Traj Ectory Planning And Tracking Control Of Unmanned Vehicle Overtaking

Overtaking has high technical requirements for the driver.When the driver is in the process of overtaking,due to poor mental state or incorrect estimation of the information around the vehicle,the driver will fail to overtake and even cause a traffic accident.In order to improve the driver’s safety during overtaking,this thesis studies the trajectory planning and tracking control methods of driverless cars.Based on the assumption of small angle deflection of front wheel,the linear tire model is introduced to establish the nonlinear vehicle dynamics model,which can accurately express the dynamic characteristics of driverless vehicle when overtaking in lane change,and reduce the computation of trajectory tracking control algorithm.The vehicle driving model is established,and the required throttle opening degree is calculated according to the expected acceleration obtained by the speed tracking controller to realize the vehicle longitudinal speed control.By analyzing the motion relationship between the unmanned vehicle and the vehicle in front when overtaking,the minimum safe distance between the unmanned vehicle and the vehicle in front is calculated based on the acceleration,initial speed,vehicle speed,vehicle distance and vehicle collision time.The overtaking process is divided into three stages:two lane changes and one overtaking.According to the initial speed,speed and distance between the driverless vehicle and the vehicle in front,the target speed,target position and lane change overtaking time of the driverless vehicle are calculated.A three-stage overtaking trajectory is designed for the driverless vehicle by using a quintic polynomial function.Adopt Model Predictive Control(MPC)method to realize unmanned vehicle overtaking trajectory tracking control.According to the three-stage overtaking trajectory planned by the fifth degree polynomial curve,considering the vehicle overtaking condition,the vehicle collision avoidance constraint condition,lateral displacement constraint condition,control quantity constraint condition and other constraint conditions,the reasonable objective function is determined,and the trajectory tracking controller based on model predictive control is designed.According to the actual overtaking experience,the driver will choose to accelerate to overtake the preceding vehicle when overtaking,so the reference speed is introduced when the driverless vehicle overtakes,and a speed tracking controller based on fuzzy PI control is designed.Carsim/Matlab was used to carry out simulation experiments.The simulation results show that the unmanned vehicle can track the target trajectory smoothly and accurately,and the unmanned vehicle can overtake at the reference speed.