Longitudinal Cooperative Adaptive Cruise Control Of Commercial Semi-Trailers' Platoon In Mixed Traffic Conditions

With the development of the highway transportation in China,the number of commercial semi-trailers has gradually increased,and the traffic safety problems are becoming more and more serious.According to researches,forming platoons of commercial semi-trailers on highways by means of cooperative adaptive cruise control(CCAC)system can have a positive effect on traffic safety.In the development of CACC system,mixed traffic flows consisting of CACC vehicles,ACC vehicles and traditional vehicles will exist for a long time in the future.This paper designs a cooperative adaptive cruise control algorithm for commercial semi-trailers platoon based on terminal sliding mode control theory.A vehicle platoon kinematics model and a powertrain model were established to analyze the longitudinal control performance of commercial semi-trailer platoon.Furthermore,taking the failure of vehicle communication in vehicle platoon into consideration,the possible impact of manned-driving and self-driving behaviors on mixed traffic flow is studied with computer simulations using MATLAB/Simulink and TruckSim.In the end,Prescan and Logitech G29 were used to driver-in-loop simulate and verify the control of the controller.In this paper,the hierarchical control system is used to realize the platoon control.The system is divided into the acceleration decision layer and the following vehicle control layer.The acceleration decision layer solves the desired acceleration of the following vehicle according to the real-time spacing,speed,acceleration of the relevant vehicle.The following vehicle control layer uses the desired acceleration,vehicle speed,engine speed,current gear and other information to calculate the throttle opening and the cylinder pressure to achieve following vehicle control.This paper studies the mixed traffic conditions,so the design of the acceleration decision layer is divided into two cases: manned-driving and self-driving.The manned-driving vehicle adopts IDM model.The self-driving vehicle controller is designed based on terminal sliding mode control,so that the tracking error converges to zero in limited time,and the control efficiency is improved.Combined with the constant time headway,by calculating whether the headway error transfer function is greater than 1,it verify whether the speed change will cause the vehicle spacing error of the rear vehicle to expand along the driving direction,and analyses the stability of the vehicle platoon.The following vehicle control layer needs to analyze the moving vehicle force and obtain the influence of the vehicle force on the vehicle state.Then the engine model is established using the map of engine torque characteristics in Trucksim and the normalized fitting is conducted to obtain the normalized function of throttle opening.The braking system model is built by inverting the braking characteristic map and interpolating.Finally,in MATLAB/Simulink environment,the established dynamic model is simulated under two typical working conditions.The results show that the following vehicle control layer has good control effect and can accurately judge the motion state of vehicle accelerating and braking.In order to verify the effectiveness of the designed CACC control system,two forms of simulation are carried out in this paper.Firstly,the co-simulation using MATLAB/simulink and Trucksim is used to analyze the self-driving vehicle platoon and the failure of vehicle communication in vehicle platoon,the latter is mixed traffic conditions of the manned-driving vehicle and self-driving vehicle coexistence.The result shows that the terminal sliding mode control algorithm can achieve tracking of self-driving vehicle and ensure the platoon stability.By adjusting part controller parameters,this algorithm can avoid collision in the mixed traffic conditions to improve vehicle platoon safety.Secondly,driver-in-the-loop simulation is carried out with Prescan and Logitech G29,and analyzes the manned-driving vehicle in the head position and the middle.The results show that the terminal sliding mode control algorithm can achieve the self-driving vehicle platoon tracking and ensure the platoon stability.Combined with the improved control method can avoid collision which platoon suddenly change into a mixed traffic flow and improve the safety of vehicle platoon.