A Joint Input-Output Approach to Closed-loop Identification of Hammerstein-Wiener Systems

Abstract

This paper deals with a joint input-output method of identifying a closed-loop Hammerstein-Wiener system, where a linear plant in the forward loop may be unstable. A model that simulates the closed-loop system is derived using basis function expansions of nonlinearities. First, a linear state-space model of the forward loop is identified using Two-stage ORT method [12] 1. Then, initialized by the identified state-space model and linear approximations of nonlinearities, the joint input-output mean square error (MSE) is optimized by using the robust gradient method [20]; the identification algorithm yields good numerical results within moderate computation time.

Analysis of low-frequency vibration in a steam turbine based on closed-loop system identification

“…The proposed method is based on a direct method of closed-loop system identification. There are other system identification methods: indirect, two-stage, and joint input-output methods (Prasad et al, 1977, Linder and Enqvist, 2017, Ase and Katayama, 2018). These methods use information from the feedback controller or the input data for the closed-loop system.…”