Abstract
Existence of fixed modes is not desirable for stabilization and pole assignment in linear time-invariant decentralized control sytems. Therefore, it is necessary to eliminate (undesirable) fixed modes by some methods.
In this paper, two methods are proposed for elimination of fixed modes of linear control systems with constrained control structures, typically including decentralized control structures. The methods make most use of the existent controllers and observers.
One method is addition of interconnection gains to the feedback structure. The minimal number of necessary additional interconnection gains and the positions to which they are added are made clear, based on the degrees of the fixed modes and the corresponding minimal effective subsystems.
The other method is addition of new control stations to the original system. The minimal total number of inputs and outputs necessary for elimination of undesirable fixed modes is provided, also based on the degrees of the fixed modes and the minimal effective subsystems. The proof shows how to construct new stations at the same time.
