F. Fiorillo

An improved approach to power losses in magnetic laminations under nonsinusoidal induction waveform

It is shown that it is possible to accurately predict power losses in ferromagnetic laminations under nonsinusoidal magnetic flux by specifically considering the dependence of hysteresis, classical, and excess loss components (P/sub h/, P/sub c/, and P/sub e/, respectively) on the magnetic induction derivative B. Basically, it is assumed, through generalization of experimental and theoretical results under sinusoidal induction, that P/sub h/ is proportional to the average value of the instantaneous induction derivative, P/sub c/ is proportional to the average value of the square of the instantaneous induction derivative, and P/sub e/ is proportional to the average value of the instantaneous induction derivative to the three-halves power. An analytical expression for total power losses under distorted flux is consequently worked out. Experiments are reported concerning grain-oriented, nonoriented, and amorphous laminations, with distortion introduced by a variable amount of the third harmonic flux component. >

One-dimensional/two-dimensional loss measurements up to high inductions

A thermometric-fieldmetric method has been developed by which Fe–Si laminations are characterized under either alternating or rotational excitation up to peak induction Bp=1.85 T in the frequency range 2 Hz≤f≤200 Hz. The measurement is performed on circular samples (diameter=140 mm) under digitally controlled one-dimensional/two-dimensional flux loci. The power losses at high inductions are determined by measurement of the rate of rise of the specimen temperature. Imperfect adiabatic behavior of the material is accounted for by physical modeling of the thermal diffusion process. The low-to-medium induction range, up to Bp∼1.7 T, is covered by conventional fieldmetric measurements, which, in conjunction with the thermometric approach, permit one to achieve a complete characterization of the magnetic sheets versus Bp and f.

Core loss prediction combining physical models with numerical field analysis

Abstract An improved procedure for calculating iron losses in electrical machine cores is presented. It is based on physical models and experiments on losses in magnetic laminations, under one- and two-dimensional fields, and exploits a finite element computation of the flux distribution in the core. Physical modelling relies on the basic concept of loss separation, extended to the case of vectorial magnetic flux with generic elliptical loci. Starting from a theoretical formulation of power losses under unidirectional fields and generic induction waveform and its extension to the case of elliptical flux, general expressions are derived for the hysteresis, excess and classical loss components in two dimensions. Quasi-static and 50 Hz total losses under alternating sinusoidal flux and pure rotational flux are the sole experimental data needed for a complete loss prediction. In the present work, two different types of nonoriented FeSi 3.2% laminations are considered, which are assumed to be assembled into a model three-phase motor core. By means of a 2D finite element analysis, the distribution of magnetic field and induction in the core is obtained for different values of the supply current and the loss calculation is carried out. A comparison with standard loss calculation methods points to the detrimental role of two-dimensional fluxes, although this may not be fully appreciated in conventional 50 Hz induction motors.

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.

Loss measurements on amorphous alloys under sinusoidal and distorted induction waveform using a digital feedback technique

A newly developed digital feedback wattmeter, allowing power loss measurements in soft laminations under generic induction waveform is presented. The system is intrinsically free of auto‐oscillations, typical drawback of analog feedback circuits, and can therefore be operated in a wide frequency range (0.5 Hz–100 kHz). Loss measurements performed by this setup under sinusoidal and distorted induction waveforms on Co based amorphous ribbons are reported. It is shown that the classical approximation to the prediction of power losses under distorted induction largely fails to account for the experimental results. A novel theoretical approach, based on the statistical theory of losses, is discussed and successfully applied to the experiments. In particular, it is shown that knowledge of the loss components under sinusoidal induction at a given magnetizing frequency permits one to make an accurate prediction of the effect of distortion at that frequency as well as other ones. Illustrative applications at 1 kHz...

Loss separation in soft magnetic composites

We report and discuss significant results on the magnetic losses and their frequency dependence in soft magnetic composites. Two types of bonded Fe-based materials have been characterized at different inductions from dc to 10 kHz and analyzed by extending the concept of loss separation and the related statistical theory to the case of heterogeneous materials. Starting from the experimental evidence of eddy current confinement inside the individual particles, the classical loss component is calculated for given particle size distribution. Taking then into account the contribution of the experimentally determined quasistatic (hysteresis) loss, the excess loss component is obtained and quantitatively assessed. Its behavior shows that the dynamic homogenization of the magnetization process with frequency, a landmark feature of magnetic laminations, is restrained in these materials. This results into a partial offset of the loss advantage offered by the eddy current confinement.

Advances in FeSi properties and their interpretation

Abstract Recent progress in the preparation and magnetic properties understanding of improved FeSi laminations is shortly reviewed. Attention is devoted, in particular, to methods leading to decreased energy losses, either by means of improved structural properties or high Si content (up to 6.5 wt%). It is put in evidence that the physical modelling of losses, besides providing a rationale for the improvement of the material properties, can lead to very general predictions, where the lamination performances under complex regimes, as found in many devices, can be correctly described.

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.

Computation of Eddy Current Losses in Soft Magnetic Composites

We compute the classical eddy current losses in soft magnetic composite (SMC) materials, taking into account the eddy current paths appearing at the scale of the sample cross-section because of random contacts between the grains. The prediction of this loss contribution is a challenging task, because of the stochastic nature of the associated conduction process. We start our study from an identification of the statistical properties of the contacts between grains, starting from resistivity measurements. We then develop a numerical loss model for random grain-to-grain conduction, by which we demonstrate that the classical loss in SMCs can be decomposed into a contribution deriving from the eddy currents circulating inside the grains and a contribution due to the macroscopic eddy currents flowing from grain to grain via random contacts. An experimental validation of this model is proposed for a representative SMC material, where the magnetic losses are measured in ring samples with a range of cross-sectional areas.

Loss and Permeability Dependence on Temperature in Soft Ferrites

Wideband energy loss and permeability behavior of Mn-Zn and Ni-Zn ferrite ring cores has been investigated between 2 and 50 mT up to 140degC. The measurements have been performed by a fluxmetric method from direct current (dc) to 10 MHz and by a transmission line method from a few 105 Hz to 1 GHz. While magnetic softening upon heating from room temperature always occurs at low frequencies, mixed behavior is observed, depending on the polarization value, on approaching the megahertz range. The loss versus frequency curves at different temperatures tend to coalesce towards the microwave regime. The overall loss and permeability properties are interpreted recognizing the separate roles of domain wall (DW) and rotational processes and their frequency dependence. Weakening of the magnetocrystalline anisotropy with temperature leads to reduced DW dissipation, while affecting the spectral distribution of the damped spin precessional frequencies. Eddy current mechanisms are not involved in such phenomena. Dissipation effects by DWs and rotations are prevalent in the lower and upper range of frequencies, respectively. This feature is quantitatively interpreted generalizing concepts and methods of the statistical theory of losses.