New conditions for annular finite-time stability of linear systems

In this paper we investigate the annular finite-time stability (AFTS) problem for linear systems. A system is said to be annular finite-time stable if the norm of the system state remains within an upper and lower treshold for a given finite interval of time. Two necessary and sufficient conditions are provided for AFTS, the former requiring the solution of a differential Lyapunov equation (DLE), the latter involving an optimization feasibility problem constrained by differential linear matrix inequalities (DLMIs). We show that the DLE-based condition is more efficient from the computational point of view; however the DLMI-based condition is the starting point to investigate the design problem. To this regard a necessary and sufficient condition for the existence of a state feedback controller which renders the closed loop annular finite-time stable is provided. A numerical example illustrates the improvement of the proposed approach with respect to those existing literature