Research On Obstacle Avoidance Trajectory Planning And Motion Control Algorithm Of Autonomous Vehicle

Automobile automation has become an important development direction in the field of automobile and transportation.Improving vehicle driving safety has always been one of the main purposes of the development of autonomous driving technology.Autonomous vehicles can effectively improve vehicle driving safety and reduce the incidence of traffic accidents through active obstacle avoidance,and trajectory planning and motion control are the two core technologies of autonomous vehicles to achieve this function.Structured roads are generally considered to be the best scenario for commercial adoption of autonomous vehicles.Therefore,this paper focuses on trajectory planning and tracking control of autonomous vehicles in structured road scenarios.The main research contents are as follows:In the trajectory planning part,this paper uses the path-velocity decomposition method to transform the three-dimensional space-time trajectory planning problem into two twodimensional problems.For the path planning problem,this paper adopts the solution strategy of decision first and planning later.Firstly,a smooth and evenly spaced reference line is extracted from the global path using the reference line generation algorithm.Frenet coordinate system is constructed based on the reference line,and then the SL graph is further constructed.In this way,the planning problem is transformed into the problem of finding the optimal path in the SL graph.In the decision-making part,the improved Weighed A* algorithm is used to search the initial path in the rasterized SL graph,and according to the initial path,the decisionmaking mode of the car when facing obstacles can be determined.In the planning part,the solution space of the numerical optimization problem is developed based on the initial path and combined with the road boundary.The objective function is designed according to the trajectory optimality index,and the constraint function is designed according to the curvature continuity,safety and other constraints.The optimization problem is constructed into a quadratic programming problem for solving,and the optimal path satisfying various constraints is obtained.For the speed planning problem,the strategy of decision first and planning later is also adopted.Firstly,the ST diagram is constructed based on the result of path planning,and the problem of planning is transformed into the problem of finding the optimal path in the ST diagram.In the decision-making part,the dynamic programming algorithm is used to search for an initial speed curve in the ST graph discretized by the segmented sampling strategy,and then the decision of racing or giving way when facing dynamic obstacles is determined.In the planning part,the convex space of the numerical optimization problem is developed on the basis of the initial velocity curve.The objective function is designed according to the trajectory optimality index,and the constraint function is designed according to the constraints such as the continuity of the velocity curve,disallowed reversing and vehicle dynamics.The optimization problem is constructed into a quadratic programming problem for solving,and the optimal velocity curve satisfying various constraints is obtained.In the motion control part,in order to reduce the complexity of the controller,the control strategy of horizontal and longitudinal control decoupling is adopted.In order to improve the control accuracy and robustness,MPC algorithm is adopted in both vertical and horizontal controllers.The vertical controller adopts a layered design strategy.The upper controller is designed based on the MPC algorithm,and the lower controller is designed based on the vehicle longitudinal dynamics model.The upper and lower controllers cooperate to realize the longitudinal speed control.In the algorithm verification part,Carsim,Matlab and Prescan are used for co-simulation.Simulation verifies the safety,comfort and feasibility of the trajectory planned by the obstacle avoidance trajectory planning algorithm described in this paper and the control accuracy,comfort and stability of the motion control algorithm in the process of vehicle driving.