Relay Based Identification Scheme for Processes with Non-minimum Phase and Time Delay

This study presents the frequency-domain and state-space approaches for modelling and identification of processes exhibiting non-minimum phase and time delay characteristics. An asymmetrical relay is fed back to unknown process to bring sustained oscillatory responses or limit cycle at the process output. Utilising the relay settings and limit cycle information, a set of mathematical expressions for the identification of process dynamics in terms of non-minimum phase second-order plus time delay, non-minimum phase first-order plus time delay, non-minimum phase integrating first-order plus time delay models is deduced. As compared to the methods reported in recent literature, the proposed set of explicit expressions is completely free from the simultaneous solution of a set of non-linear equations and does not need any prior guess for initial value of the unknown process model parameters. Simulations of benchmark examples from literature and experimental results from coupled tanks system are included to demonstrate the efficacy of the proposed relay-based identification algorithms.