Anisotropy of losses in grain-oriented Fe-Si

Comprehensive assessment of the magnetic behavior of grain-oriented steel (GO) Fe-Si sheets, going beyond the conventional characterization at power frequencies along the rolling direction (RD), can be the source of much needed information for the optimal design of transformers and efficient rotating machines. However, the quasi-monocrystal character of the material is conducive, besides an obviously strong anisotropic response, to a dependence of the measured properties on the sample geometry whenever the field is applied along a direction different from the rolling and the transverse (TD) directions. In this work, we show that the energy losses, measured from 1 to 300 Hz on GO sheets cut along directions ranging from 0° to 90° with respect to RD, can be interpreted in terms of linear composition of the same quantities measured along RD and TD. This feature, which applies to both the DC and AC properties, resides on the sample geometry-independent character of the RD and TD magnetization and on the loss separation principle. This amounts to state that, as substantiated by magneto-optical observations, the very same domain wall mechanisms making the magnetization to evolve in the RD and TD sheets, respectively, independently combine and operate in due proportions in all the other cases. By relying on these concepts, which overcome the limitations inherent to the semi-empirical models of the literature, we can consistently describe the magnetic losses as a function of cutting angle and stacking fashion of GO strips at different peak polarization levels and different frequencies

Wideband magnetic losses and their interpretation in HGO steel sheets

The magnetic properties of high-permeability grain-oriented (HGO) Fe-Si sheets have been investigated in the frequency range 1 Hz-10 kHz, with attention devoted to the role of thickness on the behavior of the magnetic losses and the phenomenology of skin effect. The study is focused on the wideband response of 0.174 mm and 0.289 mm thick sheets, comparatively tested at peak polarization values ranging between 0.25 T and 1.7 T. The experiments associate fluxmetric measurements with direct Kerr observations of the dynamics of the domain walls. A picture of the magnetization process comes to light, where the dynamics of the flux reversal takes hold under increasing frequencies through the motion of increasingly bowed 180 degrees walls, eventually merging at the sheet surface for a fraction of the semi-period. This effect can be consistently predicted, starting from the Kerrbased knowledge of the equilibrium wall spacing, by the numerical modeling of the motion of an extended array of 180 degrees domain walls, subjected to the balanced action of the applied and eddy current fields, and the elastic reaction of the bowed walls. This model can be incorporated into the general concept of loss separation, by calculating the classical loss component through the solution of the Maxwell's diffusion equation under a magnetic constitutive law identified with the normal DC curve. The numerical domain wall model and the loss decomposition consistently predict that the excess loss component, playing a major role in these grain-oriented materials at power frequencies, tends to disappear in the upper induction-frequency corner

Loss Prediction in DC-Biased Magnetic Sheets

Power losses in soft magnetic materials can be solidly assessed by the statistical theory of losses (STLs), which provides physical foundation to the concept of loss separation. The theory is, however, limited to the conventional case of symmetric hysteresis loops and cannot be straightforwardly applied for a magnetic core operating under a dc bias. We show, in this paper, that such constraint can be released by combining the STL with a simplified approach to the dynamic Preisach model. This approach leads to the more affordable static Preisach model with largely reduced computation time. In this way, the hysteresis and excess loss components, with and without dc bias, are identified and calculated starting from a minimum set of experimental data. We provide a wide-ranging experimental validation of the theory, which is applied to the behavior of the energy loss versus frequency, measured up to f = 1 kHz, in non-oriented and grain-oriented iron-silicon sheets and in iron-cobalt alloys, subject to different polarization bias levels

Modeling of saturable inductors for application in DC-DC converters

This paper deals with a method by which the experimental characterization of a power inductor is obtained from onboard measurements that exploits a low-cost DC-DC buck converter to supply the inductor under test with quasi-rectangular voltage waveforms of different amplitudes and bias conditions. The measurements of the voltage vL(t) across the inductor and the current iL(t) are performed up to inductions approaching the magnetic saturation. After suitable integration of vL(t), the magnetic flux is obtained as a function of iL and the accuracy of the described identification process is checked by comparing the measured waveform of the current to numerical simulation of the same quantity obtained assuming as input the DC current component and the measured voltage waveform

Global Quantities Computation Using Mesh-Based Generated Reluctance Networks

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