Research On Distributed Electric Vehicle Torque Coordination Control Based On Improving Vehicle Stability

The invention of automobile has greatly promoted the development of human society,but in recent years,the rapid growth of the number of automobiles has also brought serious energy and environmental problems.Electric vehicles have attracted more and more attention because of their use of renewable energy as a power source and characteristics of non-emission pollution.Distributed electric vehicles can drive wheels directly by hub motors without chassis transmission system,and each wheel torque can be controlled independently.The structural advantages of distributed electric vehicle make its related control technology become the focus of many scholars.Aiming at the control problem of distributed electric vehicle,this paper studies yaw moment control and torque optimization based on model predictive control method of distributed electric vehicle.Specific research contents are as follows.(1)To study the stability of electric vehicles,the dynamic characteristics of distributed electric vehicles are analyzed.According to the vehicle's characteristics,the vehicle's motion freedom is simplified,and the lateral and longitudinal and the wheel's rotation dynamics characteristics are analyzed based on the Seven degree of freedom model.Magic tire model,motor model and driver model are built in Simulink.Carsim is used to build the body model of electric vehicle,Carsim-Simulink simulation platform is established by combining the motor model established in Simulink.Verification under typical working conditions,and provides a basis for the research of vehicle stability control system.(2)Vehicle stability analysis.The yaw rate and sideslip angle are determined as the evaluation index of vehicle stability.A two degree of freedom reference model is established to provide reference for stability evaluation parameters.The influence of wheel torque distribution on vehicle stability is analyzed.(3)Considering the problem of wheel sliding,a hierarchical control strategy for the stability of distributed electric vehicle is designed.The upper layer uses the fuzzy control method design the fuzzy yaw moment controller.Takes the errors of ideal yaw rate and actual yaw rate,ideal sideslip angle and actual sideslip angle as the input of the fuzzy controller.The required yaw moment as the output.In the middle layer,the model predictive control method based on state space is used to optimize the wheel torque correction.The whole vehicle model is analyzed,the state and control variables are selected,the state space predictive model is established,and the optimal controller based on the predictive model is designed.The reference input of the controller is the required yaw moment obtained by the upper controller,and the output is the variation of the motor torque.Considering the constraints of vehicle lateral stability and tire sliding,the quadratic objective function is solved on-line.The lower layer is the executive layer of the hub motor's torque control,including the motor and its controller.The middle layer's torque input is coordinated with the driver model requirement Torque input to achieve real-time vehicle stability control.(4)The simulation platform based on Carsim/Simulink is used to simulate and analyze the vehicle stability of distributed electric vehicles under unstable control,PID control and hierarchical control.The analysis results show that the designed control strategy is superior to the uncontrolled and PID control in stability control.