Research On Nonlinear Modeling Of Vehicle Permanent Magnet Synchronous Motor Based On Magneto-Thermal Coupling

As the key part of electric vehicle,motor controller determines the operation efficiency and safety of motor,as well as the performance of speed regulation system.In the early stage of motor controller development,it is essential to test the characteristics of the controller,but the existing test system has many shortcomings,such as complex structure,high hardware cost,long cycle and so on.In order to cope with the these questions,there is a motor simulator system that uses power electronic technology to simulate the motor and its mechanical load.One of the keys to whether the motor simulator can simulate the real characteristics of the motor is to establish an accurate and efficient motor model.At present,the vehicle permanent magnet synchronous motor model mostly adopts linear model,which does not take into account the changes of motor electromagnetic parameters in magnetic thermal coupling and the influence of parameter changes on control,and can not effectively reflect the real running state of the motor.Therefore,it is particularly important to establish an accurate and efficient nonlinear model of motor.Firstly,the structure of permanent magnet synchronous motor is analyzed,and based on the linear model,the nonlinear model of motor under magnetothermal coupling is deduced,including voltage equation,flux linkage equation and torque equation.Based on the finite element calculation,the influence of nonlinear factors on the electromagnetic parameters of the motor is studied,the relationships between resistance and temperature,inductance and current temperature,permanent magnet flux and temperature and current are obtained,which provides a theoretical basis for the nonlinear modeling of motor.Secondly,using the principle of motor heat transfer,the dynamic thermal network model of the motor is built,and the thermal resistance and heat capacity in the thermal network model are calculated according to the actual structure and material characteristics of the motor.Simultaneously,the simulation is carried out on the MATLAB/Simulink platform to analyze the temperature rise of the motor under no-load and loading conditions.It can be seen that the motor winding temperature is the highest,the rotor is the second,and the shell is the lowest.In addition,the accuracy of the thermal network model is proved by the motor temperature rise test.Then,through the finite element calculation results,the relationships between resistance and temperature,inductance and current temperature,permanent magnet flux and current temperature are established.According to the built thermal network model,the input of temperature parameters is obtained,and the relationship between electromagnetic parameters and temperature and current is established by look-up table method.Meanwhile,the nonlinear model is discretized by backward Euler method,and the model interface is encapsulated,so the nonlinear ontology model of permanent magnet synchronous motor is obtained.Finally,the control strategy of maximum torque current ratio is analyzed.Based on the nonlinear ontology model of permanent magnet synchronous motor,the control model is established.In the meantime,the whole nonlinear system is simulated based on the control algorithm of maximum torque current ratio,and the performance of the motor at different temperatures is obtained.The influence of nonlinear electromagnetic parameters of the motor on the system output is analyzed,and the relationship between stator current and output torque is obtained.Finally,through the experimental platform,the effective values of current,torque and speed waveforms under steady-state and dynamic conditions of the motor are compared with the simulation results.Compared to the linear model,the nonlinear model is closer to the actual experimental value and can better reflect the actual operation condition of the motor.