| Distributed drive electric vehicles have the advantages of high control flexibility,short transmission chain,high efficiency,and high space utilization.These advantages provide a broad prospect for improving drive efficiency,tapping vehicle control potential,and improving vehicle safety,and also provide an outstanding platform for autonomous driving technology.The development of intelligent distributed drive electric vehicles has become an important way to address traffic safety and environmental issues.Therefore,this paper researches the trajectory tracking control and yaw stability control methods of distributed drive electric vehicles.A hierarchical control architecture is proposed,including an upper-level motion controller and a lower-level torque distribution controller.Based on reasonable assumptions,a 7-degree-of-freedom nonlinear vehicle dynamic model including vehicle longitudinal motion,lateral motion,yaw motion and rotation of four wheels is developed.The motor parameters are matched according to vehicle parameters and vehicle dynamic performance indexes.In the upper-level controller,a trajectory tracking and yaw stability controller based on linear time-varying model predictive control is established with the consideration of longitudinal and lateral coupling.First,the nonlinear vehicle dynamic model is transformed into linear model by local linearization.Then a multi-objective optimization function considering trajectory tracking accuracy,yaw stability,and power performance is proposed.The soft constraint of tire side slip angle is applied to avoid lateral force saturation.Through the online optimization,control inpus-front wheel steering angle,traction force,and additional yaw moment-are obtained.In the lower-level controller,a torque distribution controller based on nonlinear model predictive control is brought forward to alloate traction force and additional yaw moment gotten by the upper-level controller.A nonlinear dynamic system with the consideration of varing tire longitudinal stiffness is constructed.The objective function containing the constraint of tire slip ratio and motor energy saving is designed.To reduce computational complexity,using a cubic polynomial to fit the power loss function.The varing constraint on motor torque is achieved by considering motor external characteristic and road adhesion.The torque distribution control of redundant motor actuators is achieved by solving the optimization problem.Carsim/Simulink joint simulation results under typical working conditions illustrate that,at high speed and low adhesion conditions,the proposed method could achieve favorable trajectory tracking effect while ensuring yaw stability,and good acceleration performance while preventing wheel slip,as well as improving energy economy.In addition,the real-time experiment results,based on NI Veri StandSimulink-CarSim,demonstrate that the upper-level controller could work in real time. |
