Composite adaptive second-order nonsingular terminal sliding mode controller for path-tracking of general N-trailer systems

Path-tracking control of autonomous tractor-trailers systems (TTSs) is a challenging issue due to complex multi-body dynamics and underactuated features. Notably, varying numbers and configurations of trailers and environmental disturbances degrade the path-tracking performance of conventional control methods. To this end, we propose a composite adaptive second-order nonsingular terminal sliding mode (CASONTSM) controller for TTSs, applicable to both traditional and active trailer steering (ATS) configurations. The CASONTSM controller consists of three parts: a general dynamic model (GDM), an ASONTSM controller, and an adaptive extended state observer (AESO). The GDM can uniformly represent N-trailer systems with different types of hitching types and trailers; the AESO is designed to estimate and compensate for the lumped disturbances and suppress measurement noise; the ASONTSM controller ensures finite-time convergence by employing SONTSM manifold and simultaneously overcome the tradeoff between the transient response and the chattering phenomenon. By incorporating these three components, the CASONTSM can significantly improve tracking accuracy and robustness for traditional TTSs, while effectively reducing off-tracking effects for TTSs equipped with ATS. The practical finite-time stability of the path-tracking system is rigorously proved through Lyapunov theory. Finally, comparative simulations and real-world experiments validate the effectiveness and robustness of the proposed composite control method.