Research On Adaptive Coordinated Control Of Vehicle Longitudinal Queue Road Surface

For vehicle platoons,most research scholars focus on the study of control strategies for platoon and simply handle the vehicles in the platoon,which neglecting the nonlinear characteristics of vehicle system dynamics.The intelligent vehicle longitudinal dynamic system is an inherently variable system with complex structure,which is highly susceptible to interference from external factors.In order to reduce the difficulty of the development of control systems,most studies have focused on the hierarchical control structure using upper and lower controllers.However,the vehicle platoon will be affected by changes in the road adhesion coefficient.Therefore,this paper mainly focuses on the problem that when the intelligent vehicle adopts the layered control structure,especially in the road adhesion coefficient,the lower layer controller may not meet the expected requirements issued by the upper controller.Firstly,this paper designs a vehicle adaptive cruise control(ACC)system based on road adhesion coefficient estimation,and discussed and analyzed from the perspective of vehicle safety.Secondly,a coordinated control method is proposed,coordinating the relationship between the safety of the vehicle platoon and the stable slip rate of each vehicle in the platoon,the ability of vehicles to adapt to different road adhesion coefficient under different working conditions is analyzed,which can effectively prevent the vehicle from being locked due to braking on a slippery road surface or slipping due to acceleration.The vehicles in the platoon can finally maintain the same speed and the same safety distance,the stability of the platoon is guaranteed.In order to improve the safety of vehicle adaptive cruise control(ACC)under complicated driving conditions especially under low-adhesion road conditions,and an ACC control scheme based on real-time estimation of road adhesion is proposed.The ACC controller is designed based on the model predictive control(MPC)method where a receding-horizon approach is utilized to compute the desired vehicle acceleration.The real-time estimation of road adhesion coefficient is accomplished by the recursive least square method.A four-degree-of-freedom(4-DOF)longitudinal nonlinear vehicle model is established based on the Lagrangian approach to form the ACC simulation model.The safety of proposed ACC scheme is evaluated by simulations respectively in high and low adhesion conditions.The results reveal that by the proposed adhesion-estimation based ACC system can keep the desired following distance in a wide range of road adhesion conditions.On this basis,this paper further proposes a coordinated control method for vehicle platooning.The traditional hierarchical control structure is replaced by a multi-objective coordinated control structure based on the nonlinear model predictive control(NMPC)method.Firstly,the longitudinal vehicle model is established,then the distance error and the speed difference of the adjacent vehicle,and the difference between the speed of the single vehicle and the wheel speed are established as the control objective of the coordinated control.At the same time,the slip rate of the vehicle wheel is limited to a safe range.The Sequential Quadratic Programming(SQP)method is used to solve the braking or driving torque of the front and rear axles of the vehicle at each sampling moment to control the vehicle.Finally,the proposed vehicle longitudinal coordination control method is evaluated by Matlab/Simulink platform.The results show that the vehicle has good steady-state tracking and adaptability even when driving under low adhesion conditions.