Observability/detectability analysis for nonlinear systems with unknown inputs - application to biochemical processes

Determination of the observability/detectability properties of a nonlinear system is fundamental to assess the possibility of constructing observers and their expected properties as convergence assignability. For linear systems this task can be solved by well-known techniques, for the unperturbed and also the case with perturbations. However, for nonlinear systems this study is usually a very hard task, in particular when perturbations are present. In this paper a general method to study these properties will be described, and its capabilities and feasibility will be assessed by means of a few case studies related to the culture of phytoplankton in the chemostat.