Experimental and Theoretical Analysis of Soft Magnetic Materials for Power applications

The efficiency of electrical machines carries a global impact because they fulfill about three-quarters of global electrical energy consumption. Its improvement requires a sound knowledge of energy loss properties of magnetic materials used in the core of electrical machines, especially non-conventional supply conditions, such as non-sinusoidal, high induction, alternating (1-D) and rotating (2-D) flux waveforms that have been posed with the incorporation of new electronic devices and materials in the systems. For these reasons, novel theoretical models and experimental techniques need to be developed to obtain the loss behavior under these complex flux regimes. To address these issues, experimental investigation and theoretical analysis have been carried out in this thesis on different magnetic materials and a wide ensemble of supply conditions. The aim of the theoretical analysis was to fill the gap between the physicists and the engineers by developing simple models that can be applied to compute the loss under realistic supply conditions. This theoretical frame is rooted in the physical principle of the separation of loss and the Statistical Theory of Loss (STL) by which the loss can be separated into the hysteresis, classical, and excess components. The concept of loss separation has been exploited under 1-D flux and extended to 2-D fluxes, where the relations between alternating and rotational losses have been obtained on a number of different materials, this analysis restricted to the region not influenced by skin effect. The proposed theoretical models have been tested by comparing loss figure of different magnetic materials over a wide range of frequencies, induction levels, and conventional or non-conventional supply conditions. To this purpose, loss characterization of non-oriented Fe-(3.2wt \%)Si steels have been performed using a three phase magnetizer able to generate 1-D and 2-D flux patterns, up to saturation magnetization. Fieldmetric and Thermometric methods have been applied at low and very high induction levels. Loss characterization of other non-oriented Fe-Si and low carbon steels have also been performed under 1-D flux at very low and high sinusoidal inductions using Epstein frame, single sheet tester or ring samples, over frequencies ranging from quasi-static conditions up to 10 kHz. Systematic uncertainties have been observed in measurements using a Single Sheet Tester due to MMF drop in flux closing yoke and a compensated Permeameter has been designed to reduce these uncertainties by compensating the MMF drop in the flux closing yoke.