Prescribed Performance Control Of Connected Automated Vehicular Platoons

Connected and automated vehicles(CAVs)platoon control plays a great potential in improving traffic safety,mobility and reducing fuel consumption,and is a key research topic in intelligent transportation systems.Considering the nonlinear characteristics of vehicle dynamics,the performance of vehicular platoon control system is easy to be affected by actuator saturation,disturbances and parameter uncertainties,which can even lead to string instability.Therefore,it is urgent to solve string stability problem of nonlinear vehicular platoon.In addition to steady-state performance of tracking error,transient performance(such as convergence rate and overshoot of tracking errors)is also essential for CAV platoon control systems.However,there are few research results on transient performance.Therefore,this dissertation derives into the issue of prescribed performance control for CAV platooning.The main contents are given as follows:(1)The single prescribed performance adaptive sliding mode vehicular platoon controllers are proposed.For third-order CAV platoon systems with actuator saturation,external disturbances and parameter uncertainties,considering that most traditional platoon control methods only focus on steady-state performances of tracking errors,neglecting the transient performances of tracking errors,with the help of prescribed performance control(PPC)technology,distributed adaptive sliding mode controllers based on single-layer prescribed performance are proposed to achieve different string stability under leader-predecessorfollowing and leader-bidirectional communication topologies.The former can achieve weak string stability by utilizing tracking errors to satisfy prescribed performance constraints,that is,errors are bounded stable.The latter can ensure strong string stability with prescribed performance guaranteed based on coupled sliding mode control(CSMC)method,that is,the tracking errors must not increase along the platoon.By approximating the actuator saturation model with a smooth function,an auxiliary parameter is designed to compensate for input saturation.(2)The dual prescribed performance adaptive sliding mode vehicular platoon controllers and platoon speed optimization are developed.Considering the limitations of platoon controllers based on single prescribed performance which relay on the signs of initial tracking errors and the second-order time derivatives of transformed errors,two performance functions for tracking error variable and coupled sliding mode variable are designed,which are directly related to individual stability and string stability.A low complexity control strategy based on dual prescribed performance is proposed to improve operational efficiency.Considering the influence of non-zero initial tracking error on string stability,a modified spacing strategy based on the relative velocity of the vehicle and the platoon reference velocity is proposed,which converts non-zero initial tracking error situation into zero initial tracking error situation.By introducing an auxiliary system,the effects of input saturation and dual prescribed performance coupling are compensated.Considering road slope and speed limitations,a speed optimization algorithm based on the Pontryagin’s maximum principle(PMP)is proposed to plan reference speed of platoon.(3)The integral sliding mode vehicular platoon controllers based on disturbance observers are proposed.For the vehicular platoon control problems with the constraints of car-following interaction behavior between vehicles and prescribed performance,firstly,considering carfollowing model in traffic flow,an integral sliding mode vehicular platoon controller based on nonlinear disturbance observer is proposed to achieve string stability based on CSMC in frequency domain under constant time headway and bidirectional communication topology.At the same time,the behavior of vehicles in platoon is consistent with traffic flow theory,thereby,avoiding negative spacing errors and so on.Then,in order to improve control performance and achieve traffic flow stability,a prescribed performance vehicular platoon controller based on fixed-time disturbance observer is proposed to achieve string stability in finite time under exponential spacing strategy and leader-bidirectional communication topology.The analysis of string stability can be achieved without the need for Laplace transform.(4)The problem of fixed-time and finite-time prescribed performance vehicular platoon controllers based on backstepping method are proposed.With regard to the convergence speed of nonlinear vehicular platoon systems and the analysis of string stability limitations using frequency domain methods,firstly a new transformed error dynamic system is established by utilizing the convergence relationship between transformed error and tracking error based on PPC and CSMC methods,transforming the problem of string stability into a problem of stabilizing transformed errors,and the chosen performance function relaxes initial tracking error constraints.Then,a distributed fixed-time prescribed performance tracking controller based on sliding mode and backstepping method is proposed under virtual leader-bidirectional communication topology.In order to reduce communication costs,a finite-time tracking controller based on backstepping method is designed under predecessor-following communication topology.These two controllers do not require the second time derivatives of transformed errors,and string stability analysis does not obtain the Laplace transform functions of sliding surfaces,relaxing the restriction on selections of sliding surfaces and applying more advanced and complex sliding surfaces and control methods,which provides new ideas for achieving string stability of nonlinear vehicular platoon.