Direct closed-loop identification of unstable system by output inter-sampling scheme

A novel direct closed-loop identification method based on an output inter-sampling scheme is presented. By taking the faster sampling of the plant output than the control input, we can give a SIMO model representation. It is clarified that the SIMO structure can provide a new identification scheme to identify an unstable plant in closed-loop. One of the advantages is that the proposed identification method can remove the ordinary restrictive identifiability condition, and does not require that the reference input hold the persistently exciting (PE) property. Thus only one inter-sampling of the plant output can assure the identifiability of the plant parameters.