Hidden modes of interconnected systems in control design

A complete treatment of the hidden modes of interconnected systems in control design is presented that extends and unifies several results which have appeared in the literature in the past decades. The uncontrollable and/or unobservable hidden modes of one- and two-degree-of-freedom control systems are characterized in terms of transfer matrices of the interconnected subsystems and in terms of design parameters. This characterization leads directly to design conditions that can be used to control adequately the hidden modes, thus avoiding unnecessarily-high-order controllers and undesirable behavior. The methods are based on polynomial matrix internal descriptions. However, all results are expressed so that they can be directly used in control design. Internal stability is guaranteed using a novel stability theorem that adds significant insight to the problem. A method is also presented to characterize the hidden modes of any interconnected system.<
>