Hidden Modes of Two Degrees of Freedom Systems in Control Design

Panos J. Antsaklis and O.R. Gonzalez

Proceedings of the 1990 IEEE Transactions on Automatic Control
Vol. 35, No. 4, pp. 502-506, April 1990

Abstract - A complete treatment of the hidden modes of two degrees of freedom control systems is presented. The uncontrollable and/or unobservable hidden modes are characterized in terms of transfer matrices of the interconnected system and in terms of design parameters. This characterization leads directly to design conditions, which can be used to adequately control the hidden modes, thus avoiding unnecessarily high order controllers and undesirable behavior. Internal stability is guaranteed via a stability theorem which adds significant insight to the problem.

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