Research On Adaptive Cruise Control Of Electric Vehicle

With the rapid developments of global economy and automobile electronic technology,the production and sales of automobiles increase fastly in domestic market,which,however,has brought a series of social problems such as traffic congestion,frequent traffic accidents,serious environmental pollution and a sharp growth of energy consumption.In order to solve these problems,electric vehicles and the active safety technology have become the trend of automobile technology.As Safety Driving Assist technology,adaptive cruise control(ACC)is an important component of vehicle active safety technology and has been widely studied both at home and abroad.However,current research on adaptive cruise system mainly focuse on fuel vehicles instead of electric vehicles.Moreover,the study of adaptive cruise system also varies with the vehicle power system,therefore this thesis has great practical significance and value with study of adaptive cruise system based on electric vehicles.In this paper,control algorithms of adaptive cruise control system for electric vehicles are studied under different working conditions and hierarchies.The control system is divided into two levels: decision level and execution level.The decision level includes three modes,tracking control,speed control and uniform speed control to adapt to different driving environment of ACC vehicles.The execution level designs a drive controller and a brake controller to achieve the tracking control of desired accelerations exported by the decision level.Firstly,a model of control object is established in the tracking control mode of the decision level,whose task is to keep the actual distance between ACC vehicle and the target vehicle tracking the desired distance.First of all,a vehicle safety distance planning strategy is selected to plan the safety vehicle distance between the ACC vehicle and the target vehicle.When the vehicle enters a curve,information of radial relative motion obtained from the radar is required to be converted to the longitudinal information.Finally,only considering the longitudinal control of ACC system,the linear parameter varying model of distance error is established,which combine longitudinal kinematic characteristics and expected safety distance between the ACC vehicle and the target vehicle.Secondly,the control strategy of the decision level of ACC system is designed,including control modes under different working conditions and the controller switching strategy to realize smooth switch amoung controllers.In the distance control mode,as parameters of the proposed LPV model is measurable and bounded,the distance controller can be designed using Hinf control algorithms.In the speed control mode,the PID control algorithm is used to design the cruise control controller to realize speed tracking.Finally,a driving controller and a braking controller of the execution level are established to track the desired acceleration.Since electric vehicles can control the wheel torque precisely,it is possible to control the driveing and braking process by wheel torque.While building the longitudinal drive dynamic model and the braking dynamic model of the ACC vehicle,the influence of wheel slip rate and shaft load transfer are taken into account,and the controller can be designed by using the sliding mode control algorithm because of the strong nonlinearity of the model built.Then high precision simulation software veDYNA is used to perform the simulation under different scenarios to verify the performance of the ACC control system composed of the controllers of decision layer and the execution layer.The scenarios include the target vehicle decelerates scenario,the target vehicle decelerates first and then accelerates scenario,the target vehicle brakes scenario as well as the adjacent lane vehicle insertion scenario.The simulation results show that the algorithm has good performance and strong robustness.