IMPROVED MULTILOOP SINGLE-INPUT SINGLE-OUTPUT (SISO) CONTROLLERS FOR MULTIVARIABLE PROCESSES

Three methods are proposed for improving the performance of multiloop single-input/single-output (SISO) controllers which have been tuned by an approach illustrated in an earlier paper. In that paper, multiloop PI controllers were designed by detuning the controllers equally from SISO Ziegler-Nichols settings until a multivariable stability criterion was satisfied. In the present paper, several methods are described for adding derivative action to the PI controllers. An empirical procedure is developed for weighting the detuning of the loops by the predicted final ITE of the process after load and set-point disturbances.