Research And Implementation Of Key Technologies For Coordinated Control Of Longitudinal And Lateral Motion Of Distributed Drive Electric Vehicle

With the strict requirements of environment and energy,electric vehicles have become the trend of automobile industry development in a long period of time.The research direction is accelerating to the development of electric,intelligent and lightweight.Compared with the electric vehicle driven by centralized motor,the distributed drive electric vehicle has the characteristics of high transmission efficiency,compact structure,independent and controllable driving and braking torque of each wheel,and more stable and efficient power output.It is considered to be one of the main means of transportation for low-carbon society and smart city in the future.The distributed drive electric vehicle cancels the mechanical connection of the transmission system and are directly driven by four independent in-wheel motors,which plays an important role in improving the controllable range of vehicle stability and is of great significance in improving the driving stability and handling performance.In the aspect of handling and stability control of distributed drive electric vehicle,the coupling among steering,driving and braking and the fault of in-wheel motor must be considered.In order to improve the handling performance and driving stability of distributed drive electric vehicle,this dissertation studies the coordinated control of distributed drive system,braking system and active front wheel steering system.Based on the analysis of the current situation of vehicle handling stability control,this dissertation summarizes the shortcomings of the current research and completes the following related work:(1)The dynamic modeling and verification of the distributed drive electric vehicle are completed,and the"vehicle-tire"seven degree of freedom model which can reflect the vehicle handling stability is established by using the model-based method,the neural network driver model is used to simulate the driver in the loop under normal and extreme conditions on the standard double lane changing road,and the rationality and availability of the distributed drive electric vehicle dynamics model are verified.(2)The coordinated control strategy based on the phase plane stability discrimination method is designed to improve the handling stability of distributed drive electric vehicle under complex driving conditions.The mathematical expression of dynamic stable boundary are established by orthogonal simulation,which solves the problem of poor robustness of static boundary.According to the divided dynamic stability boundary,a coordinated control strategy based on the active front wheel steering and the direct yaw moment is designed,which coordinates the control weights among classical stability domian,extended domain and non domain.Aiming at the strong coupling phenomenon between the execution systems in the non domain,an inverse system decoupling controller is designed to eliminate the strong coupling effect of the two execution modes.In addition,in order to improve the accuracy of in-wheel motor control,the motor torque active disturbance rejection controller is designed to improve the robustness of torque control and solve the problem of poor torque execution accuracy caused by external disturbance and motor steady-state error.(3)The coordinated control strategy of torque vector control and electronic stability control is designed to improve the handling stability of distributed drive electric vehicle under complex conditions and reduce the longitudinal speed loss.The dynamic envelope boundaries are designed according to the critical point of the phase plane and the constraint of the tire side slip angle,and the mathematical expression is carried out,and the distance from the coordinate of the vehicle state to the envelope boundary are quantified.The execution error of four in-wheel motors are considered as external disturbance,and a robust_?dynamic output feedback controller is used to design the torque vector control system of in-wheel motor,which enhances the execution accuracy and robustness of the torque control.The control method of self-tuning PID parameters by improved ant colony algorithm is adopted to design the electronic stability controller,which takes into account the global search speed and local search accuracy.A state observer based on the unscented Kalman Filter algorithm is designed to overcome the difficulty of solving Jacobian matrix in the linearization process of traditional extended Kalman Filter algorithm.(4)Based on the functional safety technology,a handling stability control strategy is designed which considers the fault behavior of in-wheel motor.By establishing the vehicle dynamics model including the motor failure,it is found that the corner mutation and the additional yaw moment caused by the gain fault of the front axle single motor will cause the vehicle stability to be poor and serious deviation,and the simple driving torque truncation control can not make it return to the ideal state quickly.Based on the dynamic analysis,the steering by wire control system is designed.The angle tracking performance of the steering by wire system is improved by the variable intercept sliding mode control algorithm,and the chattering phenomenon of the system are reduced.The adaptive fault diagnosis observer is designed to diagnose the in-wheel motor fault of the driving system in real time,and then the model predictive control algorithm is used to redistribute the driving torque to achieve the longitudinal and lateral state tracking.(5)The in-wheel motor hardware in the loop platform is built based on the NI-PXI real time system,and the distributed drive electric vehicle platform is built based on the NI Compact RIO virtual control prototype.The coordinated controller of the active front wheel steering and the direct yaw moment,the coordinated controller of the torque vector and the electronic stability and the coordinated controller considering in-wheel motor gain fault are tested respectively.The test results show that the coordinated control of the active front wheel steering and the direct yaw moment can improve the vehicle handling performance and stability at the same time under different driving conditions.The coordinated control of the torque vector and the electronic stability can reduce the loss of longitudinal speed while controlling the stability.The coordinated controller considering the in-wheel motor gain fault ensures the stability of the vehicle after the motor failure,and can restore the steering performance to track the desired route.