Nonlinearity measure based on disturbance rejection

In order to check whether a linear controller is sufficient for a nonlinear process, a control-relevant nonlinearity measure is defined in this paper. The measure is based on the variation of the disturbance rejection performance at the whole operating range for a fixed linear controller. It is simple to compute and can show where the process is most nonlinear or linear. Examples show that the measure can obtain more accurate process nonlinearity information than that given by the gap metric.