Identification of delay dominant recycle systems

A new identification method for single-input–single-output delay dominant recycle systems is presented in this paper. Identification of recycle systems is similar to that of closed loop systems. However, identification of recycle systems poses certain challenges in that the input-equivalent signal in the closed loop identification is not available for recycle systems. Therefore, special identification routines are required to ensure consistency of recycle and forward models. It is shown that consistent estimates of delay dominant recycle systems can be obtained by treating a delayed output as one of the inputs. Asymptotic variance expressions for the estimates of forward and recycle models are provided. These are then used in designing an optimal excitation signal for recycle systems. The results are illustrated through an industrial example.