Modeling Of Magnetic Properties Of Electrical Steel Laminations Considering Effect Of Manufacturing And Its Application

Building the resource-saving society has reached a consensus worldwide.Efficient and energy-saving motors have been vigorously developed in new energy vehicles.In the future,the drive motor will develop towards the trend of high speed,high frequency and high service temperature to improve the power density.Manufacturing process has a significant impact on the magnetic and safety performance of the motor,which easily leads to insufficient joint strength and excessive iron loss resulting in structural damage and low motor efficiency,respectively.Therefore,studying the influence of the manufacturing process on magnetic and safety performance is conducive to improving motor performance and enhancing the competitiveness of the industry.The manufacturing process of the stator core mainly includes punching,welding,pressing and so on.Residual stress,plastic strain and inter-conduction introduced by the manufacturing process greatly increase the iron loss of the motor stator.Manufacturing process of the stator core faces the dual technical challenges of magnetic and safety performance.High welding power can obtain electrical steel laminations with high tensile force,which usually leads to excessive iron loss.Low welding power can meet the requirements of motor efficiency,which often makes low tensile force.The pulsed laser welding only illuminating at the material interface is adopted to reduce the iron loss of the stator core while ensuring sufficient tensile force simultaneously,which has a broad application prospect in the connection of electrical steel.At present,the pulsed laser welding of stator core lacks the weld lobe with iron loss and tensile force as the evaluation indexes,which is used to guide the application of pulsed laser welding in the connection of electrical steel.During determining the right boundary of weld lobe,the prediction of hysteresis loss and eddy current loss does not comprehensively consider the effect of residual stress,plastic strain,inter-conduction and uneven distribution of eddy current density,which results in inaccurate prediction of iron loss of laminations after welding.During determining the left boundary of weld lobe,the influence of process parameters of pulsed laser welding on the tensile force of welded laminations is unknown and the suitable prediction model is missing,which results in inaccurate prediction of tensile force of welded laminations.Methods of experimental investigation,finite element analysis and mathematical modeling are used in this paper.The method for determining the weld lobe of pulsed laser welding of the stator core is proposed with tensile force and iron loss as evaluation indicators.In order to accurately predict the iron loss of welded electrical steel laminations,a hysteresis model of electrical steel considering the effects of residual stress and plastic strain is established.And an eddy current loss model of electrical steel laminations considering the local connectivity and edge effects is also established.Through the above two models,the right boundary of the weld lobe of pulsed laser welding is determined.In order to accurately predict the tensile force of welded electrical steel laminations,a "step fitting method" is used to establish the prediction model of tensile force of electrical steel laminations after pulsed laser welding.Through the tensile force model,the left boundary of the weld lobe of pulsed laser welding is determined.Finally,the weld lobe of pulsed laser welding of the stator core is established to guide the application of the pulsed laser welding in the connection of electrical steel.The main content of the full text is as follows:(1)Hysteresis model of electrical steel with residual stress and plastic strainIn this paper,the effect of residual stress and plastic strain on hysteresis characteristics is explained based on the equilibrium conditions of domain wall movement.A modified hysteresis model of electrical steel with residual stress and plastic strain is established based on the classical hysteresis model introducing dislocation influence term.The subsequent magnetic properties tests of electrical steel with residual stress and plastic strain are carried out and a model parameter identification program is designed to identify the model parameters.Model parameters at different residual stresses and plastic strains have been given in this paper.Finally,verification experiments are carried out to verify the accuracy of hysteresis model.Compared with the traditional hysteresis model,the accuracy of hysteresis model established in this paper is improved by about 12%.(2)Eddy current loss model of electrical steel laminations with multiple loops and inter-conductionIn this paper,changes in eddy current characteristics of electrical steel laminations are analyzed.The eddy current path changes due to inter-conduction.Skin effect and Edge effect lead to uneven distribution of eddy current density.Residual stress after welding causes the relative permeability of the material to change.Through the above analysis,an eddy current loss model of electrical steel laminations with multiple loops and inter-conduction is established.Ratio of the maximum eddy current density in junction area of laminations to that in unwelded area is defined as the edge effect coefficient,which is used to reflect the edge effect of eddy current.Ansoft Maxwell 3D software is used to determine edge effect coefficients at different weld depths.Finally,the accuracy of the eddy current loss model is verified by magnetic property tests of electrical steel laminations at different frequencies.(3)Experimental study on pulsed laser welding of electrical steel laminationsIn this paper,a test platform for pulsed laser welding of electric steel laminations and electromagnetic performance test platform are built.Rectangular laminations are designed to study the tensile force of welded laminations.For non-oriented electrical steel B27AHV1500,the microstructure of pulsed laser weld and magnetic properties of welded laminations are analyzed.A "step fitting method" is used to establish the prediction model of tensile force of electrical steel laminations based on pulsed laser welding experiments,which can reflect the influence of peak power and duty cycle on the tensile force of welded laminations.Through the model established in this paper,the tensile force of electrical steel laminations after pulsed laser welding can be accurately predicted.(4)Verification of magnetic properties and weld lobe of pulsed laser welding of the stator coreIn this paper,weld lobe of pulsed laser welding of the stator core is proposed.tensile force and iron loss are used as evaluation indicators for weld lobe.Based on the tensile force model established in this paper,the left boundary of the weld lobe is determined.Using the hysteresis model and eddy current loss model established in this paper,iron loss of the stator core after welding is predicted and the right boundary of the weld lobe is determined.Finally,the accuracy of weld lobe is verified by experiments to provide guidance for the application of the pulsed laser welding in connection of electrical steel.In summary,the influence of manufacturing on magnetic and safety performance of electrical steel laminations is systematically studied in this paper.Iron loss and tensile force of electrical steel laminations can be accurately predicted by models established in this paper.The method to determine the weld lobe of pulsed laser welding of stator core is proposed.Our work provides guidance for the application of the pulsed laser welding in connection of electrical steel.