Formation Control And Stability Analysis Of Connected And Automated Vehicle Platoon

Intelligent and Connected Vehicles(ICVs)that contain the technologies of autonomous vehicles and wireless communication is one of the main methods to approach Intelligent Trans-portation(IT),which has important research value in solving the problems of road congestion,vehicle accidents,and so on.As an important application of ICVs,the vehicle platoon system can realize the cooperation of multi-vehicles in perception,decision-making,and control,which has a great role in promoting the safety,energy conservation,comfort of vehicles,as well as in improving road traffic efficiency.According to control consequences,vehicle platoon control can be divided into platoon forming control(PFC)and platoon stability control(PSC).Among them,PFC focuses on how to make vehicles in different states to form a platoon safely and smoothly,which is the premise to achieve PSC.PSC is centered on maintaining vehicles to run steadily with the desired speed and geometry,which is a necessary condition to ensure vehicle safety and improve traffic efficiency.In the past decade,many works have been done about PFC and PSC.However,because of the complexity of the traffic environment and the non-linear coupling relationship between vehicles,there are still some unresolved problems in vehicle platoon control.Firstly,when vehicles run on a different lane with arbitrary speed,the current PFC is difficult to control vehicles to form a platoon safely and efficiently.Secondly,when there are multi-interferences and communication delays,the stability of the longitudinal platoon system is hard to be maintained by the traditional PSC.Thirdly,the existing modeling and control method in PSC can not solve the coupling problem of longitudinal and lateral vehicle dynamics when the vehicle platoon runs along a curved road.At last,the objectives of vehicles' energy-saving and platoon stability can not be realized simultaneously in the current PSC.To resolve these problems and provide the theoretical and methodological supports for distributed control of vehicle platoon system,in this paper,the formation control and system sta-bility analysis under multiple factors are studied respectively,from maintaining vehicle stability in vehicle platoon formation,guaranteeing the longitudinal stability of vehicle platoon under multiple disturbances and delays,realizing the longitudinal and lateral decoupling control of the curved heterogeneous platoon,and achieving energy saving and stability of platoon at the same time.The design of a distributed motion controller and performance analysis of the closed-loop system for the vehicle platoon system are also done.The research work and contributions of this paper can be divided into fourfold.(1)For the formation control of the vehicle platoon system with different vehicle states,according to the mechanism of multi-agent formation control,the relationship between vehicle dynamics system stability and multi-agent formation control is explored.A multi-vehicle formation control system is constructed based on the distributed hierarchical control method to realize the stability and high-efficiency of vehicle platoon formation.To address the problems of lateral instability and actuator saturation of the vehicle,a stable and efficient distributed platoon control system,which includes distributed tracking controllers to realize the stable planning and tracking of vehicles' states,is designed based on vehicle stability boundary and multi-agent formation control algorithm.(2)To ensure the longitudinal stability of a vehicle platoon system under multiple distur-bances and delays,a new heterogeneous platoon model that contains disturbances,communica-tion delays,and parameter uncertainties is established first.By using the method of equivalent delay,network-induced delay and structural uncertainties,the factors that have a great impact on the platoon stability,such as road gradient,air resistance,communication delay,and data packet loss,data discretization characteristics of vehicle sensors,and so on,are integrated into the heterogeneous platoon model.Then,based on Lyapunov-Krasovskii stability theory and H? robust control,an inner-vehicle stability controller with weak conservativeness is proposed to reduce the effect of external interference and communication delay.The sufficient condition of maintaining inner-vehicle stability of a heterogeneous platoon system under multiple distur-bances and communication delays is also given.To ensure the string stability of the platoon system under the disturbances and communication delays,a concept of L2 string stability of the platoon system is proposed,and the string stability criterion of heterogeneous platoon model under disturbance and time delay are presented.(3)Given the lack of research on the stability of the curved platoon system,the longitudinal-lateral decoupling control and stability analysis of the curved platoon are studied.First,based on the feedback theory of the non-linear system and the geometric relationship of the curve platoon,the platoon following model and platoon lateral road tracking model are constructed,which include road information.The effects of communication delay and packet loss,road gradient,and external wind to the curved platoon system are considered in the process of system modeling.To achieve stable platoon control on a curved road,the platoon uses the state-feedback control method in the longitudinal direction while each vehicle tracks the centerline of the curved road to realize lateral control.Longitudinally,an H? platoon controller is designed based on the Lyapunov-Krasovskii functional to ensure the inner-vehicle and string stability of the platoon,which suffers from parameter uncertainty,and external disturbances.Additionally,the L2 string stability is defined to guarantee that the perturbations do not grow unbounded as they propagate through the platoon.(4)To minimize the energy consumption of each vehicle while ensuring the platoon string stability under external interference and communication delay,a discrete control framework for a homogeneous vehicle platoon is presented.First,a novel variable spacing strategy named the energy-oriented spacing policy is proposed by comparing the geometry relationship of each vehicle which drives at energy-optimal speed and the ideal speed under the constant spacing policy.Then,based on the energy-oriented spacing policy,the dynamics of a homogeneous discrete vehicle platoon composed of several pure electric vehicles are built,including the communication delay and external disturbance.Second,a discrete robust platoon controller that can reduce the conservatism of the control system is designed based on the Lyapunov-Krasovskii theorem and H? method,which drives each vehicle at their energy-optimal speed while ensuring the string stability of platoon under communication delays and interferences.Third,the L2-based string stability of the discrete platoon is defined,and its string-stable criterion is given under communication delays and external disturbances.(5)A miniaturization platform of vehicle platoon system is built,and tests are carried out for longitudinal stability,and longitudinal-lateral coupling control of the vehicle platoon system is proposed in this paper.The results show that the proposed methods can guarantee the stability of the vehicle platoon system on straight and curved roads respectively.