Should the desired vehicle heading in path following of autonomous vehicles be the tangent direction of the desired path?

The path following problem for autonomous vehicles (AVs) is investigated in this paper. The desired value of the vehicle heading is commonly chosen as the tangent direction at the orthogonal projection point of vehicle CG (center of gravity) on the desired path. This paper points out that the traditional definition of the desired heading may deteriorate the path following performance, especially when the vehicle is tracking a path with large curvature. That is because the sideslip angle control and the yaw rate control are conflicting in the presence of sliding effects, and the sideslip angle cannot equal to zero when vehicle is tracking a curve path. This paper further provides an amendment to the definition of the desired heading direction, which renders the path following objective realized more accurately. In the controller design phase, backstepping is used to generate the required yaw rate, which has a form of the P controller, then an LQR controller is adopted to obtain the optimal active front steering (AFS) input. The Carsim-Simulink joint simulation verifies the reasonability of the amendment to the heading error.