Electrical and Electronic Engineering - Research Publications
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ItemExplicit Lyapunov functions for stability and performance characterizations of FOREs connected to an integrator(IEEE, 2006)In this paper we provide explicit Lyapunov functions that prove that a First Order Reset Element (FORE) in negative feedback interconnection with an integrator is exponentially stable for any, positive or negative, value of the pole of the FORE. The Lyapunov functions also allow to establish finite gain L2 stability from a disturbance input acting at the input of the plant to the plant output. L2 stability is established by giving a bound on the corresponding L2 gains. The framework used for the characterization of the system dynamics and for the stability and performance analysis corresponds to the ideas first proposed in (Nesic et al. IFAC 2005) and (Zaccarian et al. ACC 2005).
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ItemOn cascaded raman amplifier control(IEEE, 2006-01-01)Extremum Seeking Control is applied to the control of cascaded Raman amplifiers for long-haul wavelength division multiplexed optical communications systems. Simulation demonstrates the effectiveness of this control strategy.
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ItemAn application of extremum seeking in cascaded optical amplifier control(IEEE, 2006)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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ItemA novel Smith predictor scheme applied to a fully actuated inverted pendulum(Elsevier Science, 2006)In this paper we show the effectiveness of a novel control scheme for deadtime systems recently proposed in (Zaccarian and Nesi_c, 2006 American Control Conference). In that paper, the prediction problem is formally stated and shown to be achievable for any type of dead-time system, as long as it is possible to determine a stabilizing control law. We propose here the employment of an LMI-based contro strategy for this stabilization task and show the advantages of the novel modified Smith predictor scheme on a MIMO example. In particular, satisfactory simulation results are given both for the linearized model and for the nonlinear model of an inverted pendulum subject to disturbances.
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ItemHigh order approximations by sampled-data feedback(MTNS 2006, 2006)Given a continuous time nonlinear closed loop system, we give explicit constructions for sampled–data feedback laws for which the trajectories of the sampled– data closed loop system converge to the continuous time trajectories with a prescribed rate of convergence as the sampling interval length tends to zero. In particular, we investigate necessary and sufficient conditions under which such sampled–data feedbacks exist. We give analytic solutions to the problem for local orders of convergence _ 4 and present a MAPLE code for general orders.
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ItemOn global extremum seeking in the presence of local extrema(IEEE, 2006-01-01)We analyze global extremum seeking in the presence of local extrema for static nonlinear maps controlled by a scalar extremum seeking scheme that was recently proposed in [1]. Sufficient conditions are given under which it is possible to tune the controller parameters to achieve convergence to an arbitrarily small neighborhood of the global extremum in the presence of local extrema from an arbitrarily large set of initial conditions. Several examples provide insights and highlight the potential difficulties that one would face when trying to generalize our results.
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ItemOn the choice of dither in extremum seeking systems: A case study(IEEE, 2006-01-01)We discuss how the dither (excitation signal) shape affects on 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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ItemSummability criteria for stability of sets for sampled-data nonlinear inclusions(IEEE, 2006)We present sufficient conditions for stability of parameterized difference inclusions that involve various summability criteria on functions of the trajectories of the system, to conclude global asymptotic stability and global exponential stability. Our theorems parallel similar results for continuous-time differential inclusions and extend previously published summability criteria for difference equations. They are tailored to be used within a framework for stabilization of sampled-data differential inclusions via their approximate discrete-time models, reported in a separate paper of this conference. We believe that these tools may become a useful addition to the "toolbox" for controller design for sampleddata nonlinear systems via their approximate discrete-time models.
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ItemOn stability of sets for sampled-data nonlinear inclusions via their approximate discrete-time models(IEEE, 2006-01-01)We generalize previous results on stability of sampled-data systems based on the approximate discrete-time models: we consider stabilization of arbitrary closed sets (not necessarily compact), 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 previous papers. We present checkable conditions that one can use to conclude semi-global practical asymptotic (SPA) stability, or global exponential stability (GES), of the sampled-data system via appropriate properties of its approximate discrete-time model. Thus, we provide a framework for stabilization of arbitrary closed sets for sampled-data nonlinear differential inclusions via their approximate discrete-time models.
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ItemSimultaneous controller and protocol design for networked control systems with packet based communication(IEEE, 2006-01-01)We derive conditions for quadratic stabilizability of linear networked control systems (LNCSs) by dynamic output feedback and communication protocols. We use these conditions 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 control area networks. We show on a batch reactor example that our design guarantees quadratic stability (QS) with a significantly smaller network bandwidth than previously available designs.