Electrical and Electronic Engineering - Research Publications
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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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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.
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ItemLyapunov functions for time-varying systems satisfying generalized conditions of Matrosov theorem(SPRINGER LONDON LTD, 2007-05-01)The classical Matrosov theorem concludes uniform asymptotic stability of time-varying systems via a weak Lyapunov function (positive definite, decrescent, with negative semi-definite derivative along solutions) and another auxiliary function with derivative that is strictly nonzero where the derivative of the Lyapunov function is zero (Mastrosov in J Appl Math Mech 26:1337-1353, 1962). Recently, several generalizations of the classical Matrosov theorem have been reported in Loria et al. (IEEE Trans Autom Control 50:183-198, 2005). None of these results provides a construction of a strong Lyapunov function (positive definite, decrescent, with negative definite derivative along solutions) which is a very useful analysis and controller design tool for nonlinear systems. Inspired by generalized Matrosov conditions in Loria et al. (IEEE Trans Autom Control 50:183-198, 2005), we provide a construction of a strong Lyapunov function via an appropriate weak Lyapunov function and a set of Lyapunov-like functions whose derivatives along solutions of the system satisfy inequalities that have a particular triangular structure. Our results will be very useful in a range of situations where strong Lyapunov functions are needed, such as robustness analysis and Lyapunov function-based controller redesign. We illustrate our results by constructing a strong Lyapunov function for a simple Euler-Lagrange system controlled by an adaptive controller and use this result to determine an ISS controller.
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ItemInput-to-state stabilization of linear systems with quantized state measurements(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2007-05-01)We consider the problem of achieving input-to-state stability (ISS) with respect to external disturbances for control systems with linear dynamics and quantized state measurements. Quantizers considered in this paper take finitely many values and have an adjustable "zoom"parameter. Building on an approach applied previously to systems with no disturbances, we develop a control methodology that counteracts an unknown disturbance by switching repeatedly between "zooming out" and "zooming in." Two specific control strategies that yield ISS are presented. The first one is implemented in continuous time and analyzed with the help of a Lyapunov function, similarly to earlier work. The second strategy incorporates time sampling, and its analysis is novel in that it is completely trajectory-based and utilizes a cascade structure of the closed-loop hybrid system. We discover that in the presence of disturbances, time-sampling implementation requires an additional modification which has not been considered in previous work.
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ItemA Lyapunov proof of an improved maximum allowable transfer interval for networked control systems(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2007-05-01)Simple Lyapunov proofs are given for an improved (relative to previous results that have appeared in the literature) bound on the maximum allowable transfer interval to guarantee global asymptotic or exponential stability in networked control systems and also for semiglobal practical asymptotic stability with respect to the length of the maximum allowable transfer interval.
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ItemPath-following for nonlinear systems with unstable zero dynamics(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2007-03-01)In the path-following problem formulated in this note, it is required that the error between the system output and the desired geometric path eventually be less than any prespecifled constant. If in a nonlinear multiple-input-multiple- output (MIMO) system the output derivatives do not enter into its zero dynamics, a condition relating path geometry and stabilizability of the zero dynamics is given under which a solution to this problem exists. The solution is obtained by combining input-to-state stability and hybrid system methodologies.
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ItemRaQ: A robust active queue management scheme based on rate and queue length(ELSEVIER, 2007-06-08)
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ItemInstability effects of two-way traffic in a TCP/AQM system(ELSEVIER, 2007-07-31)