Design of cascade controllers for zero assignment in multivariable systems†

Abstract

The paper describes a method for the design of a constant cascade controller to assign some zeros and numerator coefficients of the (open or closed-loop) transfer function matrix of a linear multivariable system. The cascade controller does not affect the poles of the system which can be positioned prior to the zero assignment. The requirements on the transfer function matrix for arbitrary assignment of some zeros and numerator coefficients are discussed. The cascade controller is calculated from sets of simple linear equations and thus the method is computationally very efficient. An interactive computer programme is described for the computer-aided design of cascade controllers. Finally, two simple numerical examples of zero assignment in open-loop and closed-loop systems are worked out in detail to illustrate the method.