| The distributed drive vehicle has high power transmission efficiency and control freedom,and the wheels can respond to the driving instructions quickly and accurately to achieve the expected dynamic control effect.And for intelligent vehicle with distributed drive structure,the goal of trajectory tracking control is not only a precise tracking of reference trajectory plannd by the decision makers,but also to ensure the vehicle driving stability.For the trajectory tracking control problem of Distributed Driven Unmanned Ground Vehicle(DDUGV),a corresponding coordinated control algorithm is proposed in this paper,which mainly includes the following contents:(1)For the accuracy and stability of path following control under the condition of low adhesion,an improved model prediction controller is established.With the requirements of real-time performance and tracking accuracy of the algorithm,the influence of longitudinal motion on the tracking effect is considered.Specifically,the Jacobian matrix is obtained by taking wheel speed as non-state variant when linearizing the vehicle state equation in prediction horizon N_p so as to reduce the dimension of the system.The slip angle of vehicle is added into the performance index to modify the reference yaw angle,which can realize the convergence between position tracking error and angle tracking error from the perspective of vehicle dynamics.Finally,the position tracking error and angle tracking error are normalized dimensionless.(2)Combined with the unique driving structure of DDUGV,the fuzzy controller is used to adjust the PID parameters in real time to determine the total driving torque demand for speed control.With the speed tracking deviation and its rate of change as the input of the fuzzy controller,the appropriate fuzzy/clear conversion interface and domain conversion factor are designed to realize the organic combination of fuzzy control and PID.Simulation experiments are carried out on different road conditions,where the initial speed tracking error is limited,and both the low-speed of and high-speed reference are set as tracking targets.The results show that the designed controller has good speed tracking quality.(3)An improved SMC algorithm is used to realize yaw stability control of vehicle.Considering the dynamic effects of side slip angle and yaw rate,the switching surface function is designed.For the chattering phenomenon of SMC,the symbol function is replaced by a continuous function to improve the common exponential approach law so that the control system becomes a quasi-SMC.The DDUGV coordination control framework was established,and the dynamic demand of the vehicle tracking the reference trajectory is distributed to the four wheels as the driving torque according to the proportional distribution of the front and rear vertical loads.(4)Carsim-Simulink simulation platform was built to verify the proposed coordinated control strategy,and the results show that the controller has accurate and stable tracking ability. |
