Identification using single symmetrical relay feedback test

Using a single symmetric relay feedback test, a method is proposed to identify all the three parameters of a first order plus time delay (FOPTD) model. On identifying a higher order dynamics system by a FOPTD model, the conventional method identifies a negative time constant [Li, W., Eskinat, E., & Luyben, W. L. (1991). An improved auto tune identification method. Industrial and Engineering Chemistry Research, 30, 1530-1541] due to the error in neglecting higher order dynamics in the system output. In the present work, all the parameters of a FOPTD model are estimated with adequate accuracy. Three simulation examples are given. The estimated model parameters of a FOPTD model are compared with that obtained by Li et al. [Li, W., Eskinat, E., & Luyben, W. L. (1991). An improved auto tune identification method. Industrial and Engineering Chemistry Research, 30, 1530-1541] and also that with exact model parameters of the system. The performance of the controller designed on the identified model is compared with that identified by Li et al. [Li, W., Eskinat, E., & Luyben, W. L. (1991). An improved auto tune identification method. Industrial and Engineering Chemistry Research, 30, 1530-1541] and with that of the actual process. The proposed method gives performance close to that of the actual system. Simulation results for stable and unstable systems are given.