A Positive Observer for Linear Systems

We develop a positive observer for general (i.e. non necessarily positive) linear time varying systems, in both the continuous and discrete time cases. A nice feature of the approach is that no change of coordinates is needed. The observer size is twice the size of the observed system and it is stable whenever the observed system is stable. The design is based on a stable internally positive representation of linear systems that is also an original contribution of the paper. This positive observer can be used to develop interval observers and controllers for systems with several kinds of uncertainties.