Research On Cooperative Adaptive Cruise Control With Communication Delay

Cooperative adaptive cruise control is an expansion technology of traditional adaptive cruise control with the application of the Internet of Vehicles.Through data interaction and coordinated control between neighboring vehicles,CACC system controls vehicle to drive in the form of vehicular platoon with small following headway,which has significant advantages in improving traffic efficiency,reducing energy consumption,ensuring travel safety,and optimizing riding experience.In the research of cooperative adaptive cruise control,the communication performance has a significant impact on the following accuracy and stability of the vehicular platoon.And the coupling relationship between the communication delay,the following time distance,and the string stability makes the communication delay have a great influence on the string stability margin,and also leads to a stringent limit on the minimum allowable following headway.Consequently,it is difficult for the CACC control strategy to ensure the string stability under the small following headway,which obviously weakens its advantages in reducing the following distance and improving the traffic efficiency.In addition,the traditional time-triggered CACC control strategy has the problem of ineffective and excessive consumption of limited communication resources,which may easily lead to communication channel congestion and aggravate communication delay.Furthermore,how to design the robustness of the controller for the perturbation of vehicle dynamics parameters and the differentiated following headway in the human-vehicle system is also a key problem to be solved in the design process of cooperative adaptive cruise control.Based on the in-depth analysis of the requirements and implementation difficulties involved in the following strategy of vehicular platoon,a robust control strategy for cooperative adaptive cruise is firstly designed by adopting the parameter space approach,which solves the robustness design problem of the controller under the requirements of multiple performance indicators and the uncertainty of multiple parameters;On this basis,an optimization strategy based on time delay predictive compensation is designed to improve the string stability margin and reduce the minimum allowable following headway.In addition,an event trigger mechanism is further designed to reduce the occupancy rate of communication resources to avoid channel congestion and reduce communication delay.The specific research contents are as follows:Firstly,the four-element architecture is applied to model the complex configuration the vehicular platoon,and the robust CACC controller design method based on the parameter space method is proposed.Based on the four-element architecture,the vehicular platoon is modelled from four parts: node dynamics,queue geometry topology,communication topology,and CACC controller;Through the analysis and comparison of the strategies for each part,hierarchical vehicle node dynamics control method,fixed following headway strategy,PF communication topology and feedforward-feedback CACC controller are adopted;A robust design method is proposed,which can consider the performance requirements(internal stability,chord stability and following accuracy)in both the time and frequency domains of the system,and the parameter space method is adopted to derive the feasible region of the controller gain in the presence of parameter uncertainties.Secondly,a robust cooperative adaptive cruise control strategy based on parameter space approach is designed to ensure the stable following effect of vehicular platoon under the influence of communication delay,dynamic parameter perturbation and differentiated following headway.The communication delay is equivalent to the external disturbance of the system,and the maximum disturbance to the system is represented by the maximum communication delay,and then the influence of the communication delay on the internal stability,following accuracy and string stability of the CACC control strategy is analyzed;To deal with the influence of communication delay,dynamic parameter perturbation and differentiated following headway,-stability,(?)-stability and (?)-string-stability are defined and the feasible region of CACC controller gains that meet the design requirements under the joint influence is derived by parameter space approach;According to the change rule of the feasible region of the controller gains under different following headway,a gain scheduling strategy is designed to meet the requirementss of differentiated following headway and effectively reduce the conservatism of the system.Thirdly,a cooperative adaptive cruise control strategy based on time delay predictive compensation is designed to realize the decoupling between communication delay,following distance and string stability considering the dynamic parameter perturbation,which improves string stability margin and lowers the minimum allowable following time limit.A time delay predictive compensation control strategy combining the "Master-Slaver" architecture and the Smith predictor is proposed to compensate the communication delay after transferring it to the system feedback section,which effectively realizes the stable following effect with the zero following headway and any communication delay under the premise of accurate estimation.The sensitivity of the time delay predictive compensation control strategy to estimation deviation of communication delay and dynamic parameters is analyzed,adopting the minimum allowable following time as the evaluation index;The disturbance observer is designed to compensate the interference caused by the perturbation of vehicle dynamics parameter and to reduce the prediction deviation,thereby improving the following performance with small following headway when dynamic parameter perturbation exists.Fourthly,a cooperative adaptive cruise control strategy based on event trigger mechanism and an adaptive control strategy for communication packet loss are designed to achieve the balanced coordination of communication resource utilization and control performance.An event triggere strategy based on the degree of acceleration change is constructed,and the CACC model triggered by the event is established by disturbance modeling method;The disturbance boundary caused by the event trigger mechanism is determined,and the method to solve the feasible region of the CACC controller gains that meets the requirements of following accuracy and string stability under the event trigger mechanism is proposed;Considering the high sensitivity of the event-triggered scheme to communication packet loss,a random packet loss model under the event-triggered scheme is established,and the change trend of the disturbance boundary and its influence on the feasible region of the controller gains are analyzed;An adaptive following headway strategy and an adaptive event triggered threshold strategy under non-ideal communication environments are proposed to realize the coordination of communication resource utilization,traffic efficiency,with following performance and safety in the case of communication packet loss.Finally,the verification framework of cooperative adaptive cruise control strategy including co-simulation,herdware-in-loop tests and vehicle experiments was established.Car Sim/Simulink co-simulation and d SPACE-based hardware-in-the-loop testing are carried out,and an intelligent vehicle equipped with LTE-V is developed for real vehicle testing.The test results of UDDS,EUDC simulation conditions and real vehicle variable speed driving conditions fully verify that the CACC control strategy proposed in this research can effectively deal with the influence of communication delay,dynamic parameter perturbation and differentiated vehicle following time distance,and ensure vehicle formation following accuracy,driving smoothness and communication resource utilization.