O. Bottauscio

Modeling of electromagnetic phenomena in soft magnetic materials under unidirectional time periodic flux excitations

We report on recent advances in the modeling of magnetic losses in steel laminations used in electromagnetic devices. The integrated-lamination moving dynamic Preisach model, used to evaluate the dynamic magnetization loops under distorted unidirectional flux patterns, is described. The main goal is the comparison of two numerical procedures, using the finite element-finite difference technique and the finite element-fixed point technique, respectively, each properly taking into account the hysteresis characteristics by the Preisach theory. Moreover, attention is paid to the identification of the material parameters entering the moving dynamic Preisach model. Finally, the two techniques are validated by the comparison of numerical experiments and measurements on two different materials. Here, global as well as local quantities in the lamination structure are evaluated.

Power losses in magnetic laminations with hysteresis: Finite element modeling and experimental validation

Dynamic hysteresis loop shapes and magnetic power losses are studied in nonoriented Fe-Si laminations exhibiting significant excess losses. Measurements are carried out under controlled sinusoidal induction in the frequency range from 1 Hz to 1.6 kHz, at various peak inductions from 0.25 to 1.5 T. Excess losses are found to obey a f3/2 law up to frequencies of 200–400 Hz, depending on peak induction. Beyond this limit, definite deviations are observed, due to eddy current shielding. Detailed information on the flux and field distribution in this high frequency regime is obtained by finite element solutions of Maxwell equations employing the dynamic Preisach model to describe quasi-static hysteresis and dynamic wall processes. The agreement between theoretical predictions and measurements is discussed.

Preisach Type Hysteresis Models in Magnetic Field Computation

Abstract The paper illustrates the evolution of Preisach-type models of hysteresis, involving mean field effect, dynamic effect and vector behaviour and their capability to be included into finite element electromagnetic field computation. The study makes reference to 1D and 2D formulations developed under different simplifying assumptions. Particular attention is devoted to the use of fixed point technique which is found to be very advantageous for the solution of hysteretic problems. Some examples of the analysis of magnetic field problems with hysteresis are finally presented.

Analysis of laminated cores through a directly coupled 2-D/1-D electromagnetic field formulation

Summary form only given. One of the most critical aspect in the modelling of laminated cores is the capability to evaluate the influence of the skin effect in the lamination depth on the magnetic flux distribution in the sheet plane. On this subject, the authors have already presented a computational procedure, based on a standard vector potential 2D magnetic field solution, which accounts for the effects of eddy currents flowing along the rolling plane both for unidirectional and for rotational fluxes. The proposed procedure handles the diffusion phenomena in the lamination depth by means of a dynamic magnetic model, consisting of the solution of 1D electromagnetic field problems defined in the sheet thickness. The linkage between the 2D (xy-plane) and 1D (z-axis) electromagnetic problems requires the use of two nested iterative Fixed Point (FP) schemes. Here an alternative approach is proposed, by directly coupling the equations governing the 2D and 1D electromagnetic field problems, to reduce the computational burden of the entire algorithm, without affecting the result accuracy.

Analysis of isotropic materials with vector hysteresis

This paper presents the implementation of an isotropic vector hysteresis model within a two dimensional time periodic finite element procedure, formulated in terms of magnetic vector potential. The standard vector Preisach Model is employed and an identification procedure based on the scalar Preisach distribution function is used. Nonlinearity is handled by means of the fixed point technique following the H-convergence scheme. The convergence of the procedure is assessed and the results obtained are discussed.

A hysteretic periodic magnetic field solution using Preisach model and Fixed Point technique

The paper presents a computational approach for periodic magnetic field problems including hysteresis. The procedure is based on the finite element method combining scalar Preisach model with Fixed Point technique. The computational scheme is applied to a one-dimensional model problem. The results are validated by comparison with the exact analytical solution.

Loss separation analysis in ferromagnetic sheets under PWM inverter supply

A Finite Element model is used to investigate the influence of different PWM parameters on iron loss components. It is found that only the classical losses are sensibly affected by the supply waveform. The predictions are validated by the experiments. Finally, a comparison with an analytical approach is presented.

A micromagnetic study of the reversal mechanism in permalloy antidot arrays

A numerical analysis is focused on the influence of patterning and finite-size effects on the hysteresis properties and magnetization reversal of permalloy antidot films with square lattice and square holes. Simulations are performed by solving the Landau-Lifshitz equation. The aim is to explain the relationships between the shape of the hysteresis loop and the different stages of the reversal process. In particular, the switching mechanism is characterized by the nucleation of domain chains that destroy the periodic symmetry in the magnetization present when infinite periodicity is considered. This behavior is strongly influenced by the demagnetizing effects arising both at the film boundaries and at the hole edges.

Passive and active electromagnetic shielding of induction heaters

In induction heaters, a metallic workpiece is heated by eddy currents, induced by strong alternating magnetic fields. Using numerical models, proper active and passive shields are designed in order to mitigate the stray field of the induction heater. Two models are presented: an axisymmetric finite-element (FEM) and a hybrid finite-element-boundary-element (FEM-BEM) model. Results of both numerical methods are compared and verified with measurements on an induction heater archetype. A good correspondence is observed. Combination of passive and active shielding results in almost 20-dB field reduction.

Power losses in thick steel laminations with hysteresis

Magnetic power losses have been experimentally investigated and theoretically predicted over a range of frequencies (direct current—1.5 kHz) and peak inductions (0.5–1.5 T) in 1‐mm‐thick FeSi 2 wt. % laminations. The direct current hysteresis properties of the system are described by the Preisach model, with the Preisach distribution function reconstructed from the measurement of the recoil magnetization curve (Bp=1.7 T). On this basis, the time behavior of the magnetic induction vs frequency at different lamination depths is calculated by a finite element method numerical solution of Maxwell equations, which takes explicitly into account the Preisach model hysteretic B(H) relationship. The computed loop shapes are, in general, in good agreement with the measured ones. The power loss dependence on frequency is predicted and experimentally found to change from a ∼f3/2 to a ∼f2 law with increasing peak induction.