The Rational Transfer Function of a Discrete Control System and Its Linear Quadratic Controllers

A rational function for the transfer function model of a multivariable discrete control system is suggested and its controllers are obtained. There are two types of control systems depending on the nature of the disturbance. For tracking control systems, the disturbance is a set of set point changes. For regulating control systems, the disturbance is a vector ARIMA time series. The quadratic performance controllers for these systems are similar but opposite in nature. For tracking control systems, a two and a half degrees of freedom controller can be designed for an enhanced quadratic performance. This controller uses the future values of the disturbance which are the set points of the control system for further reduction of the error. The controller is particularly useful for nonminimum phase tracking control systems.