Minimum variance lower bound ratio based nonlinearity measure for closed loop systems

A nonlinearity measure based on minimum variance lower bound ratio is presented.This measure belongs to the data-driven class, and can be used for Hammerstein structure, Wiener structure and Wiener–Hammerstein structure.The effectiveness and consistency of this measure are illustrated by simulation tests and an industrial case.

Uninterrupted wide range operations are salient features of the process industries. Characteristics including nonlinearity, time-delay, and inertia, of industrial control loops are always significantly changed with the working conditions. To qualify the nonlinear degree, a nonlinearity measure based on the minimum variance lower bound ratio is presented in this paper. This measure belongs to the data-driven class, and can be applied to Hammerstein structure, Wiener structure and Wiener–Hammerstein structure, whether the controller is linear or nonlinear. The effectiveness and consistency of this measure are illustrated through five simulation tests. An industrial case in the fossil fuel power generation process is studied to confirm the practicability of the proposed measure.