Full Closed-Loop Tests for the Relay Feedback Autotuning of Stable, Integrating, and Unstable Processes

Jietae Lee; Su Whan Sung; Friedrich Y Lee; Michael Baldea; Thomas F Edgar

doi:10.1021/acsomega.9b02732

Full Closed-Loop Tests for the Relay Feedback Autotuning of Stable, Integrating, and Unstable Processes

ACS Omega. 2019 Oct 30;4(20):18760-18770. doi: 10.1021/acsomega.9b02732. eCollection 2019 Nov 12.

Authors

Jietae Lee¹, Su Whan Sung¹, Friedrich Y Lee², Michael Baldea², Thomas F Edgar²

Affiliations

¹ Department of Chemical Engineering, Kyungpook National University, Daegu 702-701, Korea.
² Department of Chemical Engineering, University of Texas, Austin, Texas 78712, United States.

Abstract

The relay (on-off) controller can stabilize wide ranges of processes including open-loop stable, integrating, and unstable processes, producing sustained oscillations. For improved proportional-integral-derivative controller tunings, methods to find process models with mixed closed-loop tests of relay feedback and proportional-derivative (PD) controllers are proposed. For unknown processes with arbitrary initial states, relay feedback tests are first applied and, after cyclic steady states are obtained, PD controllers or other relay feedback tests with set point changes are followed. This full closed-loop operation is desirable for integrating and unstable processes and will be useful even for stable processes when processes are far from their desirable operating points. Refined methods to find exact frequency responses of processes from initial and final cyclic steady states are derived. Whole relay feedback responses need not be saved. Several integrals at the relay switching times are used without iterative tests or computations.