Analysis And Design Of Linear Controllers For Nonlinear Processes

How 'nonlinear' a nonlinear system can be and whether a linear controller is sufficient for a nonlinear process are basic problems for nonlinear control.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.For a typical nonlinear U-tube steam generator,a feedforward feedback control system is studied via static gain and gap metric method.The simulation results show the effectiveness of the proposed method.