Direct closed-loop identification approach to unstable systems

A new direct closed-loop identification method only using the plant input/output data acquired through an output inter-sampling scheme is presented in this paper. By taking the faster sampling of the system output than the control interval, we can clarify that the inter-sampled plant model can also be described by the SIMO model structure, which can provide the identifiability of the closed-loop. One of the advantages is that the proposed identification method using the inter-sampled output observations can remove the ordinary restrictive identifiability condition, and it is not required that the reference input holds the persistently exciting (PE) property. Its effectiveness is demonstrated through a numerical example.