Lyapunov stability analysis of an RMRAC-based adaptive sigmoid super-twisting sliding mode under matched and unmatched uncertainties

This article presents a discrete-time robust model reference adaptive controller and adaptive sigmoid super-twisting sliding mode (RMRAC-ASSTSM) and its stability analysis using Lyapunov stability theory. This control structure is robust to matched and unmatched dynamics. In addition, the chattering phenomenon tends to be suppressed in the steady state due to adaptive super-twisting sliding mode action using a sigmoid function. The performance of the proposed control structure is corroborated with simulation results, considering a second-order non-minimum phase unstable plant, where it can be seen that RMRAC-ASSTSM regulation errors converge to a finite residual set when the plant presents unmodeled dynamics. A comparison is also presented with a similar RMRAC-based control structure with an adaptive super-twisting sliding mode implemented with a sign function.