Digital Control Design for Systems with Approximate Decentralized Fixed Modes

In this paper, the digital control of decentralized continuous-time systems, which have approximate decentralized fixed modes, is studied. It is shown that under some conditions, discrete-time controllers can improve the overall performance of the decentralized control system, when a linear time-invariant continuous-time controller is ineffective. In order to obtain these conditions, a quantitative measure for different types of fixed modes in a decentralized system is given. In this case, it is shown that generalized sampled-data hold functions (GSHF) instead of a simple zero-order hold (ZOH), in the implementation of the digital controllers, can significantly improve the overall performance of the resultant closed-loop system. The proposed sampled-data controller is, in fact, a linear time-varying controller for the continuous-time system