Browsing by Author "Ahmed, Saeed"
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Item Open Access Distributed output feedback control of decomposable LPV systems with delay and switching topology: application to consensus problem in multi-agent systems(Taylor & Francis, 2020-01-08) Zakwan, Muhammad; Ahmed, SaeedThis paper presents distributed output feedback control of a class of distributed linear parameter varying systems with switching topology and parameter varying time delay. To formulate the synthesis conditions for the distributed controller in terms of LMIs, the delay dependent bounded-real lemma based on parameter-dependent Lyapunov–Krasovskii functionals is used. The efficacy of the result is illustrated by applying it to two real-world examples pertaining to the consensus problem of multi-agent systems.Item Open Access Distributed output feedback control of decomposable lpv systems with delay: application to multi-agent nonholonomic systems(IEEE, 2019) Zakwan, Muhammad; Ahmed, SaeedThis paper presents distributed output feedback control of a class of distributed linear parameter varying systems with a parameter-dependent time-varying delay. A delaydependent bounded-real lemma approach, based on parameterdependent Lyapunov-Krasovskii functionals, is used to formulate the synthesis condition in terms of linear matrix inequalities. We demonstrate the efficacy of our result by applying it to formation control of multi-agent nonholonomic mobile robots.Item Open Access Dynamic output feedback stabilization of switched linear systems with delay via a trajectory based approach(Elsevier, 2018) Ahmed, Saeed; Mazenc, F.; Özbay, HitayA new technique is proposed to construct observers and to achieve output feedback stabilization of a class of continuous-time switched linear systems with a time-varying delay in the output. The delay is a piecewise continuous bounded function of time and no constraint is imposed on the delay derivative. For stability analysis, an extension of a recent trajectory based approach is used; this is fundamentally different from classical Lyapunov function based methods. A stability condition is given in terms of the upper bound on the time-varying delay to ensure global uniform exponential stability of the switched feedback system. The main result applies in cases where some of the subsystems of the switched system are not stabilizable and not detectable.Item Open Access Finite time estimation for time-varying systems with delay in the measurements(Elsevier, 2019) Ahmed, Saeed; Malisoff, M.; Mazenc, F.We build finite time observers for time-varying nonlinear systems with delays in the outputs, using a dynamic extension that computes fundamental matrices. Our observers achieve finite time convergence when no disturbances are present. When disturbances are present, we provide approximate values for the solutions, which lead to an upper bound on the approximation error after a suitable finite time. We illustrate our work in a class of systems arising in the study of vibrating membranes, where time-varying coefficients can be used to represent intermittent measurements.Item Open Access Observer design and output feedback Stabilization of time varying systems(Bilkent University, 2018-07) Ahmed, SaeedWe study observer design and output feedback stabilization of switched and nonlinear time varying systems. To establish the stability of feedback switched systems with delay, we develop a new extension of a recently proposed trajectory based approach which is fundamentally different from classical Lyapunov function based methods. This new extension of trajectory based approach, which is of interest for its own sake, can be applied to a wide range of time varying systems with time varying delays and it tackles the issue of finding appropriate Lyapunov functions to establish stability results. Our stabilization methodology does not require stabilizability and detectability of all of the subsystems of the switched system and we do not impose any constraint on the derivative of the time varying delay. For nonlinear time varying systems, we build a new type of finite-time smooth observer in the case where a state dependent disturbance affects the linear approximation. We combine this finite time observer design and a switched systems approach to develop stabilizing feedbacks for nonlinear time varying systems whose outputs are only available on some finite time intervals. Again, we use an extension of the trajectory based approach to conclude the stability of the closed-loop system. Motivated by the fact that the measured components of the state do not need to be estimated, we also construct reduced order finite time observers for a broad class of nonlinear time varying systems. We show how these reduced order finite time observers can be used to solve dynamic output feedback stabilization problem for multiple input, multiple output nonlinear time varying systems. Finally, we design a finite time observer to estimate the exact state of a continuous-time linear time varying system from sampled output in the presence of a piecewise continuous disturbance.Item Open Access Output feedback stabilization by reduced order finite time observers using a trajectory based approach(IEEE, 2019) Malisoff, M.; Mazenc, F.; Ahmed, SaeedWe use finite time reduced order continuous-discrete observers to solve an output feedback stabilization problem for a class of nonlinear time-varying systems whose outputs contain uncertainty. Unlike earlier works, our feedback is discontinuous, but it does not contain distributed control terms. Our trajectory based approach is based on a contractivity condition. We illustrate our control in the context of a tracking problem for nonholonomic systems in chained form.Item Open Access Reduced order finite time observers for time-varying nonlinear systems(Institute of Electrical and Electronics Engineers Inc., 2019) Mazenc, F.; Ahmed, Saeed; Malisoff, M.; Teel, A. R.; Egerstedt, M.We build reduced order finite time observers for a large class of nonlinear time-varying continuous-time systems. We illustrate our results using a tracking problem for nonholonomic systems in chained form.Item Open Access State feedback stabilization of switched systems with delay: trajectory based approach(IEEE, 2017) Mazenc, F.; Ahmed, Saeed; Özbay, HitayWe present a new trajectory based approach for state feedback stabilization of switched linear continuous-time systems with a time-varying input delay. In contrast with finding classical common Lyapunov function or multiple Lyapunov functions for establishing the stability of the closed-loop switched system, the new trajectory based approach relies on verifying certain inequalities along the solution of a supplementary system. This study does not make any assumption regarding the stabilizability of all of the constituent subsystems of the switched system. Moreover, no assumption is needed about the differentiability of the delay and no constraint is imposed on the upper bound of the delay derivative. Finally, an illustrative example is included to illustrate the applicability of our results.