Study on Coordinated Control Strategy of Electric Vehicle AFS and DYC Based on Phase Plane Method

In order to improve the path tracking ability and dynamic stability of a four in-wheel-motors drive electric vehicle, the dynamic models of the vehicle are built and the boundary of the dynamic stability range is determined by using phase plane method. Then, the layered control structure is adopted for designing a control system. The upper layer controller adopts the extension coordination control method to determine the weights of the active front-wheel steering (AFS) controller and the direct yaw-moment controller (DYC). The middle layer controller uses the nonlinear triple-step control method to calculate the additional front-wheel angle and the additional yaw-moment required by the vehicle. The switching control of the active front-wheel steering controller and the direct yaw-moment controller is realized according to the dynamic stability and riding state of the vehicle. At the lower layer controller, two signals obtained by the upper layer controller are used to optimize the four driving motor torques based on the quadratic programming method. These signals are the additional front-wheel angle and additional yaw-moment, and they are delivered to the steering motor and four driving in-wheel-motors. The model and controller of the in-wheel-motor driving vehicle are built by CarSim and MATLAB/Simulink software, and the simulation analysis is carried out under the double-lane change condition. The results show that the proposed vehicle controller strategy can improve the path tracking ability and the dynamic stability of the whole vehicle. And the riding vibration of the electric vehicle is also improved.