Adaptive relay based identification and control of Hammerstein-type nonlinear processes

This paper presents a very simple and effective identification and control method for Hammerstein type nonlinear processes. Generally, a nonlinear process possessing static nonlinearity experiences an asymmetrical limit cycle output. During the relay feedback test, the relay height is adjusted such that the output becomes symmetrical. The static nonlinearity is identified from a single test and then its inverse function is used to nullify static nonlinearity in the process. Thereafter, a linear process model is identified and subsequently a linear PID controller is designed. Finally, the PID controller along with the inverse nonlinear function yields a simple nonlinear PID controller that is capable of controlling the nonlinear process effectively. The usefulness of proposed identification and control strategy is illustrated by two simulation examples.