Abstract
Descriptor equations have much more flexibility in describing nonlinear systems than state equations. In this paper, based on the Lyapunov's direct method, stability conditions are developed for nonlinear descriptor systems. An existence condition of solutions of descriptor equations is also derived. The results remove the differentiability assumptions on nonlinearities in descriptor equations, which are required in the existing works. As an application of the conditions, stability analysis of a Lur'e-type feedback system whose linear part has a direct path is considered by using a descriptor expression.
