On steady-state based reduced-order observer design for interlaced nonlinear systems

This paper proposes an analytical expression for a nonlinear mapping between steady-state solutions of certain types of nonlinear interconnected systems. This mapping is found using tools from the theory of output regulation for systems presented in lower-triangular or upper-triangular canonical forms. Next, this mapping helps design an excitation input and a corresponding reduced-order observer for interlaced systems, a combination of both upper- and lower-triangular subsystems. A proposed global observer is proved to be robust to additive disturbance and measurement noise by applying the Lyapunov function method. An example involving a mass-spring system demonstrates the efficiency of our approach.