Research On Trajectory Tracking Control Strategy Of Unmanned Vehicle

Nowadays,with the wide application of artificial intelligence,5G and other advanced technologies in the automobile industry,cars are becoming more and more intelligent.The intelligence of cars brings people a lot of convenience,but also improves traffic safety and other issues.Therefore,domestic manufacturers and research institutions have invested a lot of energy in unmanned driving.Unmanned driving technology mainly includes environment perception,trajectory planning and trajectory tracking control.In this thesis,trajectory tracking control technology is studied.Firstly,this thesis introduces the research background and significance of the trajectory tracking control technology of unmanned vehicles,and briefly introduces the development status of the trajectory tracking control method of unmanned vehicles and unmanned vehicles at home and abroad.In view of the research problems of this thesis,the main research content of this thesis is explained and the technical roadmap is made.Horizontal tracking control based on preview LQR and feedforward and longitudinal velocity control based on PID are established respectively for trajectory tracking control.The lateral tracking controller was established based on the two-degree-of-freedom dynamics model and the magic tire model.Because the method could not take into account the dynamics factors of the vehicle and the adhesion of the road surface,it could not guarantee the good stability of the vehicle while tracking the desired trajectory on the low-adhesion road surface and high-speed conditions.To solve this problem,a layered control strategy for trajectory tracking is proposed.The upper controller is the lateral tracking controller based on preview LQR,the middle controller is the direct yaw moment controller based on sliding mode control,and the lower one is the torque distribution and longitudinal velocity controller.The yaw torque controller can make the sidesaw Angle and yaw angular velocity of the vehicle center of mass track their respective ideal values so as to be controlled within the stable range.The torque distribution module distributes the additional yaw control torque generated by the direct yaw torque controller and the driving torque generated by the longitudinal velocity controller based on the proportion of axle load.Due to lateral tracking control in the research,typically longitudinal velocity is treated as a constant,rarely considering the longitudinal velocity influence on lateral tracking control,this thesis is based on three degrees of freedom dynamic model of vertical and horizontal to the coupling through the establishment of horizontal tracking controller model predictive control theory,considering the coupling between the vertical and horizontal to the controller,can be solved in the longitudinal velocity change of operating mode to track the desired trajectory,more in line with the actual driving scenarios.According to the three control strategies established in this thesis,simulation tests were carried out on different roads with different speeds and different adhesion.The results show that the lateral tracking control based on preview LQR and feedforward can stably track the double-shift track at high adhesion and low speed,and the vehicle instability will occur at high speed and low adhesion roads.The trajectory tracking controller based on layered control strategy can improve the instability of vehicles on low adhesion road surface.The model prediction controller based on the 3-DOF dynamics model can stably track the double-shift trajectory under the deceleration condition of low adhesion road surface.