Steering rate controller based on curvature of trajectory for autonomous driving vehicles

We propose a steering control method for an autonomous vehicle by controlling the steering rate instead of the steering angle and describe a method for extracting the steering rate from the reference path using the relationship with curvature and slip angle. The proposed steering control method can be used not only for planning steering control input from the desired trajectories at the planning stage but also for the instantaneous planning of a driving path during vehicle motion. From the desired trajectory plotted in a two-dimensional XY coordinate system, the steering rate is extracted from the reference path, as a function of x. The extracted steering rate functions as the control input to the vehicle's controller for changing the front wheel's angle. MATLAB simulations of a double-lane-change maneuver were conducted for two scenarios, i.e., when the desired trajectory is given and when the driving path is planned instantaneously. For the double-lane-change maneuver, the curvature and the steering rate input to the controller are extracted from the virtually generated instantaneous reference path. The robustness of the proposed model and method are verified by re-constructing the trajectory traveled when the calculated steering rate is input into the controller.