Independent parameterization of two-degree-of-freedom compensators in general robust tracking systems

Consideration is given to a general robust tracking problem in which the controlled object is a linear multivariable system having measured variables that are not necessary coincident with the output variables to be controlled. A necessary and sufficient condition for the two-degree-of-freedom compensator to achieve a robust tracking system with internal stability is given. An existence condition is derived for such a compensator, and the class of all such compensators is parameterized, so that two specifications with respect to responses for reference commands and feedback properties can be satisfied independently by the two free parameters