Finite- and Fixed-Time Nonovershooting Stabilizers and Safety Filters by Homogeneous Feedback

TL;DR

This paper introduces homogeneous feedback laws for fixed-time non-overshooting stabilization of nonlinear systems, enabling safety filters that keep systems within safe sets and reach boundaries within a user-defined fixed time.

Contribution

It develops novel homogeneous feedback laws for fixed-time non-overshooting stabilization and safety filtering in nonlinear systems with full relative degree.

Findings

Homogeneous feedback laws achieve fixed-time stabilization.

Safety filters ensure system safety within a fixed time.

Applicable to nonlinear systems diffeomorphic to chains of integrators.

Abstract

Non-overshooting stabilization is a form of safe control where the setpoint chosen by the user is at the boundary of the safe set. Exponential non-overshooting stabilization, including suitable extensions to systems with deterministic and stochastic disturbances, has been solved by the second author and his coauthors. In this paper we develop homogeneous feedback laws for fixed-time nonovershooting stabilization for nonlinear systems that are input-output linearizable with a full relative degree, i.e., for systems that are diffeomorphically equivalent to the chain of integrators. These homogeneous feedback laws can also assume the secondary role of `fixed-time safety filters' (FxTSf filters) which keep the system within the closed safe set for all time but, in the case where the user's nominal control commands approach to the unsafe set, allow the system to reach the boundary of the safe set no later than a desired time that is independent of nominal control and independent of the value of the state at the time the nominal control begins to be overridden.