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The paper deals with the design by optimization in pre-sizing step of a drive system that combines a switched capacitor system and a permanent magnet synchronous machine (PMSM). The sizing of the converter and the machine are considered strongly dependent due to the series quasi-resonant topology. The system modelling is based on a semi-analytical approach validated by finite element (FE) simulations. It involves an analytical modelling of the electrical machine and a numerical time solving of the electrical circuit sub-model because of the natural switching events of diodes. The optimization is carried out by SQP (Sequential Quadratic Programming). The model gradients are computed combining mathematical laws, symbolic derivation and automatic differentiation. Finally, trade-offs and gains on the machine power density, the magnet volume and the efficiency are investigated through a Pareto approach.

We study the relation between the induced anisotropy obtained on nanocrystalline Fe 73.0 Cu 1.1 Nb 3.1 Si 15.7 B 7.1 toroidal cores crystallized under transverse field at 570 °C, and the polarization J c of nanograins. To do this, an original disposition is used, mixing treated cores with cores made of electrotechnical SiFe alloy, featuring same geometry, using the interfacial magnetic charges to increase the field in treated cores. The field supplied by the coil being μ 0 H a = 33 m T , playing on the proportion between treated and SiFe cores, effective field ranging between 33 m T and 230 m T were obtained inside treated cores. As a result, the induced anisotropy at the scale of the alloys at the end of crystallization range from K u = 12 J / m 3 to K u = 20 J / m 3 . To simulate the evolution of J c during the crystallization process, the configuration of treated and SiFe cores in the sample holder was implemented in Altair FluxT FEM simulation environment with the dedicated polarization laws. Dealing with treated cores, the law J cor ( H ) at the scale of the core reflects the law J c H featured by nanograins during the crystallization process. J c H was modelized as a function of the crystallized fraction f c . The relation between the simulated J c and the experimental final values of K u / f c (i.e. the anisotropy in nanograins) was then studied. This was done considering the polarization 〈 J c 〉 averaged on the entire crystallization process, wondering about a possible memory effect.

This paper investigates the effect of the cobalt addition on the magneto-crystalline anisotropy parameter of some polycrystalline ferrites. Magnetization curves have been experimentally determined at different temperatures on Ni1−xZnxFe2O4 sintered samples with or without cobalt addition. In each case, a law of approach to saturation has been fitted to the measured data in order to extract the anisotropy parameter K1 representative for the polycrystalline material. Besides, measurement of the complex susceptibility and power core-loss up to 5 MHz has been performed. This approach allows a discussion on the role of cobalt addition on the power core-loss mitigation. It has been found that the substitution with 0.02 mol. of Co leads to a small decrease in the K1 values. This evolution is consistent with the rise in the rotational permeability. However, the change in K1 cannot account for the core-loss reduction with Co. Rather, it is confirmed that Co hinders the domain wall displacement and subsequent dissipation up to an induction level that depends on the grain size.

WOS:000458776900018

This article focuses on the modeling of the hysteresis loop featured by Fe-Cu-Nb-Si-B nanocrystalline alloys with transverse induced anisotropy. The magnetization reversal process of a magnetic correlated volume (CV), characterized by the induced anisotropy Ku, and a deviation of the local easy magnetization direction featuring the effect of a local incoherent anisotropy Ki, is analyzed, taking account of magnetostatic interactions. Solving the equations shows that considering a unique typical kind of CV does not enable accounting for both the domain pattern and the coercivity. Actually, the classical majority CVs obeying the random anisotropy model explains well the domain pattern but considering another kind of CVs, minority, mingled with classical ones, featuring a magnitude of Ki comparable to Ku, is necessary to account for coercivity. The model has been successfully compared with experimental data.

This paper focuses on the modeling of the hysteresis of Fe–Cu–Nb–Si–B nanocrystalline alloys with transverse induced anisotropy $K_{u}$ based on the behavior of a correlated volume (CV). Only coherent rotation mechanism was considered, given the chosen value of $K_{u}$ . The formulations account for $K_{u}$ , the incoherent anisotropy $K_{i}$ , and the magnetostatic energy. The solving of the equations shows the existence of two kinds of CVs: the first one is responsible for the domain pattern, while the other causes the coercivity. The model has been compared with experimental data, and improved by considering the existence of a minority of CVs featuring strong incoherent anisotropy, causing the coercivity, mingled with classical CVs obeying the random anisotropy model.

International audience; At high temperature, FeSi nanograins obtained after partial crystallization of amorphous Fe-Si-Cu-Nb-B precursor are magnetically decoupled and superparamagnetic, due to the disappearance of the magnetism of the residual amorphous matrix. At a transition temperature Ttr typically ranging between 600 K and 850 K, still above the amorphous Curie temperature, a spontaneous polarisation JSsf appears, despite a much lower blocking temperature. Magnetostatic interactions, rendered by the Lorentz field (L.f.), or a residual ferromagnetic coupling between grains through the amorphous medium, have been invoked to explain this behavior. We investigate here the magnetostatic hypothesis. An improvement of the L.f. model is carried out, based on the idea that the field acting on a nanograin is screened by a surrounding soft shell. The permeability of this shell in the vicinity of Ttr is determined, leading to an attenuation factor S = 2.8 and a decrease of Ttr compared to the L.f. approximation. Moreover, a description of the spontaneous magnetization curve JSsf(T) / JS(T) is obtained, with a slope near Ttr much sharper than predicted by the (Ttr - T)1/2 law associated to an invariant molecular field factor. Comparison with experiments shows good agreement.

In the design of power electronic converters, the choice of the suitable magnetic alloys and the measurement of the variations of their magnetic properties versus the temperature are fundamental issues. A theoretical model based on Neel theory and that takes into account wall displacement and coherent rotation was elaborated to derive the expression of the complex permeability versus the frequency. The static and the dynamic behavior are considered. The dependence of temperature is implicit in this model, i.e. the parameters involved in the expression of the complex permeability may depend on the temperature. An impedance analyzer has been used to measure the open circuit and short circuit complex impedances of a toroidal core versus the frequency at several temperatures ranging from 20°C to 180°C. The complex permeability of the material is then deduced. Finally, the theoretical model is used to identify the domain susceptibility and the anisotropy energy of the materials. The effect of temperature on these parameters is analyzed. The result obtained are valuable for the design of a power electronic converters from the magnetic and thermal viewpoints. The results prove the need for the combination of heat transfer and magnetic mechanisms at the design.

Behaviour of the Nanocrystalline multilayer cores are investigated by use of a 1D electromagnetic propagation model. The magnetic properties of conductive ferromagnetic materials are considered using a domain-wall magnetization model. The physical parameters of the model are domain's width, d, and the initial susceptibility χ 0 . Numerical solutions of the problem taken up with impedance measurements are used to correlate d and χ 0 to macroscopic behaviour of the material.

International audience; The decrease of coercive magnetic field strength according to applied mechanical stress at audible and inaudible frequencies is investigated. To this aim, an experimental setup is introduced to both measure mechanical and magnetic behaviors. The mechanical resonant modes of a magnetic ring core sample are tracked to allow large longitudinal bendings and to reduce significantly the hysteresis loop width. Results are then set forth to show that elastic mechanical applied stress is relevant to describe the reduction of coercive field strength measured for both steady and transient states.

International audience; Ultrasoft magnetic materials, such as amorphous, nanocrystalline, and polycrystalline alloys, have been successfully used for power electronic applications during recent years. However, enhancements are needed for the integration of power electronic features, which involves high power densities and operating frequencies up to a few megahertz. Complex permeability spectra, which are used to describe material behavior in these applications, depend mainly on domain-wall motions and coherent magnetization rotation mechanisms. In this paper, we present a model describing these mechanisms, in terms of magnetic anisotropies and domain structure of the material. To validate the model, we measured permeability spectra of polycrystalline Ni-Fe alloys under mechanical stress using a specific setup. These measurements are suitable for comparing the physical model according to different magnetoelastic anisotropies. Results are useful for correlating high-frequency magnetic behavior and the annealing process of materials.