Research On Trajectory Tracking Control And Stability Of Unmanned Vehicle

With the rapid development of artificial intelligence and internet technology,as well as the close attention of automobile related manufacturing enterprises and internet technology companies to the field of driverless technology,the research of driverless vehicles has gradually moved towards the development stage of industrialization and practicality.As a high-tech complex integrating environmental perception,decision-making and planning,control and implementation and intelligent network technology,driverless technology can greatly improve road traffic safety and effectively avoid traffic accidents.In different driving scenarios,quickly planning an optimal trajectory through trajectory planning algorithm is the key link to realize unmanned driving technology;In order to realize the stable following of the desired trajectory,the ultimate goal of driverless technology is to design a unified and efficient trajectory tracking control system.Therefore,this thesis studies the trajectory planning algorithm and trajectory tracking control of driverless vehicles in different driving scenarios.The specific research contents are as follows:(1)Trajectory planning algorithm design.In view of the practicability and effectiveness of the trajectory planning algorithm in different driving scenes,this thesis mainly adopts the trajectory planning algorithm combining sampling and polynomial curve interpolation fitting,samples the beginning and end states of vehicle motion in the Frenet coordinate system,solves the quintic polynomial trajectory planning model,obtains the horizontal and vertical trajectory clusters respectively,and synthesizes the trajectory set according to the corresponding sampling time,Finally,using the vehicle kinematics feasibility detection and trajectory collision detection methods,the trajectory set is detected and screened according to the order of trajectory quality evaluation function value from small to large,and a smooth and feasible expected trajectory is obtained.(2)Trajectory tracking controller design.This thesis first establishes the vehicle dynamics model and hub motor model,then designs the speed following controller based on the hierarchical control idea,and uses the hub motor to control the vehicle driving /braking to follow the expected acceleration.Then,based on the model predictive control theory,the vertical and horizontal coupling three degree of freedom dynamic model is used as the prediction model,and the vehicle dynamics constraints are added to optimize the objective function to obtain the front wheel angle control quantity,so as to track the desired path.Finally,combined with the horizontal and vertical control,the desired trajectory is obtained by following the planning.(3)Stability controller design.In view of the instability of driverless vehicles in the process of tracking the desired trajectory under extreme conditions such as variable speed and low adhesion driving,a hierarchical control strategy for trajectory tracking is proposed,which is mainly divided into upper,middle and lower layers.The upper controller mainly tracks and controls the desired trajectory and expected speed,and the middle controller includes vehicle instability judgment module and yaw moment controller,The lower layer mainly distributes the desired longitudinal torque and desired yaw torque to each wheel through the hub motor,so as to ensure the accuracy and stability in the process of vehicle trajectory tracking.(4)Joint simulation analysis.The trajectory planning algorithm is written based on Matlab programming language.The automatic driving toolbox is used to build the surrounding environment of the vehicle,and the visual analysis of different driving scenes is carried out to verify the effectiveness and practicability of the trajectory planning algorithm.The track following controller and stability controller are built through Carsim /Simulink and other joint simulation platforms to analyze the track following ability of the vehicle in relevant driving scenes,as well as the track following accuracy and driving stability of the vehicle under variable speed and different attached road driving conditions,and compare and analyze the effectiveness and safety of the track tracking stability control strategy.