Partial observability normal form for nonlinear functional observers design

In this paper, we investigate Partial Observability Normal Forms (PONF) of nonlinear dynamical systems. Necessary and sufficient conditions for the existence of a diffeomorphism bringing the original nonlinear system into a PONF are established. This enables us to estimate a part of state of a nonlinear dynamical system. A concrete example (SIR epidemic model) is provided to illustrate the feasibility of the proposed results.