| Power transformers,motors and other modern electrical equipment operating under the action of a variety of excitation sources in its internal and surrounding will produce a variety of physical field coupling effects,their fine design and high-precision performance analysis often involves electric,magnetic,thermal,force and other multi-physical field coupling problems.Electrical materials such as conductive materials,magnetic materials and insulating materials are widely used in electrical equipment.The electromagnetic characteristics of these materials depend on the coupling of various physical fields.For example,magnetic materials produce hysteresis and eddy current loss under the action of alternating magnetic field,and current produces Joule heat loss in the conductor,these losses will lead to the rise of motor temperature in the form of heat source during the operation of electrical equipment,in turn,excessive temperature rise will affect the performance of various materials in the motor,at the same time,the change of material performance will react on multi-physical field.Therefore,considering the interdependence of electromagnetic characteristics of electrical materials in the multiphysical field coupling analysis of electrical equipment is a necessary condition to improve the design quality and performance analysis accuracy.This thesis focuses on the influence of the complex magnetic characteristics of electrical magnetic materials on the multi-physical field coupling analysis of electrical equipment.Through the measuring devices,the loss characteristics of electrical steel sheet under the action of multiple physical factors such as temperature and stress and the demagnetization characteristics of permanent magnet at high temperature are measured,and the corresponding mathematical models are established.In order to verify the positive effect of the complex magnetic characteristics of coupled magnetic materials on the accurate analysis of multiple physical fields of electrical equipment,the iterative coupling analysis of electromagnetic field,temperature field,fluid field and stress field of a high-speed permanent magnet motor is performed,the comparison of the results shows the necessity of considering the complex electromagnetic characteristics of electrical materials.Firstly,the magnetization curves and iron loss curves of non oriented electrical steel B35A230 under different frequencies,stresses and ambient temperatures were measured on the experimental platform.By comparing the magnetization curves and iron loss curve data under different measurement conditions,the influence law of stress and temperature on the permeability and loss of electrical steel sheet is clarified,and the core loss term mainly affected by the change of different physical factors is determined.Based on the classical iron loss calculation model,a motor core loss model considering the effects of frequency,stress and temperature is established.It provides data support for the comparison and application of the classical iron loss calculation model,the improved model considering the influence of multiphysical factors,and the iron loss calculation of motor in the magnetic thermal bi-directional coupling analysis.Then,on the premise of clarifying the degradation mechanism of permanent magnet,taking the surface magnetism of permanent magnet as the characterization parameter of permanent magnet magnetic properties,the degradation experiments of permanent magnet at different temperatures are carried out,and the logarithmic function model is selected to model the degradation of permanent magnet.The model is used to calculate the demagnetization rate of permanent magnet N45 UH at the working temperature of 100 ℃,and the demagnetization law of permanent magnet at this temperature under the model is analyzed.The changes of the whole magnetic properties after several times are obtained.Finally,the complex magnetic characteristics of magnetic materials and multi-physical field coupling analysis method are applied to the calculation of temperature field and stress field of a 132 k W high-speed permanent magnet motor.The coupling effect of electromagnetic characteristics of conductive materials and magnetic materials is fully considered,and compared with the analysis results without coupling effect.Verify the effectiveness of the analysis method in this thesis. |
