Projection Method in Closed Loop System Identiication R E Gl Ertek N Ik a U T O M at Ic Co N T R O L Projection Method in Closed Loop System Identiication

Technical reports from the Automatic Control group in Linkping are available by anonymous ftp at the address ftp.control.isy.liu.se. This report is contained in the compressed postscript le 2026.ps.Z. Abstract This paper deals with a new method for closed loop identiication, i.e. the projection method. This method generalizes the already known two-stage method by allowing the estimation of non-causal closed loop sensitivity models in its rst step. Such models have been shown to lead to robust identiication (as the second step) of the open-loop system dynamics in the presence of marginal nonlinear closed loop behaviors. This robustness property is investigated. It results a simple \rule of thumb" under which the innuence of these closed loop nonlinearities on the open-loop model estimate remains small.