Research On Torque Allocation Strategy Based On Dynamic Loss Model Of Electric Drive System

At present,the steady-state numerical model of pure electric vehicle based on the motor bench experiment,which only considers the loss of motor and inverter,is defective in the research of torque allocation strategy,which cannot minimize the loss of electric drive system.At the same time,the influence of battery dynamic characteristics and motor temperature changes on the loss of the electric drive system is not considered,which leads to the failure of torque allocation strategy to guarantee the real-time economic optimization of the vehicle under any working condition.Therefore,this paper will analyze the loss mechanism of inverter,motor and transmission system,and comprehensively consider the influence of dynamic characteristics of battery and motor temperature to establish the dynamic loss model of "three-in-one" electric drive system.Based on the dynamic loss model of electric drive system,the real-time optimal torque allocation strategy of pure electric vehicle will be studied.Firstly,the structure and control structure of the electric drive system are analyzed.Based on the loss mechanism of inverter,motor and transmission system,the loss model of electric drive system was established by combining Motor＿CAD and Matlab/Simulink software.A battery equivalent circuit model considering the open circuit voltage characteristics and internal resistance characteristics was established to describe the dynamic characteristics of the battery.Combined with the driver and the vehicle dynamics model,the forward simulation model of the vehicle is established,which lays the foundation for the research of torque distribution strategy.Then,based on the loss model of the electric drive system,the particle swarm optimization algorithm(PSO)was used to optimize the motor torque distribution coefficient under each driving/braking condition,aiming at minimizing the loss of the electric drive system,and the off-line torque distribution strategy with the minimum loss of the electric drive system was obtained.At the same time,based on the steady state efficiency numerical model of the motor and the inverter,aiming at the optimization of the motor and the inverter efficiency,the method of traversal optimization was adopted to obtain the off-line torque allocation strategy for the optimal motor system efficiency.The advantages of the off-line torque allocation strategy based on the minimum loss of the electric drive system are verified by comparing and analyzing the two off-line optimal torque allocation strategies.Then,based on the battery equivalent circuit model and motor vector control theory,the influence of different terminal voltages on the motor current control strategy is analyzed.The influence of temperature on motor loss and torque performance was analyzed by finite element model of motor.According to the heat generation and heat transfer mechanism of the motor,the equivalent thermal network model of the motor is established to estimate the winding temperature and the temperature of the permanent magnet.The dynamic loss model of the electric drive system was established by comprehensively considering the effects of battery terminal voltage,internal resistance characteristics,motor winding and permanent magnet temperature changes on the loss of the electric drive system.Finally,based on the dynamic loss model of the electric drive system,an online torque allocation strategy with the minimum loss of the real-time electric drive system was proposed,and the effects of battery voltage and motor temperature on the torque distribution coefficient were analyzed.The economy of online torque distribution strategy and two offline torque distribution strategies were compared and analyzed.Based on the collected test road data,typical road driving conditions were constructed to verify the adaptability of online torque distribution strategy in driving conditions.