Electrical and Electronic Engineering - Research Publications
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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.
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ItemStability properties of reset systems(PERGAMON-ELSEVIER SCIENCE LTD, 2008-08-01)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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ItemPractical encoders for controlling nonlinear systems under communication constraints(ELSEVIER, 2008-08-01)We introduce a new class of dynamic encoders for continuous-time nonlinear control systems which update their parameters only at discrete times. We prove that the information reconstructed from the encoded feedback can be used to deliver a piece-wise constant control law which yields semi-global practical stability.
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ItemDecentralized control design of interconnected chains of integrators: A case study(PERGAMON-ELSEVIER SCIENCE LTD, 2008-08-01)We develop a constructive decentralized control design procedure for a class of systems that may be loosely described as chained integrators which are dynamically coupled. The design method is inspired by nested saturation control ideas and formulated by applying the singular perturbation theory. We demonstrate that the proposed design provides a Lyapunov function for an associated closed loop system from which semi-global stability may be deduced. Using the proposed idea, we design a semi-globally stabilizing control law for a four degree of freedom spherical inverted pendulum.
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ItemInput-output stability of networked control systems with stochastic protocols and channels(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008-06-01)This paper introduces a new definition of stochastic protocols for networked control systems (NCS) and the stochastic analog of the notion of uniform persistency of excitation of protocols first presented in the Proceedings of the 44th IEEE Conference on Decision and Control. Our framework applies directly to common wireless and wireline NCS, including those built on carrier-sense multiple access (CSMA) style protocols, with Ethernet and 802.11a/b/g as prime examples of this class. We present conditions for a general class of nonlinear NCS with exogenous disturbances using stochastic protocols in the presence of packet dropouts, random packet transmission times and collisions that are sufficient for Lp stability from exogenous disturbance to NCS state with a linear finite expected gain. Within the same framework, we extend the results of Nešić and Teel (see IEEE Trans. Autom. Control, vol. 49, no. 10, pp. 1650-1667, Oct. 2004) to provide an analysis of deterministic protocols, including try-once-discard (TOD), in the presence of random packet dropouts and intertransmission times and provide a stochastic analog of the Lyapunov-theoretic stability properties for network protocols introduced therein.
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ItemPulse amplification and gain recovery in semiconductor optical amplifiers: A systematic analytical approach(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008-05-01)Short-pulse propagation in semiconductor optical amplifiers (SOAs) has been widely studied for applications in optical signal processing and optical communications areas. Even though it is possible to integrate differential equations numerically, such implementations may not provide adequate insight into the device operation. We propose a systematic way to construct analytical solutions for the gain-recovery dynamics of SOAs and show excellent agreement with numerically integrated results. Our approach makes use of the multiple-scale technique. The main contribution of this work is to put earlier heuristic approaches into a firm theoretical base so that approximate analytical solutions for carrier-recovery dynamics can be systematically constructed for different variants of SOA models. We derive analytical solutions for the signal gain and pulse-energy gain at an arbitrary point with the SOA waveguide. Surpassing previous work in this area, we also show that it is possible to obtain analytical solutions when waveguide attenuation is not negligible.
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ItemOn the choice of dither in extremum seeking systems: A case study(PERGAMON-ELSEVIER SCIENCE LTD, 2008-05-01)We discuss how the choice of dither (excitation signal) affects the performance of extremum seeking using a benchmark situation: a static scalar map; and a simple scalar extremum seeking scheme. Our comparisons are based on the performance of the system with different dithers in terms of three performance indicators: the speed of convergence, domain of attraction and accuracy (i.e. the ultimate bound on trajectories). Our analysis explicitly shows how the dither shape affects each of these performance indicators. Our study suggests that the practitioners using extremum seeking control should consider the dither shape as an important design parameter. Computer simulations support our theoretical findings.
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ItemExtremum seeking control of cascaded Raman optical amplifiers(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008-05-01)This paper considers the control of a particular type of optical amplifier that finds application in long-haul wavelength division multiplexed optical communications systems. The objective of this consideration is to demonstrate an application of extremum seeking to the regulation of amplifier output signal power across a range of signal wavelengths, where limited control authority is available. Although such amplifiers are nonlinear and distributed parameter devices, an extremum seeking design is demonstrated to be a promising approach for achieving the stated amplifier control objectives.
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ItemOn l2 stabilization of linear systems with quantized control(Institute of Electrical and Electronics Engineers, 2008-02-01)This paper extends results from [D. Liberzon and D. Nesic, ldquoInput-to-state stabilization of linear systems with quantized feedback,rdquo IEEE Trans. Autom. Control, vol. 52, no. 5, pp. 767--781, May 2007], where input-to-state stabilization (ISS) of linear systems with quantized feedback was considered. In this paper, we show that, by using the same scheme and under the same conditions as in D. Liberzon and D. Nesic, ldquoInput-to-state stabilization of linear systems with quantized feedback,rdquo IEEE Trans. Autom. Control, vol. 52, no. 5, pp. 767-781, May 2007, it is also possible to achieve (nonlinear gain) l 2 stabilization for linear systems. We also prove a new lemma on K infin functions that is interesting in its own right.
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ItemNon-local stabilization of a spherical inverted pendulum(TAYLOR & FRANCIS LTD, 2008)We design a non-linear stabilizing control law for a four degree of freedom spherical inverted pendulum. The pendulum is a slim cylindrical beam attached to a horizontal plane via a universal joint; the joint is free to move in the plane under the influence of a planar force. The upright position is an unstable equilibrium of the uncontrolled system because of gravity. The objective is to design a controller so that it stabilizes the upright position starting from any position in the upper hemisphere with arbitrary velocity. We achieve this by first transforming the original system to an appropriate upper triangular form and then designing a controller which incorporates a high gain design with the method of non-linear forwarding. The control law is evaluated through computer simulations.