Active Safety Control Strategy For Electric Vehicle Of Redundant Actuator

Wire steering and wheel motor technology have brought new space for thedevelopment of electric vehicle.Four-wheel-independent-drive and four-wheel-independent-steering can greatly enhance the dynamic performance of the vehicle. However, since thesystem has more actuators than controlled objects, it may has the redundant problem whichmakes the traditional chassis control methods difficult to adapt. With the funding ofShenyang science project (F12-277-1-11) of “The Key Technology of Doubly-Fed Motor,AWD, Differential, Handling and Stability Control of Electric Vehicle”, according to thefeatures of the redundant actuator, electric vehicle active control safety system has beenresearched and designed.Firstly,4WIS-4WID electric vehicle model is built on Matlab/Simulink platformwhich includes tire, driving, braking and steering models. Compared with standard modelof vehicle dynamic simulation software Carsim, the validity of electric vehicle model isverified.Secondly, the limitation of front-wheel-steering vehicle model is analyzed. Accordingto the features of4WIS-4WID vehicle with redundant actuator, an electric vehicle activesafety control system of redundant actuators is designed. The system adopts a hierarchicalstructure coordinates with road adhesion coefficient feedback. When tracking the intensionof the driver, it can implement necessary interventions under special or emergencycondition.The upper level is consisted by the driver intension identification model and thevehicle dynamic controllers. Based on the two degrees ideal vehicle model，driver input isconverted into longitudinal velocity, lateral velocity and yaw angle by vehicle dynamicscontroller. And through the nonlinear system exact linearization and feedforwardcompensation, vehicle dynamics controller generates longitudinal force, lateral force andyaw moment. The lower level is the tire-force distribution controller. Four longitudinal andlateral forces is assigned by tire force distribution controller using quadratic programmingapproach to minimize tracking error of vehicle dynamics controller output and actuator output with polygonal approximating tire friction circle as its constraint. Meanwhile,since the characteristics that wheel motor torque are measurable, the problem ofidentification of road adhesion coefficient is solved while controlling the tire force.Finally, the control system has been improved under two failure conditions. In highspeed and large steering conditions, the interference elimination objective function of thetire force is employed which makes the tire force utilization achieve the best. When anactuator fails to work, through fault evaluation and system reconfiguration, make thesystem control of the vehicle effective again. The effectiveness of the algorithm isdemonstrated by simulation.