Electrical and Electronic Engineering - Research Publications
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ItemStability properties of reset systems(Elsevier, 2005-01-01)Stability properties for a class of reset systems, such as systems containing a Clegg integrator, are investigated. We present Lyapunov based results for verifying L2 and exponential stability of reset systems. Our results generalize the available results in the literature and can be easily modified to cover Lp stability for arbitrary p ∈ [1;∞]. Several examples illustrate that introducing resets in a linear system may reduce the L2 gain if the reset controller parameters are carefully tuned.
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ItemNONLINEAR SAMPLED DATA CONTROLLER REDESIGN VIA LYAPUNOV FUNCTIONS(Elsevier BV, 2005)We provide results for redesign of Lyapunov function based continuous time controllers for sampled-data implementation, using a particular form of the redesigned controller and the Taylor expansion of the sampled-data Lyapunov difference. We develop two types of redesigned controllers that (i) make the lower order terms (in T) in the series expansion of the Lyapunov difference with the redesigned controller more negative and (ii) make the terms in the Taylor expansions of the Lyapunov difference for the sampled-data system with the redesigned controller behave as close as possible to the respective values of the continuous-time system with the original controller. Simulation studies illustrate the performance of our controllers.
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ItemNonlinear sampled-data observer design via approximate discrete-time models and emulation(Elsevier, 2005-01-01)We study observer design for sampled-data nonlinear systems using two approaches: (i) the observer is designed via an approximate discrete-time model of the plant; (ii) the observer is designed based on the continuous-time plant model and then discretized for sampled-data implementation (emulation). in each case we present Lyapunov conditions under which the observer design guarantees semiglobal practical convergence for the unknown exact discrete-time model. The semiglobal region of attraction is expanded by decreasing the sampling period. The practical convergence set is shrunk by decreasing either the sampling period, or a modelling parameter which refines the accuracy of the approximate model.
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ItemNetworked control systems: An emulation approach to controller design(Elsevier BV, 2007-01-01)We overview our recent work on a design approach for networked control systems (NCS) that resembles controller emulation for sampled-data systems. In the first step, we design a controller ignoring the network and, in the second step, we implement the designed controller over the network with sufficiently fast transmissions and a given protocol. Our results have several features: (i) they apply to general nonlinear systems with disturbances; (ii) we obtain explicit (often non-conservative) bounds on the maximal allowable transmission interval that guarantee stability; (iii) and we show that this approach is valid for a wide range of network scheduling protocols. This provides a flexible framework for design of NCS that is amenable to various extensions and modifications, such as a treatment of dropouts and stochastic protocols, combined controller/protocol design for linear plants, and so on.
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ItemA note on input-to-state stability of sampled-data nonlinear systems(IEEE, 1998)It is shown for nonlinear systems that sampling sufficiently fast an input-to-state stabilizing (ISS) continuous time control law results in an ISS sampled-data control law. Two main features of our approach are: we show how the nonlinear sampled-data system can be modeled by a functional differential equation (FDE); we exploit a Razumikhin type theorem for ISS of FDE that was recently proved in [14] to analyze the sampled-data system.
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ItemOutput stabilization of nonlinear systems: Linear systems with positive outputs as a case study(IEEE, 1998)The problem of stabilization of linear systems for which only the magnitudes of outputs are measured is studied. A stabilizing controller is constructed which is input to state stability (ISS)-robust with respect to observation noise. Modal analysis and theorems are presented to prove the stabilization properties of the controller.
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ItemOn uniform boundedness of parameterized discrete-time systems with decaying inputs: applications to cascades(ELSEVIER, 2003-07-05)A framework for controller design of sampled-data nonlinear systems via their approximate discrete-time models has been established recently. Within this framework naturally arises the need to investigate stability properties of parameterized discrete-time systems. Further results that guarantee appropriate stability of the parameterized family of discrete-time systems that is used within this framework have been also established for systems with cascaded structure. A fundamental condition that is required in this framework is uniform boundedness of solutions of the cascade. However, this is difficult to check in general. In this paper we provide a range of sufficient conditions for uniform boundedness that are easier to check. These results further contribute to the toolbox for controller design of sampled-data nonlinear systems via their approximate discrete-time models.
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ItemL-2 anti-windup for linear dead-time systems(ELSEVIER, 2005-12-01)In this paper, we address and solve the problem of anti-windup augmentation for linear systems with input and output delay. In particular, we give a formal definition of an optimal L2 gain based anti-windup design problem in the global, local, robust and nominal cases. For each of these cases we show that a specific anti-windup compensation structure (which is a generalization of the approach in the Proceedings of the Fourth ECC, Brussels, Belgium, July 1997) is capable of solving the anti-windup problem whenever this solvable. The effectiveness of the proposed scheme is shown on a simple example taken from the literature, in which the plant is a marginally stable linear system
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ItemStability of wireless and wireline networked control systems(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2007-09-01)This paper provides a general framework for analyzing the stability of general nonlinear networked control systems (NCS) with disturbances in the setting of cal Lp stability. Our presentation provides sharper results for both Lp gain and maximum allowable transfer interval (MATI) than previously obtainable and details the property of uniformly persistently exciting scheduling protocols. This class of protocols was shown to lead to cal Lp stability for high enough transmission rates and were a natural property to demand, especially in the design of wireless scheduling protocols. The property is used directly in a novel proof technique based on the notions of vector comparison and (quasi)-monotone systems. We explore these results through analytical comparisons to those in the literature, as well as through simulations and numerical comparisons that verify that the uniform persistence of excitation property of protocols is, in some sense, the "finest"property that can be extracted from wireless scheduling protocols.
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ItemQuadratic stabilization of linear networked control systems via simultaneous protocol and controller design(PERGAMON-ELSEVIER SCIENCE LTD, 2007-07-01)We derive conditions for quadratic stabilizability of linear networked control systems by dynamic output feedback and communication protocols. These conditions are used to develop a simultaneous design of controllers and protocols in terms of matrix inequalities. The obtained protocols do not require knowledge of controller and plant states but only of the discrepancies between current and the most recently transmitted values of nodes' signals, and are implementable on controller area networks. We demonstrate on a batch reactor example that our design guarantees quadratic stability with a significantly smaller network throughput than previously available designs.