An Outer Loop of Trajectory and an Inner Loop of Steering Angle for Trajectory Tracking Control of Automatic Lane Change System

Automatic Lane Change (ALC) function is an important step to promote the currently popular Advanced Driver Assistance Systems (ADAS) within a single lane. The key issue for ALC is accurate steering angle and trajectory tracking during the lane changing process. In this paper, an MPC controller with a receding horizon is designed to track the desired trajectory. During the tracking process, other objectives such as safety and smoothness are considered. Considering of the practical mechanism and parameter uncertainties, an SMC controller is designed to track the target steering angle. For validation, a Hardware-in-the-Loop (HIL) experiment platform is established, and experiments of different control algorithms under different conditions are carried out successively. Comparisons of the experiment results of MPC+SMC and PID+SMC schemes indicate that both the trajectory error and the steering angle error of the former combination are smaller. Specifically, the peak trajectory error in Y direction of MPC+SMC is by about 50% smaller under velocity from 60km/h to 80km/h, and lane change duration is also shorter than the PID+SMC scheme. And compared to the servo motor’s own position loop, the proposed SMC controller’s tracking performance is a little worse, but the angle tracking error is always within 0.01 rad. Given that the cost of a servo motor and the reality that most current EPS (Electric Power Steering) system does not equip a servo motor, the performance of the SMC controller here is acceptable. To make the results more convictive, several other experiments under different adhesion coefficients and prediction horizons were then carried out to show the robustness of the MPC+SMC scheme. All the results can support the conclusion that the proposed algorithm can fulfil the efficiency, comfortable, and safety requirements under different ALC conditions.