Research On Stability And Energy Efficiency Optimization Control For Distributed Drive Electric Vehicle

With the progress of science and technology and the continuous improvement of people’s requirements for automobile performance,the research and development of new energy vehicles is gradually becoming the focus of the global automotive industry.Electric vehicles not only represent the development trend of automobile technology in the future,but also the key technical way to deal with many challenges faced by the development of automobile industry,such as energy conservation and environmental protection.Distributed electric drive vehicle has become a research hotspot because of its short transmission chain,strong controllability,fast response and green environmental protection.However,how to accurately control the highly redundant control system of distributed electric vehicle,prevent the mutual interference of different control systems,realize the coordinated control between multiple actuator systems and multiple control objectives,and reasonably distribute the torque of four hub motors and the output of each subsystem is a research direction and hotspot of distributed electric vehicle chassis control.At the same time,how to maintain the stability and handling performance of the vehicle with minimum energy consumption under various driving conditions puts forward higher requirements for the integrated control of handling stability control and energy efficiency optimization of distributed electric vehicles.Taking distributed electric vehicles as the research object and based on vehicle dynamics theory,aiming at the characteristics of high controllable degrees of freedom of distributed electric vehicles,this paper carries out theoretical and application research on multiple levels of vehicles,such as state and parameter estimation,stability judgment,integrated control of handling stability and energy efficiency optimization,multi subsystem and multi-objective collaborative control.The main research contents and conclusions are shown as follows:(1)An observer is designed based on extended Kalman theory(EKF).The observer can observe the vehicle longitudinal speed,sideslip angle of mass center,tire lateral force and other state parameters in real time.To obtain the accurate rollover index of the vehicle,it is very important for the accurate control of roll stability.Considering the uncertainty of vehicle sprung mass,the observer can provide real-time estimation of vehicle rollover angle,rollover angle speed and vehicle mass for the control system,so as to calculate the accurate rollover index.(2)A hierarchical control strategy of handling and stability based on variable wheelbase reference modes is designed.The control strategy includes three layers.The upper controller includes variable wheelbase judgment module,reference modes module,vehicle stability judgment controller,speed tracking controller and fuzzy logic controller.The middle-level controller includes four-wheel independent steering system(4WIS)sliding modes controller and adaptive LQR controller.The bottom controller adopts the optimal torque distribution strategy to distribute the driving /braking torque to four wheels.The hierarchical controller simulates and analyzes the coordinated control strategy of 4WIS system integrated control and LQR system on Simulink / Car Sim platform.The simulation results show that the proposed control strategy can improve the flexibility of electric vehicle under small turning radius,improve the lateral stability and handling performance of electric vehicle under high-speed condition,and make full use of four-wheel independent steering system.(3)An integrated control strategy based on modes predictive control and active steering system is designed.The integrated control system can realize the coordinated control between energy efficiency optimization control and lateral stability control under various working conditions.The integrated control system includes a global search module for motor instantaneous efficiency optimization,which can obtain the optimal torque distribution of the front and rear axles of the vehicle.At the same time,a terminal sliding modes controller is designed to maintain the lateral stability of the vehicle under general working conditions.The modes predictive controller realizes the coordinated control between the active steering system and the direct yaw moment control system(DYC),which can reduce the large additional yaw moment demand of the vehicle under the condition of high-speed turning,and the energy-saving optimal torque distribution algorithm is adopted in the bottom controller to reduce energy consumption.Finally,the effectiveness of the integrated control system based on modes predictive control and active steering system is verified on Simulink / Car Sim platform.Through the verification of various test conditions,the energy-saving integrated control strategy can not only improve the lateral stability of the vehicle under various conditions,but also optimize the energy consumption of the vehicle.In constant speed sinusoidal steering maneuvering condition,the energy consumption of the energy-saving integrated control strategy can be reduced by 21.66%.(4)A multi-objective control strategy based on multi execution system integration is designed.The integrated control system can realize the coordinated control of multiple actuators of the vehicle,and improve the control performance of multiple control targets such as lateral stability,handling performance,rollover stability and trajectory tracking of the vehicle.The control strategy can prevent the interaction between different execution systems and the conflict between different control objectives.Secondly,the integrated control strategy considers the uncertainty of vehicle sprung mass in the calculation of roll index,analyzes the influence of vehicle mass change on multi-objective integrated control system,and uses variable wheelbase reference modes technology to reduce the rollover index of vehicle under extreme working conditions.Finally,the effectiveness of multi-objective control strategy based on multi execution system integration is verified on Simulink / Car Sim platform.