Discussion on: 'On Observability and Pseudo State Estimation of Fractional Order Systems'

摘要

In this paper, the authors raised an important issue concerning the interpretation of a fractional order state space model and the exact definition of the notion of state for fractional order systems. A reformulation of the model which highlights the infinite dimensional character of the system is proposed. Based on this reformulation, the observability property is studied. It has been shown in the paper under discussion that a fractional order system is not exactly observable but only approximately observable. This statement is true if the output function is taken as a linear combination of state variables. In the present discussion, we propose an alternative view on this issue. By defining an appropriate output function that takes into account the long memory aspect of the system, we have shown that a fractional order system can be completely observable.