Reduced conservatism in testing for Hurwitz invariance of state-space models

This paper addresses the issue of ´conservatism´ in the time domain stability robustness bounds obtained by Lyapunov approach. A state transformation is employed to improve the upper bounds on the linear time-varying perturbation of an asymptotically stable linear time-invariant system for robust stability. This improvement is due to the variance of the conservatism of Lyapunov stability condition with respect to the basis of the vector space in which the Lyapunov function is constructed. Improved bounds are obtained, using transformation, on elemental and vector norm of perturbations (i.e., structured perturbations) as well as on matrix norm of perturbations (i.e. unstructured perturbations). For the case of diagonal transformation, an algorithm is proposed to find the ´optimal´ transformation. Several examples are presented to illustrate the proposed analysis.