Research On Temperature Rise And Control Of High Power Density Permanent Magnet Synchronous Motor For Electric Vehicles

China’s new energy automobile industry has developed rapidly.As one of the core components of electric vehicles,the driving motor has great research significance,among which high power density permanent magnet synchronous motor(PMSM),which is the development trend of motor for electric vehicles,has many characteristics,such as high power,small size and wide speed range.However,these characteristics also bring problems such as high heat flux density and poor heat dissipation conditions.Therefore,it is necessary to study the temperature field of motors,demagnetization characteristics of permanent magnets and related current vector control theory.In this paper,the high power density flat wire winding permanent magnet synchronous motor is taken as the research object.Firstly,the temperature field of permanent magnet synchronous motor is analyzed,then the vector control strategy based on control current MAP is developed,and then the permanent magnet temperature observer is built based on thermal network method.Finally,the high temperature permanent magnet protection strategy is developed and the effectiveness of the proposed strategy is verified by the simulation conducted on Matlab/Simulink.The main research contents of this paper are as follows:(1)Simulation and analysis of motor temperature field based on computer fluid dynamics.Based on the simulation requirements of computer fluid dynamics(CFD),the simplified three-dimensional model of the motor is established in Solidworks,and each component in the motor model is meshed in ANSYS Meshing.The loss of the motor and influencing factors are analyzed,and solve the loss of the nominal working condition and peak working condition of the motor.In order to simulate the actual running state of the motor,according to the structural characteristics of the motor and considering the influence of turbulent air at the end,the simulation boundary conditions inside the motor are solved,and the heat exchange coefficient of each heat transfer surface is defined.Using ANSYS Fluent software,the steady-state temperature rise simulation and transient temperature rise simulation of the motor are carried out.The axial and radial temperature distribution characteristics of the motor are analyzed,which verifies that the temperature rise meets the requirements of carrying in vehicles.At the same time,it provides a reference for the construction of thermal network model and the verification of motor high temperature protection strategy.(2)Vector control strategy of permanent magnet synchronous motor based on control current MAP.Based on the analysis of the maximum torque per ampere(MTPA)control,maximum torque per voltage(MTPV)control and constant torque field weakening control,the optimal control current of each control methods is solved.An acquisition algorithm is proposed to obtain the vector current control MAP of the permanent magnet synchronous motor.In order to improve the torque control accuracy of vector control strategy,the current loop feedforward control is applied in the strategy,the current MAP is solved considering the influence of inductance,and the bus voltage correction module is adopted.The vector control simulation model of permanent magnet synchronous motor is built in Matlab/Simulink.Simulations are conducted and has verified the effectiveness of the proposed optimization strategy to improve torque accuracy.Compared with the traditional voltage saturation feedback field weakening control method,the superiority of the proposed strategy in torque output capability in the field weakening region is verified through simulation.In addition,the proposed strategy will be combined with the temperature demagnetization characteristics of permanent magnets,and adopted in the developing the motor high temperature protection strategy in Chapter V.(3)Permanent magnet temperature observer based on thermal network.According to the principle of thermal network method and the characteristics of motor structure,the thermal network model of motor is built and the thermal resistance and heat capacity of motor components in thermal network are calculated.The equivalent circuit of motor thermal network model is constructed by using Simscape module library in Matlab/Simlulink.The speed-torque-loss MAPs of the motor are acquired by electromagnetic finite element software,which are used as the heat source parameter input of thermal network model.Based on the motor thermal network model and the loss MAPs of the motor,a permanent magnet temperature observer is established to estimate the temperature of the permanent magnet.The temperature estimation results will be applied in the Chapter V,the research of the motor high temperature protection strategy.(4)The high temperature protection strategy of motor based on demagnetization characteristics of permanent magnets.The demagnetization performance of permanent magnet material is analyzed.The relationship between the temperature of permanent magnet and demagnetization current is obtained,and the torque limit MAP is obtained by combining the control current map in Chapter III.Combined with the permanent magnet temperature observer and torque limit MAP,the high temperature protection strategy based on the demagnetization characteristics of permanent magnets is formulated.The vector control strategy and high temperature protection strategy proposed in this paper are simulated.Compared with temperature rise results of CFD,the output accuracy of the temperature observer is verified.Compared with the traditional linear power reduction strategy,the proposed high temperature protection strategy can reasonably limit the vector control current,prevent the permanent magnet from demagnetizing failure,and improve the dynamic performance of the motor at high temperature.