Identification of low-order process model with time delay from closed-loop step test

To facilitate control-oriented model identification during closed-loop system operation, a low-order model identification method is proposed in this paper, based on using closed-loop step response test. By introducing a damping factor to the closed-loop step response for realization of the Laplace transform, a frequency response estimation algorithm is developed in terms of the closed-loop control structure used for identification. Correspondingly, two model identification algorithms are derived analytically for obtaining the widely used low-order process models of first-order-plus-dead-time (FOPDT) and second-order-plus-dead-time (SOPDT), respectively. Illustrative examples from the recent literature are given to demonstrate the effectiveness of the proposed identification algorithms.