Relay-Based Autotuning of PID Controller for Improved Load Disturbance Rejection

To overcome sluggish load disturbance response for industrial/chemical processes with slow time constant (s), an improved design for on-line autotuning of proportional-integral-derivative (PID) controller is proposed in this paper, based on relay identification of the widely used first-order-plus-dead-time (FOPDT) process model. Using the fitting conditions established for process response at the oscillation frequency under a relay test, the identification algorithm is transparently developed. An analytical controller tuning method is then developed using an asymptotic constraint established thereby for reducing the influence of the slow process time constant on load disturbance rejection. Illustrative examples are given to show the effectiveness and merits of the proposed algorithms. Copyright © 2007 International Federation of Automatic Control All Rights Reserved