Research On The Overtaking Control Method For Autonomous Vehicle On Highway

With people’s continuous pursuit of safe and comfortable driving experience,and the great potential of autonomous vehicle technology in alleviating traffic congestion,reducing traffic accidents and improving road utilization rate,autonomous vehicle technology has become an important research direction of today’s automobile industry.Based on the development status of autonomous vehicle technology,this thesis deeply studied the autonomous vehicle overtaking control method in expressway environment.Aiming at the behavior decision-making,trajectory planning,trajectory tracking and other problems in the process of overtaking,this thesis puts forward some autonomous vehicle overtaking control method,and constructs the overtaking behavior model of autonomous vehicle,which enabled the vehicle to overtake autonomously according to the surrounding traffic environment.In terms of the overtaking behavior decision-making of autonomous vehicle,by analyzing the overtaking process of human drivers,the overtaking behavior was discretized into four sub-behaviors,namely lane change preparation,lane change,overtaking and merging,so as to transform modeling complex decision-making problem into the state transition relationship between sub-behaviors.According to the finite-state mechanism,a model of overtaking behavior was built to make the modeling more logical,which reduced the complexity of overtaking behavior decision-making.In terms of safe driving distance,the minimum safe distance was calculated based on the condition of anti-collision during the process of lane changing,and the final safe driving distance is determined according to the actual situation,which ensure the safety of lane changing behavior.The safe driving distance also assisted the decision-making of overtaking.In the aspect of trajectory planning,considering the constrains of vehicle during the process of lane changing,this thesis compared the advantages and disadvantages of the lane changing trajectory used by the existing lane changing model,and finally selected the fifth degree polynomial to fit the vehicle lane changing trajectory,finally fitted the corresponding driving trajectory for each sub-behavior of overtaking.In the aspect of trajectory tracking,firstly built the 3-dof nonlinear dynamic model of vehicle and discretized the dynamic model to serve as the model prediction controller prediction model.Secondly,analyzed the constraints existing in the process of vehicle driving,including the constraints of the vehicle itself and the driving environment.Then construct the objective function,for sometimes the optimal solution cannot be obtained,the relaxation factor was added into the objective function.The trajectory tracking controller was designed according to the dynamic model,constraint conditions and objective function.Jointing simulation model and design different working condition,including different speed and road adhesion coefficients,to verify the effect of the trajectory tracking controller.Finally,by combining the overtaking behavior decision model,safety distance model,overtaking trajectory planning model and trajectory tracking controller,the simulation model of autonomous vehicle overtaking behavior was built based on CarSim and Matlab/Simulink.Then designed four different working conditions to verify the effectiveness and reliability of the autonomous overtaking control method studied in this thesis.The simulation results show that the proposed control method could guide the autonomous vehicle to overtake autonomously.