Wyniki wyszukiwania - BazTech

1

Fractional order PI controllers for TCP packet flow ensuring given modulus margins

Krajewski W., Viaro U.

Control and Cybernetics

|

2014

|

Vol. 43, no. 4

493--505

EN

An Active Queue Management (AQM) robust control strategy for Traffic Control Protocol (TCP) data transfer is proposed. To this purpose, the TCP behaviour is first approximated by a second–order model with delayed input obtained from the linearization of an efficient and commonly used nonlinear fluid–based model. The adopted feedback control structure uses a fractional– order PI controller. To ensure the desired robustness, the parameter regions where such a controller guarantees a given modulus margin (inverse of the H1 norm of the sensitivity function) are derived. An example commonly used in the literature is worked out to show that the suggested graphically–based design technique is simple to apply while it limits the effects of disturbances and of the unmodelled dynamics.

2

Iterative-interpolation algorithms for L2 model reduction

Krajewski W., Viaro U.

Control and Cybernetics

|

2009

|

Vol. 38, no 2

543-554

EN

This paper is concerned with the construction of reduced-order models for high-order linear systems in such a way that the L2 norm of the impulse-response error is minimized. Two convergent algorithms that draw on previous procedures presented by the same authors, are suggested: one refers to s-domain representations, the other to time-domain state-space representations. The algorithms are based on an iterative scheme that, at any step, satisfies certain interpolation constraints deriving from the optimality conditions. To make the algorithms suitable to the reduction of very large-scale systems, resort is made to Krylov subspaces and Arnoldi's method. The performance of the reduction algorithms is tested on two benchmark examples.

3

Remarks on the steady-state accuracy of a feedback control system

Ferrante A., Krajewski W., Lepschy A., Viaro U.

Control and Cybernetics

|

2000

|

Vol. 29, no 1

51-67

EN

The paper deals with the steady-state response of a feedback control system to the canonical inputs. For its characterization it seems useful to introduce the notion of accuracy index mi beside the standard notion of loop type v. This index is assumed to be equal to the power of t in the analytic expression of the canonical input that leads to a finite nonzero deviation between the actual and the desired responses. When applied in the control design procedure, the accuracy index mi allows to achieve a steady-state performance that is more satisfactory than the one obtainable with reference to the loop type only. The conditions under which a single-loop feedback control system exhibits a prescribed value of mi, given the value of v, are derived and discussed with particular regard to their robustness.