Research On Magnetic-Thermal Coupling And Cooling Of Switched Reluctance Motor Of Electric Vehicle

With the increasing depletion of petroleum resources,environmental pollution and national policies,new energy vehicles have developed rapidly.As the core component of new energy vehicles,the motor provide sufficient power output for automobiles.Switched reluctance motor(SRM)is used in new energy vehicles because of its small size,simple structure,wide speed range and low cost.Because the motor will generate a lot of heat due to the power loss during operation,which will affect the performance of the motor and reduce its service life,it is very necessary to study the temperature rise and cooling of the motor.This paper firstly describes the structure and working principle of the 3-phase 12/8pole switched reluctance motor,and introduces the mathematical model of the motor and the heat transfer theory of the motor.Using Ansoft Maxwell software to analyze the magnetic field of the switched reluctance motor,the distribution of magnetic field lines and magnetic density cloud maps of the motor at different positions are obtained.The yoke and tooth core magnetic density waveforms and changes of the motor stator and rotor are analyzed,and the Fourier decomposition is carried out.Using the harmonic analysis method to calculate the core loss of the motor,and the values of the motor winding loss,mechanical loss,and stray loss are obtained according to the formula.Then,the equivalent calculation of each part of the motor is carried out to determine the equivalent thermal conductivity of the stator rotor core,stator slot and air gap between the stator and rotor,and the convective heat transfer coefficient of each surface of the motor is calculated.Then,Ansys Workbench finite element software was used to establish the thermal model of switched reluctance motor,the loss value of the motor was mapped to the temperature field,and the magnetic-thermal coupling analysis was carried out to obtain the temperature rise of the motor stator,rotor and windings.Then the orthogonal test was designed by taking into account the three factors affecting the number of cooling channels,the shape of section and the layout Angle of inlet and outlet.Finally,according to the temperature rise of the motor,the cooling structure of the motor is designed using the 3D modeling software Catia.The effects of the number of cooling channels,the cross-sectional shape and the arrangement angle of inlet and outlet ports on the maximum temperature of the motor and the pressure drop of the pipe flow were studied using Fluent finite element software.The results show that with the increase of the number of cooling channels,the maximum temperature of the motor decreases gradually,and the pressure difference of inlet and outlet increases gradually.Reasonable design of cooling channel section shape can improve the heat dissipation performance of the motor and reduce the pressure drop of the pipe flow.When the layout Angle of inlet and outlet pipe and housing changes from vertical to tangent,the maximum temperature of the motor is basically unchanged,but the pressure difference between inlet and outlet is getting lower and lower.Then the orthogonal test is designed to optimize the cooling channel structure by considering the number of cooling channels,the shape of section and the Angle of inlet and outlet.According to the simulation results,the optimal parameter combination for the heat dissipation of the motor and the pressure drop of the tube flow is obtained by using the comprehensive equilibrium method.