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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ItemOn controller & capacity allocation co-design for networked control systems(ELSEVIER, 2009-09-01)This paper presents a framework for examining joint optimal channel-capacity allocation and controller design for networked control systems using store-and-forward networks in a discrete-time linear time-invariant setting. The resultant framework provides a synthesis procedure for designing distributed linear control laws for capacity-constrained networks taking the allocation of the capacity within the network into account.
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ItemOn Extremum Seeking in Bioprocesses with Multivalued Cost Functions(WILEY, 2009)Finding optimal operating modes for bioprocesses has been, for a long time, a relevant issue in bioengineering. The problem is of special interest when it implies the simultaneous optimization of competing objectives. In this paper, we address the problem of finding optimal steady states that achieve the best tradeoff between yield and productivity by using nonmodel-based extremum-seeking control with semiglobal practical stability and convergence properties. A special attention is paid to processes with multiple steady states and multivalued cost functions.
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ItemExtremum Seeking Control: Convergence Analysis(ELSEVIER, 2009-05-01)This paper summarizes our recent work on dynamical properties for a class of extremum seeking (ES) controllers that have attracted a great deal of research attention in the past decade. Their local stability properties were already investigated, see [2]. We first show that semi-global practical convergence is possible if the controller parameters are carefully tuned and the objective function has a unique (global) extremum. An interesting tradeoff between the convergence rate and the size of the domain of attraction of the scheme is uncovered: the larger the domain of attraction, the slower the convergence of the algorithm. The amplitude, frequency and shape of the dither signal are important design parameters in the extremum seeking controller. In particular, we show that changing the amplitude of the dither adaptively can be used to deal with global extremum seeking in presence of local extrema. Moreover, we show that the convergence of the algorithm is proportional to the power of the dither signal. Consequently, the square-wave dither yields the fastest convergence among all dithers of the same frequency and amplitude. We consider extremum seeking of a class of bioprocesses to demonstrate our results and motivate some open research questions for multi-valued objective functions.
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ItemA Unified Framework for Design and Analysis of Networked and Quantized Control Systems(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2009-04-01)We generalize and unify a range of recent results in quantized control systems (QCS) and networked control systems (NCS) literature and provide a unified framework for controller design for control systems with quantization and time scheduling via an emulation-like approach. A crucial step in our proofs is finding an appropriate Lyapunov function for the quantization/time-scheduling protocol which verifies its uniform global exponential stability (UGES). We construct Lyapunov functions for several representative protocols that are commonly found in the literature, as well as some new protocols not considered previously. Our approach is flexible and amenable to further extensions which are briefly discussed.
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ItemRobustness of quantized control systems with mismatch between coder/decoder initializations(PERGAMON-ELSEVIER SCIENCE LTD, 2009-03-01)This paper analyzes the stability of linear systems with quantized feedback in the presence of mismatch between the initial conditions at the coder and decoder. Under the assumption of the perfect channel, we show that using the scheme proposed in [Liberzon, D., & Nešić, D. (2007). Input-to-state stabilization of linear systems with quantized state measurements. Institute of Electrical and Electronic Engineers Transaction on Automatic Control, 52, 767-781] it is possible to achieve stability with exponential convergence of linear systems with quantized feedback when the coder and decoder are initialized at different initial conditions.
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ItemExplicit Computation of the Sampling Period in Emulation of Controllers for Nonlinear Sampled-Data Systems(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2009-03-01)The purpose of this note is to apply recent results on stabilization of networked control systems to obtain an explicit formula for the maximum allowable sampling period (MASP) that guarantees stability of a nonlinear sampled-data system with an emulated controller. Such formulas are of great value to control practitioners.
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ItemON STABILITY OF SETS FOR SAMPLED-DATA NONLINEAR INCLUSIONS VIA THEIR APPROXIMATE DISCRETE-TIME MODELS AND SUMMABILITY CRITERIA(SIAM PUBLICATIONS, 2009-01-01)This paper consists of two main parts. In the first part, we provide a framework for stabilization of arbitrary (not necessarily compact) closed sets for sampled-data nonlinear differential inclusions via their approximate discrete-time models. We generalize [D. Nešiĉ, A. R. Teel, and P. V. Kokotović, Systems Control Lett., 38 (1999), pp. 259-270, Theorem 1] in several different directions: we consider stabilization of arbitrary closed sets, plants described as sampled-data differential inclusions, and arbitrary dynamic controllers in the form of difference inclusions. Our result does not require the knowledge of a Lyapunov function for the approximate model, which is a standing assumption in [D. Nešić and A. R. Teel, IEEE Trans. Automat. Control, 49 (2004), pp. 1103-1122] and [D. Nešić, A. R. Teel, and P. V. Kokotović, Systems Control Lett., 38 (1999), pp. 259-270, Theorem 2]. We present checkable conditions that one can use to conclude semiglobal asymptotic stability, or global exponential stability (GES), of the sampled-data system via appropriate properties of its approximate discrete-time model. In the second part, we present sufficient conditions for stability of parameterized difference inclusions that involve various summability criteria on trajectories of the system to conclude global asymptotic stability (GAS) or GES, and they represent discrete-time counterparts of results given in [A. R. Teel, E. Panteley, and A. Loria, Math. Control Signals Systems, 15 (2002), pp. 177-201]. These summability criteria are not Lyapunov based, and they are tailored to be used within our above-mentioned framework for stabilization of sampled-data differential inclusions via their approximate discrete-time models. We believe that these tools will be a useful addition to the toolbox for controller design for sampled-data nonlinear systems via their approximate discrete-time models.
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ItemOn global extremum seeking in the presence of local extrema(PERGAMON-ELSEVIER SCIENCE LTD, 2009-01-01)We propose a global extremum seeking scheme which can seek the global optimal value in the presence of local extrema. It is shown that the proposed global extremum seeking scheme can converge to an arbitrarily small neighborhood of the global extremum from an arbitrarily large set of initial conditions if sufficient conditions are satisfied. A simple example illustrates the effectiveness of the proposed scheme.
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ItemObserver design for wired linear networked control systems using matrix inequalities(PERGAMON-ELSEVIER SCIENCE LTD, 2008-11-01)We design an observer-protocol pair to asymptotically reconstruct the states of a linear time-invariant (LTI) plant under communication constraints induced by the network. We parameterize a class of observers and protocols, and for a given network transmission interval, we derive sufficient conditions in terms of matrix inequalities for the existence of an observer-protocol pair in the considered class that asymptotically reconstructs the plant states.