Speed Optimization And Cooperative Control Of Transport Platoon

With the rapid development of China economy,the demand of freight transport has escalated and will continue to grow.The increase in traffic intensity leads to higher fuel use and harmful gas emissions as well as more complex traffic environment.Traffic safety and efficiency has increasingly become a serious issue.Vehicles in cooperative control of platoon can increase traffic capacity and reduce traffic congestion by maintaining small vehicle spacing.In fact,except for the above two functions,the platoon-based driving mode can also reduce the drag coefficient of the following vehicle while decreasing the vehicle spacing,thus by lower fuel consumption and carbon dioxide.However,the potential of the platoon in fuel economy has not received attention.Moreover,subject to the road environment factors such as road gradients and speed limits,it is obviously more reasonable and practical to plan the optimal speed for the platoon control instead of the fixed reference speed.Therefore,in order to ensure the fuel-efficient and stability control of the platoon,this dissertation investigates the fuel consumption optimization,speed planning,string stability conditions,nonlinear dynamics and uncertainty,and platoon coordinated planning in transport platoon system.The main contents are given as follows.(1)The problem of distributed receding horizon optimization control of vehicle platoon is investigated.Considering the fuel consumption optimization and string stability of the platoon,a two-part hierarchical control method is proposed.The first part of the controller is derived in the context of optimal control theory by constructing and solving the optimization problem.The second part of the controller is a complementation of the first part,which is designed based on the platoon string stability analysis.The resulting controller can minimize fuel consumption while maintaining platoon stability.(2)The problem of speed planning and tracking control of a platoon is investigated.The proposed framework is composed of two layers:a speed planning layer responsible for calculating the optimal speed profile and a vehicle control layer for achieving vehicle tracking control.In the first layer,the nonlinear vehicle model is established by considering the road gradient and vehicle nonlinearity.According to the platoon average model and based on a combined optimization cost and dynamic programming method,two speed planning algorithms are designed based on the two sampling mode,time and space respectively.The idea of using an average vehicle instead of the platoon leader for speed planning makes the results more fuel-efficient for heterogeneous platoons.In the second layer,the two controllers are designed and analyzed in a continuous and discrete mode based on the nonlinear vehicle model,and the stability analysis's of the platoon are carried out which corresponding to the time and space-based planning methods in the first layer.In the process of the discrete controller design,a novel platoon string stability criterion is proposed,which makes the designed controller more interesting.Simulation and experimental results have shown that the above two methods can both ensure the fuel economy and stability of platoon.(3)A variable step-size speed planning and model uncertainty of platoon is studied.A two-layered fuel-consumption-optimal solution framework is presented for a platoon of vehicles with unknown nonlinear dynamics.A variable step-size dynamic programming approach is given to solve the optimization problem involved in the speed planning player.The resulted speed profile can achieve a better trade-off between precision and computational cost,and hence,is more fuel-efficient under varying traffic conditions.In the speed tracking control layer,a back-stepping controller based on an adaptive observer is presented,which uses a fuzzy model to approximate the unknown nonlinearity in the system.What makes the control method interesting lies in that it can ensure platoon string stability by controlling the speed tracking errors of the vehicles very small.The effectiveness of the method is demonstrated by numerical simulations and laboratory experiments.(4)The problem of coordinated planning and compound control of platoon is studied.First,the problem is divided into two sub-problems,namely,coordinated planning and platoon control.Correspondingly,a two-layer structure is presented.A cluster-based coordinated planning method is proposed in the upper layer based on vehicle data information and transportation cost savings which fully utilizing the benefits of platoon mode and can further reduce fuel consumption by improving the vehicles formation rate.Considering the influence of the disturbances on the system,the event-triggered model predictive feedforward controller for the large yet low frequency disturbances,and the feedback controller based on the sliding mode control for the low yet high frequency disturbances are designed respectively in the platoon control layer.The resulted feedforward-feedback compound controller can handle disturbance and input saturation constraints on one hand,and ensure platoon stability on the other hand.Finally,the effectiveness of the method is demonstrated by simulations.