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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 43814 (05)
- University: Sharif University of Technology
- Department: Electrical Engineering
- Advisor(s): Nobakhti, Amin
- Abstract:
- Integrity of closed-loop systems with integral action control is characterized by using a series of successively more difficult to obtain conditions: Integral Stabilizable (IS), Integral Controllable (IC), Integral Controllable with Integrity (ICI), and Decentralized Integral Controllability (DIC). The IS condition requires that for a Linear Time-Invariant (LTI) finitedimensional (FD) plant, G(s), one finds a stabilizing decentralized controller with integral action. For G(s) to be IC, in addition to being IS, one should be able to reduce the gain of
all control loops by the same factor from a finite value to (but not including) zero without introducing instabilities. ICI requires that in addition to G(s) being IC, the closed-loop system will remain stable if any loops are taken in or out of service. The ultimate condition is DIC which requires that the system be ICI and any independent adjustment of the gain of each loop in a finite interval (including zero) does not introduce instabilities. A key point is that the integrity of a closed-loop system is a property of the system (and not the controller) and may be altered by a change in the order in which the inputs and outputs are paired. A fundamental assumption in the present framework for the study of system integrity is that the system under consideration is finite dimensional (FD). This poses difficulties when there are delays present in the system inputs, outputs and states. In reality these types of delays are almost always present. In interconnected process systems, it is often the case that the states of one subsystem are the outputs of another. This will cause delay terms to appear in the states of the corresponding state-space model. The previous work reviewed above, do not present a theoretical basis for the treatment of non-FD time delay systems, even though examples of process systems with input-output time delays appear sparsely in the revelent literature. Using the ring-model description in terms of the delay operator for general LTI time-delay system (with delays in states, inputs or outputs), generalization of generalized Nyquist criterion for non-FD multivariable LTI time-delay systems and strong stabilizability, it is shown that the integrity conditions for IS, IC, ICI and DIC which have been developed previously, remain valid and carry over to non-FD time delay systems. That is, for such system, steady-state information remains the only information necessary and required to assess the closed-loop integrity under fully decentralized control with integral action. The importance of this contribution is in the fact that almost all process systems have time delays - Keywords:
- Integration ; Time Delay ; Decentralized Controller ; Ring-Model Description ; Decentralized Fixed Models (DFM) ; Strong Stability ; Integral Stabilizability (IS) ; Integral Controllability
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