Research On Magnetic Properties Model Based On Domain Energy Minimization Principle Under Harmonic Magnetic Field

The wide use of frequency converters and nonlinear loads causes the presence of harmonic components of magnetic field of the electrical machine core,which will change the magnetic properties,magnetostrictive properties and loss properties of the core material.These properties are of great significance for the optimal design of high power density motors.The accurate description of core material properties under harmonic magnetization requires the establishment of appropriate hysteresis or magnetostrictive models.Currently,the hysteresis models studied by domestic and foreign scholars can be divided into microscopic,mesoscopic and macroscopic scales.The long calculation time of microscopic scale model is not suitable for calculating the magnetic properties of electrical steel sheets.Traditional hysteresis models at the macroscopic scale lack detailed description of the physical magnetization theory,and the accuracy of hysteresis properties is limited under actual working conditions.In recent years,some foreign scholars have proposed a multiscale energy model,which combines mesoscopic scale magnetic domain magnetization mechanism with macroscopic scale magnetic properties.With the support of the National Natural Science Foundation of China,a multiscale magnetic domain energy model under harmonic magnetization was established based on the mesoscopic scale magnetic domain free energy.This model not only took the magnetic field into account,but also was coupled with the effect of mechanical force field on the magnetic properties of the material.The minimum value of total energy density function of magnetic domains was determined by the magnetization state of magnetic domains.Then a series of hysteresis loops(including local hysteresis loops)under the harmonic magnetic fields were simulated according to the average principle.The hysteresis model was applied to the analysis of magnetic properties of an asynchronous motor core,and a new attempt was made for precise simulation of magnetic properties of magnetic materials used in electrical equipments under actual working conditions.The main research contents of the thesis are as follows:Firstly,a multiscale magnetic domain energy model was established based on the five kinds of magnetic domains free energy.The magnetic domain energy formulas were optimized according to the structure and definition of the model.At the same time,to consider the hysteresis effect of electrical steel sheets under harmonic magnetization,the pinning energy was introduced.The stop operator was employed to simulate the pinning effect.Moreover,the magnetic properties of non-oriented silicon steel sheets under different high harmonic magnetic fields were measured and analyzed by the existing experimental equipment in the laboratory.Secondly,the multiscale magnetic domain energy model parameters were identified based on the experimental data.The magnetization vector directions and volume fractions of magnetic domains were determined by calculating the local minimum energy by genetic algorithm to obtain macroscopic hysteresis properties.The simulation results of the model were compared with measurement results to verify the effectiveness of the multiscale energy model.The difference between the magnetic and loss properties of non-oriented silicon steel sheets was simulated by two magnetic domains model and six magnetic domains model,respectively.Then the influence of volume fraction calculated by Boltzmann formula on the speed and accuracy of the model result was verified.Finally,the hysteresis model mentioned above was applied to the simulation of magnetic performance of an asynchronous motor core.ANSYS software was used to simulate the magnetic field of an asynchronous motor.The input excitation contained harmonic components.According to the simulation results,the magnetic field intensity of one time period at any node of the motor was obtained,and the hysteresis properties of the core could be calculated by substituting magnetic field intensity into the multiscale energy model.It lays a foundation for the research of using the hysteresis model to solve practical engineering problems.