconstruct the air gap field with great accuracy, as verified by the comparison with numerous FEM simulations, both in no load and in loaded operating conditions.

The aim of this paper is to present the analytical method for the calculation of the three-dimensional end winding effect of asynchronous machine, this calculation is based on the application of Biot and Savart law at a three dimensional geometric end winding model of a squirrel cage asynchronous motor. For the taking account of this effect, an approach with this analytical calculation and the numerical bi-dimensional modelling of the machine, based with the finite element method, is presented. In this case the influence of the core iron in the end winding calculation is also considered.

The unbalanced magnetic pull is analytically modelled, referring to cylindrical rotor a.c. machines. Even if under some simplifying hypotheses (no homopolar flux, sinusoidal space distribution of the current density, no saturation, no parallel paths), various compact and significant expressions of field and force are obtained, for any number of pole pairs. Some FEM simulations and comparison with test data confirm the soundness of the proposed approach.

We developed a magnetic field analysis method for IPM motors using the three-dimensional finite element method with prismatic elements. This paper describes the accuracy and the calculation time of the method compared with that with tetrahedral elements, quantitatively. This paper also describes a numerical technique for permanent magnets division in an IPM motor.

The paper presents a mathematical model of the wheel vehicle drive system consisted with: special drive motor (radial induction motor, or PMSM motor) connected with drive transfer system, and drive elements (wheel axes). Magnetic fields distribution in traction motor, and tension of magnetic fields distributions in mechanical part of the vehicle are presented in the paper. Traction induction motors supplied with inverter decrease efficiency of the motor and sometimes present additional rotor and stator fault. Modern diagnostics method used of: FEM, BEA and random method has been used for faulty motor simulation and shows results of motor fault effects. Experimental results collaborate with the simulation and theoretical effects. ANSYS, JMAG and FEMM computer programs were applied in calculation of magnetic fields distribution for different faults state of the motors. On the base of magnetic field and force tension distributions were analyzed different failures situations and method of limitation their negative effects. Some laboratory experiments was realized for the traction motor.

An accuracy-controllable alternating-direction implicit finite-difference time-domain method is presented in this paper for the efficient modeling of integrated semi-conductor circuits and printed circuit boards in modern EMC structures. Preserving the formulation of the conventional algorithm, the novel 3-D concept introduces supplementary nodes in terms of a convex stencil procedure in order to significantly suppress the detrimental dispersion errors due to the Courant limit cancellation. Thus, instead of utilizing the typical derivative approximators, a set of weighted interpolating polynomials, which do not increase the overall algorithmic complexity, is derived. Numerical results, obtained for various time-steps, are compared to reference solutions or measurement data, revealing the limitations of existing schemes and the advantages of the proposed technique.

The Fourier integral transformation method for determination of coupling capacitances in the selected conductive paths' system is presented in this paper. It is a continuation of investigations [1], which concerned the identification problems of capacitive couplings in hybrid microcircuits. The capacitance calculation is based on its definition. Electrical potential presented in form of Fourier integrals fulfills the Laplace's equation. Resulting from here the equation system of electric charge distribution is solved numerically using the collocation method. On this basis the capacitance between conducting paths are calculated and partially experimentally verified

Magnetic field distribution is determined by applying Equivalent Currents Method (ECM). The Green's function for magnetic vector potential of the infinite linear conductor with steady current, placed in free space, on the boundary of two magnetic materials, is used. In this paper, the authors applied a technique based on substituting Ampere's microscopic currents with total currents. Due to combination of numerical and analytical determination, this is a hybrid method. Together with Equivalent Electrode Method (EEM), this method can be applied for magnetic field calculations of systems with both metal electrodes and many different homogenous magnetic materials.

The common-mode impedance over a wide frequency range is of high interest for the analysis of parasitic phenomena occurring with inverter-fed machines. Here, a method is presented to model the common-mode impedance of electrical machines by a transmission-line model. The parameters are determined by finite-element calculations and by a combined analytic finite-element approach. The results illustrate the significant influence of the current return path through the laminated stator core back stack as well as the role of the winding overhang.

Recent progress in material science has made it possible to economically implement motors with permanent magnet technology in a direct drive system. Particularly synchronous motors with interior permanent magnets benefit from this development. This paper offers a fast and accurate analysis methodology that is suitable for use in an everyday design environment. It uses both the analytical and finite element method (FEM) and is verified by means of a prototype traction motor. From the results, it is concluded that three two-dimensional functions can be used to accurately calculate the performance of permanent magnet motors in an everyday design environment.

This paper investigates an optimal design of a double-sided iron core type permanent magnet linear synchronous motor (PMLSM) for ropeless elevator system using response surface methodology (RSM). An inherent drawback of the PMLSM is the detent force that will generate the pulsations of the propulsion force, deteriorate the smoothness of motion drive, and make passengers feel nervous. To solve the force pulsations the combination of two dimensional (2D) finite element analysis (FEA) and RSM is utilized, which can solve the problem effectively without much time consuming. The validity and effectiveness are verified by some numerical calculations.

The aim of this paper is the computation of electromagnetic fields radiated by lightning witch is necessary in order to protect effectively the electrical and electronic systems against disturbances caused by this kind of discharges. In this paper we propose a hybrid method to evaluate the electromagnetic field associated to lightning return stroke current. This method is the combination of the images method and finite difference time-domain (FDTD) method. We calculate first, the magnetic field with images method (using the Simpson integration numerical method), and, secondly, the electric field based partially on the FDTD method. The lightning return stroke current is modeled by the engineering models. In this study we compare five lightning return stroke current models, namely the Transmission Line (TL) model, the Modified Transmission Line with exponential decay (MTLE) model, the Modified Transmission Line with linear decay (MTLL) model, Traveling current Source (TCS) model, and Bruce and Gold model (BG) model by assuming a common current wave shape at the channel base. In this work we have presented the influence of the variable speed of the return stroke current and the variable factor λ of the MTLE model on the computation of lightning electromagnetic field.

This paper presents an analytical model for prediction of on load magnetic field in slotted surface mounted permanent magnet radial flux synchronous machines. This technique can either be used in the case of internal or external rotor radial-field machines topologies. The machine model is formulated in polar coordinates and accounts explicitly for the stator windings current waveform and effect of stator slotting. Results from this analytical model are compared to corresponding finite element analyses. This analytical model is then coupled to electrical circuit equations to study the behaviour of a PM synchronous alternator connected to a power rectifier.