Adaptive Constraint-Lifting Control with Stability and Invariance Guarantees

Abstract: This paper develops an adaptive tracking controller for a class of nonlinear systems with parametric uncertainty subject to state constraints. The system is characterized by a strict-feedback structure with unknown parameters entering both the drift and input channels. The objective is to design a control law, without knowledge of the unknown parameters, that guarantees closed-loop stability, achieves desired tracking performance, and ensures forward invariance of a prescribed safe set. An adaptive constraint-lifting framework is developed that transforms the constrained control problem into an equivalent unconstrained representation, enabling recursive controller synthesis in lifted coordinates. The proposed design integrates parameter estimation with constraint enforcement without requiring online optimization. A Lyapunov-based stability analysis, combined with the Barbashin-Krasovskii-LaSalle invariance principle, establishes boundedness of all closed-loop signals, asymptotic convergence of the system states to the desired equilibrium, and forward invariance of the safe set under uncertainty. In particular, the analysis characterizes the largest invariant set of the closed-loop system and guarantees convergence despite unknown parameters. The effectiveness of the proposed approach is demonstrated on a DC motor system with uncertain parameters, illustrating accurate tracking performance and safe operation.