Observer synthesis of nonlinear interconnected systems by constrained Riccati approach

This paper provides a method for observer synthesis of interconnected systems with nonlinearities in subsystems and interconnection terms, which satisfy the Lipschitz-type conditions instead of any matching conditions. A new observer scheme is proposed under a local observability assumption, and the respective observer gains are obtained through Riccati equations with linear constraints. Solvability conditions for such a Constrained Riccati Problem (CRP) are derived, and a systematic procedure for obtaining the solution of a constrained Riccati equation is presented. Furthermore, the relationship between tolerable Lipschitz constants of the modeling nonlinearities and observer gains is established.