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This paper proposes an adaptive equivalent RL-circuit model for eddy-current devices with a single electrical port (one terminal voltage and current) and translational movement. The device is first characterised by means of frequency-domain finite-element computations in the relevant frequency and position intervals, for subsequently fitting constant-coefficient RL-ladder circuits of adjustable size (i.e. variable number of branches and loops). The accuracy of the ladder-circuit model is assessed in both frequency and time domain. The time-varying position involves the force computation from the circuit and the coupling with the mechanical equation. By way of validation, we study the axisymmetric magnetic-levitation device of TEAM Workshop problem 28. Results exhibit good convergence to reference finite-element ones with the increasing number of branches. ispartof: Ieee Transactions On Magnetics vol:58 issue:9 status: Published online

In this paper, classical approaches to evaluate leakage reactance in power transformers, that is, the simple analytical model, the Rogowski and the Stephens methods, are compared with each other and its limitations are exposed. To generalize and to improve the accuracy of the transformer leakage reactance evaluation, the authors propose a new analytical approach whose parameters are determined using curve fitting method from solutions obtained by 2D Finite Element Method (FEM) simulations. Since these parameters depend on the transformer windows and windings dimensions, its values are determined using per unit systems and also for typical transformer height to width ratio from 2 to 4. Consequently, the proposed method can be applied directly for the leakage reactance calculation without performing FEM simulations and for a large family of transformers with different windings configurations. The proposed method is thus compared with the classical approaches and its results show a good agreement compared with those obtained through 2D FEM simulations for any window and winding configurations.

Power converters are an essential part of modern power systems, giving flexibility to the power transportation and allowing the insertion of a wide range of different energy sources. One drawback of the converters is that the supraharmonic conducted emissions introduced by them can compromise the stability of these systems through electromagnetic interference (EMI). Electromagnetic compatibility (EMC) filters are used to prevent such problems. Nevertheless, these filters are designed to respect standards based on measurements in conditions considerably different from real applications. Particularly, if a converter is connected to electrically long cables its conducted emissions may be amplified by the resonance phenomenon. The method described in this paper allows the definition of a range for the filters input impedances where the conducted emissions in a long cable will not be amplified beyond established levels. In some cases the method allows the visualization of three-dimensional surfaces indicating the magnitude, frequency and position of the resonance phenomenon. In the general case these surfaces are defined on higher dimensions and can be analyzed with deterministic optimization algorithms. The originality of this paper resides in the generalized analysis of the resonance phenomenon, that it is based on frequency-dependent cable parameters and applies to unbalanced systems.

This work points out the origin of the convergence problem when the Jiles-Atherton hysteresis model is associated with the finite elements method (FEM) to analyze electromagnetic devices. To overcome this problem, a restriction is proposed and applied in the classical approach for the determination of the Jiles-Atherton hysteresis model parameters process. The presented methodology considers the inverse model, where the magnetic induction is the input variable and the magnetic field is the output variable.

International audience

WOS:000599506500051; International audience; A novel numerical analysis to characterize and to visualize the resonance behavior in a long cable is proposed. The resonance-due maximum amplification, and the frequency and position to which the maximum occurs, are represented in function of the load connected to the cable terminal in a 3-D plot here denominated "resonance surface response." This analysis is based on a white box modeling and allows the design of protective measures against the resonance phenomenon, such as filter design, protection against cross-talk, adequate voltage insulation choice, etc. One of these applications is exemplified: the design of an output filter for a power converter connected to a long cable, from which the results are compared to a classical design of the same filter to highlight the advantages and demonstrate the robustness of the proposed technique.

Purpose This paper aims to develop a methodology for progressive finite element (FE) modeling of transformers, from simple to complex models of both magnetic cores and windings. Design/methodology/approach The progressive modeling of transformers is performed via a subproblem (SP) FE method. A complete problem is split into SPs with different adapted overlapping meshes. Model refinements are performed from ideal to real flux tubes, one-dimensional to two-dimensional to three-dimensional models, linear to nonlinear materials, perfect to real materials, single wire to volume conductor windings and homogenized to fine models of cores and coils, with any coupling of these changes. Findings The proposed unified procedure efficiently feeds each SP via interface conditions (ICs), which lightens mesh-to-mesh sources transfers and quantifies the gain given by each refinement on both local fields and global quantities, with a clear view on its significance to justify its usefulness, if any. It can also help in education with a progressive understanding of the various aspects of transformer designs. Originality/value Models of different accuracy levels are sequenced with successive additive corrections supported by different adapted meshes. The way the sources act at each correction step, up to the full models with their actual geometries, is given a particular care and generalized, allowing the proposed unified procedure. For all the considered corrections, the sources are always of IC type, thus only needed in layers of FE along boundaries, which lightens the required mesh-to-mesh projections between subproblems.

This paper compares the performance of the popular adaptive $h$ -refinement ( $h\text{R}$ ) technique for the finite-element method (FEM) with the adaptive version of the recently presented operator-customized wavelet basis (OCWB). This new method is a combination of the second-generation wavelet theory with hierarchical basis, which is a multi-resolution basis, and, when applied to the FEM, the solution is split into different levels of detail. These levels, also referred to as scales, are composed by compactly supported functions, allowing the detail to be added only on the chosen regions. Although this strategy reduces the total system dimension with sufficiently small error, all the scales are naturally coupled, which means that there are interactions between functions composing different detail levels. This coupling forces the whole multi-resolution system to be recomputed when a detail is added, a kind of redundancy that also occurs on the $h\text{R}$ method. Using the second-generation wavelet theory, functions are custom-designed to decouple the system, which means the interactions between the functions of different levels are eliminated, and it is possible to solve for further detail independently of previous scales. This property significantly increases the performance of the algorithm. Conversely, the formulation—and, consequently, the algorithm design—complexity is also increased, which is the reason why there are such few applications on the subject. Like the $h\text{R}$ method, an adaptive OCWB can be programmed with various strategies; since the results are shown in terms of processing time on a regular PC, both the algorithms have been developed with similar structures.

This paper discusses the implementation of the inverse Jiles–Atherton vector hysteresis model with the 2-D Finite Element Method (FEM) for the analysis of an induction machine operating as self-excited generator. A differential reluctivity tensor couples the hysteresis model with the magnetic vector potential-based finite-element model. Experimental and simulated results (transient and steady state) are presented.

WOS:000487045600005; International audience; A complete modeling technique for unshielded power cables is proposed. The focus is on applications where the resonancephenomena take place in electrically long cables and is originated from periodic excitation, such as power converters.The resonance problems caused by switching converters tend to become more common with the advent of wide band gapsemiconductors. This paper includes a new experimental protocol specific for unshielded power cable parameter identificationin a wide frequency band, from DC up to medium frequencies (tens of MHz), with an impedance analyzer. It also introduces afrequency-domain simulation tool with conversion to the time domain, via the Fourier series. This frequency-domain modelingis straightforward, and its accuracy depends only on the accuracy of the cable parameter identification.

International audience; The Facet finite-element method (FFEM) requires a source field solution that is commonly obtained by the Biot-Savart (BS) equation that can be time-consuming. The subproblem modeling is applied to the FFEM in order to minimize the computational effort and time necessary to obtain the solution. The volume sources, which allow solving the BS equation only along the active regions, are presented, as well as the BS boundary condition correction.

The need for models that represent the behaviour of transformers operating in steady state or submitted to transient events is of great importance in studies involving power systems. In this context, this study presents a model used to represent the impedance frequency response of transformers at no load and under nominal conditions. In the model, networks of parameters with RLC cells are employed to reproduce the resonances present in the frequency responses and also RL network sections are used to represent the frequency-dependent effects in the core, which aid in the current damping during transient events. The parameter values of these networks are determined with the least-squares numerical method. To evaluate the model as well as the methodology to determine the parameter values, data originating from measurements of the frequency responses with frequency range from 10 Hz to 2 MHz of two single-phase transformers (16 kVA and 55 MVA) are used. Validations of the model are carried out in the frequency and time domains. The model can be used to simulate transformer operation under nominal conditions of voltage and frequency and also for a broad frequency spectrum.

International audience; This paper considers the resonance phenomena observed on cables connected to power converters, evaluating theoretically and experimentally the voltage amplification due to resonance on these cables. The experimental study was effectuated on cables typically used on industrial applications. Factors restricting resonance-due amplifications are considered, as well as the conditions under which resonance issues may rise in such systems.

International audience; A 3-D finite-element method mesh is converted to a reluctance network through an original magnetostatic formulation based on facet shape functions interpolation of the magnetic induction. This network is coupled with a standard reluctance network, characterizing a 0-D system and solved by a circuit solver approach.

International audience; The paper proposes an optimization approach to address the modeling and sizing complexities of Brushless Doubly-Fed Reluctances Machines. A semi-analytical model and a reluctance network model are coupled to a deterministic optimization algorithm where several inputs and outputs parameters can be constrained to solve system equations iteratively by maximizing or minimizing an objective function. A Pareto Front strategy is used to illustrate the model capabilities, highlighting the trade-offs on the design of this kind of electrical machines. The optimization model provides fast results to define an initial design, reducing the number of unknown parameters of early development stages. This saves computation time and computer resources in the design process compared to Finite Element Analysis.

This paper presents an equipment dedicated to the monitoring of synchronous generator through the measurements of the external magnetic field time derivative. The equipment uses a methodology which can be an additional technique to those applied currently on the faults detection, mainly when monitoring the incipient faults type. Based on frequency spectra (magnetic signatures), the faults detection is performed by the analysis of the components evolution. As it is not possible to test the ability of the equipment in detecting several types of faults of generators faults in a power plant, a testbench was constructed for this purpose. Faults inserted deliberately in the generators of the testbench are detected by the equipment, showing its capacity. This equipment has been also installed in power plants.

A subproblem finite element method is developed for modeling the transformer core joints. It applies magnetostatic and magnetodynamic models on progressive geometries and different components of the solution, supported by different meshes. It allows an efficient and robust analysis of magnetic circuits in any frequency range, with an accurate calculation of flux density, losses, reluctance, and impedance in transformer core joint zone. The models of the study properly account for the effects of core design parameters such as length of air gaps and overlap length in stacked-lamination cores. The proposed models, which include saturation, are applied to grain-oriented silicon steel and two types of step-lap joints are considered: single-step-lap (SSL) joints and multistep-lap (MSL) joints. The values of magnetic reluctance, impedance, and Joule losses obtained with SSL joint are bigger than with MSL joint.

A 3D Finite Element Method (FEM) mesh is converted to a reluctance network through an original magnetostatic formulation based on face shape functions interpolation of the induction. This network is coupled with a standard reluctance network, characterizing a 0D system and solved by a circuit solver approach.

This paper discusses the implementation of the inverse Jiles-Atherton vector hysteresis model with 2-D finite element (FE) method for the analysis of a hysteresis motor electromechanical behavior. A differential reluctivity tensor couples the hysteresis model with the magnetic vector potential-based FE model. Simulation results are validated by experimental data obtained from a specially designed machine.

International audience; Progressive refinements of the current sources in magnetic vector potential finite element formulations are done with a subproblem method. The sources are first considered via magnetomotive force or Biot-Savart models up to their volume finite element models, from statics to dynamics. A novel way to define the source fields is proposed to lighten the computational efforts, via the conversion of the common volume sources to surface sources, with no need of any pre-resolution. Accuracy improvements are then efficiently obtained for local currents and fields, and global quantities, i.e. inductances, resistances, Joule losses and forces.

In this paper, the authors deal with the finite-element (FE) modeling of eddy-current effects in form-wound windings of electrical machines using a previously proposed general frequency- and time-domain homogenization method. By way of demonstration and val- idation, a real-life 1250-kW induction machine with double-layer stator winding is considered. The skin and proximity effects in one stator conductor (copper bar) are first quantified by means of a simple low-cost FE model, leading to complex and frequency-dependent coefficients for the homogenized winding (reluctivity for proximity effect and conductivity or resistance for skin effect). These com- plex coefficients are subsequently translated into real-valued and constant coefficients that allow for time-domain homogenization when introducing a limited number of additional degrees of freedom in the FE model. All results obtained with the homogenized model (con- sidering one conductor or a complete slot) agree well with those produced by a brute-force approach (modeling and finely discretizing each conductor). ispartof: IEEE Transactions on Magnetics vol:46 issue:8 pages:2852-2855 ispartof: location:BRAZIL, Santa Catarina status: published

This study has analyzed the performance of an alternating electric current measuring system using a Rogowski coil as a transducer, applied to magnitudes of milliamps to hundreds of amperes. It has been noticed that for low amplitudes, as well as for low frequencies, noise interferes with precision. For operation levels with a better signal-to-noise rate, the results presented agreements with those from a Hall effect current probe. Although prototypes have been carefully constructed, performance can be improved by the use of more appropriate winding techniques as well as through improvement in electronic circuits.

This paper deals with the electromagnetic modeling and design aspects of brushless doubly fed reluctance machines (BDFRM). It presents the development and the experimental validation of a semi-analytical model (SAM) used for sizing new machine designs. The SAM is an optimization-oriented model implemented using analytical approaches and a deterministic optimization algorithm to find an optimal machine by solving iteratively an objective function, whereas satisfying several output constraints simultaneously. It is fast and accurate for pre-design stages, premises that are confirmed by both simulation and experimental results.

In this paper a magnetic vector hysteresis model based on Play hysterons is presented. This model allows the evaluation of the magnetic induction vector from an imposed magnetic field vector. The proposed methodology is simple to implement and needs only a small set of experimental data. Some aspects of the model are discussed and an experimental validation is performed

In this paper we propose an original system for replacing batteries or feeding cables used to feed monitoring equipments exposed to stray magnetic fields. The main elements of this system are a coil intended to capture the energy from magnetic field and an electronic circuit for voltage controlling. Two voltage control systems are presented: a DC–DC converter yielding a regulated voltage and a voltage tripler circuit carrying a load capacitor. This system furnishes approximately 10 mW depending on the field magnitude and the coil core material. It is shown that the low consumption feeding circuit is effective and the use of core material may increase the furnished power to up to 25 %.

This paper presents a new model for prediction of wave propagation in indoor and outdoor environments. The method is based on two-dimensional ray-tracing techniques using image theory to determine all valid paths. The computation of fields is based on geometrical optics and uniform theory of diffraction. A new approach for transmitted rays through the walls is proposed and validated by comparison with results obtained via the finite-difference time-domain method. Results for a practical indoor environment are presented by mapping the received power

Dual finite element formulations are developed for modeling both inductive and capacitive effects in massive inductors. Mixed finite elements are used to satisfy each chosen conformity level for the unknown fields and to naturally define the global quantities involved in the inductive and capacitive circuit relations, to be used in circuit coupling. The interest of satisfying conformity properties for the considered magnetic and electric coupled problems is shown and the related mathematical and discrete tools for any wished conformity level are developed

A new anisotropic magnetic hysteresis model based on the Prandtl operators is proposed. This model is suitable to calculate the magnetic vector field H from an imposed vector induction B. The model is easy to implement, requiring little computational effort with a small set of material parameters. The methodology is validated by comparing experimental and calculated results.

This paper presents a method to analyse electrical machines considering simultaneously the electromagnetic field, electric circuit, control loop, movement and skewing effects. The major contribution of this work leans on its generality, i.e. it can be applied to electrical machines connected to static converters submitted to any control laws, avoiding an a priori analysis. Simulation results of a three‐phase Brushless AC (BLAC) motor fed by a PWM converter is presented as well as a comparison of simulation and experimental results obtained using a two‐phase‐on converter were also presented.

In this paper, we present a new vector hysteresis model, which is derived from the original Jiles-Atherton scalar one. The model presents the magnetic vector induction as the independent variable. A modified Langevin equation is used to represent the anhysteretic vector magnetization, and some model aspects are discussed. A comparison between measured and calculated curves for an anisotropic soft magnetic material is performed to validate the model.

The parameters set of the Jiles-Atherton hysteresis model is identified by using a real coded genetic algorithm. The parameters identification is performed by minimizing the mean squared error between experimental and simulated magnetic field curves. The procedure is validated by comparing experimental and simulated results.

A model allowing the simulation of induction machines with different rotor bars configurations is presented. The electrical machine is modeled by using two-dimensional (2-D) finite-element method and its equations are directly coupled with those of the circuit. A general and new contribution is added for the consideration of special rotor bars topologies. The movement is taken into account by means of the moving band technique, the Maxwell stress tensor, and the mechanical oscillation equation. The model is applied to a brushless doubly fed induction motor.

An original and easy‐to‐implement method to take into account movement (motion) in the 2D harmonic balance finite element modelling of electrical machines is presented. The global harmonic balance system of algebraic equations is derived by applying the Galerkin approach to both the space and time discretisation. The harmonic basis functions, i.e. a cosine and a sine function for each nonzero frequency and a constant function 1 for the DC component, are used for approximating the periodic time variation as well as for weighing the time domain equations in the fundamental period. In practice, this requires some elementary manipulations of the moving band stiffness matrix. Magnetic saturation and electrical circuit coupling are considered in the analysis as well. As an application example, the noload operation of a permanent‐magnet machine is considered. The voltage and induction waveforms obtained with the proposed harmonic balance method are shown to converge well to those obtained with time stepping.

An optimization procedure to obtain the parameters of both the original Jiles-Atherton and the inverse Jiles-Atherton hysteresis models is presented in this paper. Doing so, minor loops can be conveniently simulated without inserting scaling methods. The comparison between experimental and calculation results validates the procedure.

International audience; Purpose – The purpose of this paper is to develop a subproblem method (SPM) for progressive modeling of inductors, with model refinements of both source conductors and magnetic cores.Design/methodology/approach – The modeling of inductors is split into a sequence of progressive finite element (FE) SPs. The source fields (SFs) generated by the source conductors alone are calculated at first via either the Biot-Savart (BS) law or FEs. With a novel general way to define the SFs via interface conditions (ICs), to lighten their evaluation process, the associated reaction fields for each added or modified region, mainly the magnetic cores, and in return for the source conductor regions themselves when massive, are then calculated with FE models. Changes of magnetic regions go from perfect magnetic properties up to volume linear and nonlinear properties, and from statics to dynamics.Findings – For any added or modified region, the novel proposed ICs to define the SFs appear of general usefulness, which opens the method to a wide range of model improvements.Originality/value – The resulting SPM allows efficient solving of parameterized analyses thanks to a proper mesh for each SP and the reuse of previous solutions to be locally corrected, in association with novel SF ICs that strongly lighten the quantity of BS evaluations. Significant corrections are progressively obtained for the fields, up to nonlinear magnetic core properties and skin and proximity effects in conductors, and for the related inductances and resistances.

An efficient and robust time discretization procedure of theta type is proposed in the frame of the finite element‐circuit equation coupling for electronic circuits with switches, i.e. the use of diodes, thyristors and transistors. This procedure enables the use of the Crank‐Nicolson scheme whatever the circuit and its working conditions by eliminating the undesirable oscillations of the solution peculiar to this scheme. It is based on the accurate determination of the switching instants and on a local modification of the theta parameter.

This paper presents a method for direct coupling electrical machines, represented by two-dimensional (2-D) finite elements with the external circuit. The movement is taken into account by means of the moving band technique. The field and circuit equations are calculated automatically and then solved simultaneously using a time step procedure. The major contribution of this work is the fact that the whole system is calculated automatically, i.e., the electromagnetic field (Maxwell equations) and the converter circuit (Kirchhoff voltage and current laws and the elements characteristics equations) are strongly coupled in a unique set taking into account the movement. In order to validate the implemented procedure, a permanent magnet generator feeding a flyback converter is simulated and tested.

This paper presents the analysis of a tubular linear induction motor (TLIM) taking into account the movement. A translational moving band is used. Calculated results are validated by practical measurements.

International audience; Purpose - This paper seeks to develop a sub-domain perturbation technique to efficiently calculate strong skin and proximity effects in conductors within frequency and time domain finite element (FE) analyses. Design/methodology/approach - A reference eddy current FE problem is first solved by considering perfect conductors. This is done via appropriate boundary conditions (BCs) on the conductors. Next the solution of the reference problem gives the source for eddy current FE perturbation sub-problems in each conductor then considered with a finite conductivity. Each of these problems requires an appropriate volume mesh of the associated conductor and its surrounding region. Findings - The skin and proximity effects in both active and passive conductors can be accurately determined in a wide frequency range, allowing for precise losses calculations in inductors as well as in external conducting pieces. Originality/value - The developed method allows one to accurately determine the current density distributions and ensuing losses in conductors of any shape, not only in the frequency domain but also in the time domain. Therefore, it extends the domain of validity and applicability of impedance-type BC techniques. It also offers an original way to uncouple FE regions that allows the solution process to be lightened, as well as efficient parameterized analyses on the signal form and the conductor characteristics.

International audience; The Brushless Doubly-Fed Reluctance Machine (BDFRM) is a potential candidate to compete with induction and permanent magnet machines in variable speed application such as wind power. It is in research phase and much effort, mostly on its electromagnetic design, is still needed so that this machine can be used in large scale. This paper focuses on rotor design by studying the impact of geometric parameter variations on its global performance by using Finite Element Analysis (FEA). Issues with the flux barrier ending's geometry, number of rotor slots, existence of an additional interpolar flux barrier, rotor slot arc angle and duct ratio are investigated. The results show potentially good practices that should be considered on BDFRM rotor design. They may also be used as initial step for a more refined optimization process using specialized tools

Considering the importance of modeling the electri- cal power system behavior under high frequency transients, this paper aims to present a practical methodology to obtain a RL lumped parameters model of an air-cored reactor. Firstly, the RL frequency responses are obtained using the Finite Element Method (FEM). Thus, the frequency response is converted into a RL circuit in accordance with the classical series Foster model and its parameters values are calculated through Least Square (LS) fitting algorithm. Finally, the lumped parameters circuit is converted to an ATP network model. For validation purposes a well-known air-cored reactor is modeled for a frequency range from 10 Hz to 100 kHz and the frequency responses obtained with FEM, LS fitting and ATP are compared. Index Terms—Frequency response, Finite Element Method, Least Square, ATP, Air-cored reactor