Utilizing loop interaction in multivariable regulating systems

Presented in this paper is a controller design methodology for a class of square multivariable regulating systems that utilizes loop interaction to achieve output regulation of ill-specified systems. This is accomplished by designing off-diagonal controllers to donate control effort to loops that cannot meet their performance requirements. The class of performance specifications considered are actuator saturation limits and output tolerances. The proposed controller design methodology is a frequency domain approach based on sequential loop closure that incorporates all control elements of previously closed loops into subsequent loop designs. The design of the off-diagonal controllers takes advantage of this recursive technique by isolating the effects of each off-diagonal controller on subsequent loops. The restrictions on the class of multivariable systems are that it must be invertible and the inverted plant must be stable.