Browsing by Author "Niculescu, S.-I."

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Open Access
Comparing PI controllers for delay models of TCP/AQM networks
(Elsevier, 2010) Ünal H.U.; Melchor-Aguilar, D.; Üstebay, D.; Niculescu, S.-I.; Özbay, Hitay
In this paper, ns-2 simulations and related comparisons of four different PI controllers designed for TCP/AQM networks will be presented. The simulations are performed for various scenarios. © 2010 IFAC.
Open Access
Stability analysis of switched systems using Lyapunov-Krasovskii functionals
(Elsevier, 2011) Çalişkan, S.Y.; Özbay, Hitay; Niculescu, S.-I.
Piecewise Lyapunov-Razumikhin functions are previously used for obtaining a lower bound for the dwell time of the switched time delay systems under the assumption that each candidate system is delay dependently stable. In this work, using Lyapunov-Krasovskii functionals, a less conservative lower bound for the dwell time is obtained. Improvement in the dwell time is illustrated with an example. © 2011 IFAC.
Open Access
Stability windows and unstable root-loci for linear fractional time-delay systems
(Elsevier, 2011) Fioravanti, A.R.; Bonnet, C.; Özbay, Hitay; Niculescu, S.-I.
The main point of this paper is on the formulation of a numerical algorithm to find the location of all unstable poles, and therefore the characterization of the stability as a function of the delay, for a class of linear fractional-order neutral systems with multiple commensurate delays. We start by the asymptotic position of the chains of poles and conditions for their stability, for a small delay. When these conditions are met, we continue by means of the root continuity argument, and using a simple substitution, we can find all the locations where roots cross the imaginary axis. We can extend the method to provide the location of all unstable poles as a function of the delay. Before concluding, some examples are presented. © 2011 IFAC.