| Adaptive cruise control(ACC)system,developed by cruise control system,is an active safety technology which can effectively reduce driver fatigue and improve vehicle safety.As a new generation of auxiliary driving system,adaptive cruise control system can not only reduce driving burden,reduce traffic accidents caused by wrong driving and fatigue driving,improve riding comfort,but also increase road traffic capacity on existing infrastructure,reduce fuel consumption and exhaust emissions.Therefore,the research and optimization of adaptive cruise control system is of great value and significance,whether from the perspective of human,traffic or environment.The initial adaptive cruise control system,considering only the safety and the performance of following vehicle,mainly uses the radar and other sensor systems to obtain the speed of host car,the speed difference and the vehicle distance between head car and host car,then control the longitudinal speed of the host car,and most applying in the vehicle can be opened at a certain speed or above,and are only suitable for simple working conditions.However,from the driver’s point of view,the vehicle performances of ride comfort and fuel economy are also very important evaluation indicators.Therefore,in order to adapt to the complex and changeable scenarios of urban working conditions,based on the existing PID control algorithm,this paper explores an adaptive cruise control system based on model predictive control(MPC),and proposes a variable weight coefficient method to meet the driving requirements of different working conditions.And multi-mode ACC system is also studied.Because the direct control structure will affect the robustness of the system,this paper uses hierarchical control scheme to complete the design of car-following system.For the upper controller,it is necessary to consider many targets in the process of vehicle driving,including tracking,safety,comfort and fuel economy,as well as various constraints existing in the actual vehicle.Therefore,the model predictive control method which can effectively deal with multi-objective and system constraints is selected.For the lower controller,the actual acceleration is required to track the expected value quickly.Therefore,the feed forward plus feedback control method is used to eliminate the influence of non-linearity in the system.The PID control algorithm is used in the feedback control,which can meet the requirements of the system’s rapidity.In order to improve the adaptability of ACC system to the environment,a method of variable weight coefficient is proposed in this paper.According to different driving conditions,the weight coefficients of car-following and comfort in objective function are identified on-line by using fuzzy theory to achieve different emphasis on the two under different working conditions.Because the real road environment information is complex and changeable,this paper also studies the multi-mode ACC system.Firstly,according to the different emergency degree of vehicles,the driving conditions are divided into five different modes: cruise,accelerated approach,steady-state follow,decelerated approach and emergency follow.For each mode,the weight coefficients in the objective function and the corresponding constraints are re-adjusted to complete the design of the controller in each mode.The two control schemes are compared and analyzed,and the superiority of the multi-mode control scheme is verified.This paper takes Chang’an test vehicle as the target vehicle,car ACC system as the research object,vehicle dynamics simulation software Carsim and Simulink as the simulation experimental platform,builds the longitudinal motion control model of intelligent vehicle based on vehicle kinematics,and designs a more efficient and stable longitudinal control algorithm based on model predictive control,which can adapt to full speed conditions and meet vehicle multiple targets such as the safety,performance of following vehicle,performances of ride comfort and fuel economy.In order to verify the reliability of the control system,several groups of off-line simulation validation and real vehicle validation are carried out for five typical traffic scenarios.The results show that the multi-mode ACC system based on MPC control algorithm designed in this paper has better tracking effect.At the same time,the vehicle can take into account multiple driving objectives such as safety and comfort,and the vehicle state is smooth.Under extreme conditions,multi-mode ACC system can avoid collision accidents by emergency braking,thus expanding the scope of application of ACC system. |
