Magnetic dipole collectives for modelling the ferromagnetic material characteristics in electrical machines

点击翻译按钮获取中文摘要

Modern numerical electromagnetic field computation of electrical machines uses the magnetization curve to describe the nonlinear ferromagnetic material characteristics of the iron parts. The mean magnetization curves are obtained by measurements taken from a ring specimen tester or an Epstein frame. The scientific literature provides different hysteresis models which are either based on mathematical or physical equations or which are of phenomenological nature. Common models are e.g. the Preisach model, the Jiles-Atherton model and the Landau-Lifshitz model. The first two of them describe the macroscopic, transient behaviour of the magnetization dependent on the external magnetic field intensity as ordinary differential equations. However, both of these models neglect the local magnetic field distribution within the active iron parts of the machine.However, the Landau-Lifshitz model describes the microscopic behaviour of ferromagnetic materials. Based on different interactions, the alinement of elementary dipoles (magnetization vectors) is optimized mathematically to minimize the total free energy of the system. The interactions can be derived from physical relations that are based on the crystal structure and the texture of the material at the atomic scale.The model investigated in detail in this project abstracts the physical relations provided by the Landau-Lifshitz model and transfers them to a macroscopic grid. Therefore, comprehensive preliminary studies with two- and three-dimensional collectives of magnetic dipoles were performed. The results obtained in this studies show a qualitative good agreement between simulated and measured values. The dipoles within the collective of the presented model interact according to the stray-, exchange and anisotropy field, as it they are formulated in the Landau-Lifshitz-Model.Because of the above-mentioned abstraction of the Landau-Lifshitz-Model the physical relationship of the parameter set, which belongs to the model under investigation, is lost for the moment. In order to rebuild this relationship, first it is necessary to develop a standardized parameter identification process that is, as far as possible, guided by physical observations on the sample and the different excitation conditions. In a second step, from the found qualitative relationships, quantitative connections between the parameter set and the measured hysteresis behaviour will be deduced.Summing up, the aim of this project is a comprehensive investigation of the introduced dipole model in term of its abilities of imitating and predicting quantitatively the hysteresis behaviour of macroscopic structures considering different external influences on the material sample.