Electrical and Electronic Engineering - Research Publications
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ItemNonlinear sampled-data observer design via approximate discrete-time models and emulation(International Federation of Automatic Control, 2005)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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ItemConditions for uniform boundedness of parameterized discrete-time cascades(ACPA Asian Control Professors' Association, 2004)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 ap propriate 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(IEEE, 2004-01-01)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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Item/spl Lscr//sub 2/ anti-windup for linear dead-time systems(IEEE, 2004)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 the anti-windup construction problem in the global, local, robust and nominal cases. For each of these cases we show that a specific anti-windup compensation structure is capable of solving the anti-windup problem whenever this is 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 time-varying discrete-time cascades(IFAC, 2002)Stability results for analysis of time-varying discrete-time cascaded systems are presented. Most of these results parallel their continuous-time counterparts although there are some important differences in the proof techniques that are used. More importantly, some fundamental differences between stability properties of discrete-time and continuous-time cascades are pointed out and illustrated via examples.
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ItemInput to state stability of pulse width modulated control systems(University of Notre Dame, 2002)New results on set stability and input-to-state stability in pulse-width modulated (PWM) control systems with disturbances are presented. The results are based on a recent generalization of two time scale stability theory to di®erential equations with disturbances. In particular, averaging theory for systems with disturbances is used to establish the results. The nonsmooth nature of PWM systems is accommodated by working with upper semicontinuous set-valued maps, locally Lipschitz in°ations of these maps, and locally Lipschitz parameterizations of locally Lipschitz set-valued maps.
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ItemAveraging with respect to arbitrary closed sets: closeness of solutions for systems with disturbances(IEEE, 2000)We consider two different definitions of "average" for systems with disturbances: the "strong" and "weak" averages that were introduced in [7]. Our definitions are more general than those in [7] as we use the distance to an arbitrary closed set A instead of the Euclidean norm for states in the definitions of averages. This generalization allows us to deal with more general cases of averaging for systems with disturbances, such as partial averaging. Under appropriate conditions, the solutions of a time-varying system with disturbances are shown to converge uniformly on compact time intervals to the solutions of the system's average as the rate of change of time increases to infinity.
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ItemChanging supply rates for input-output to STA testable discrete-time systems(Elsevier Science, 2002)We present results on changing supply rates for input-output to state stable (IOSS) discrete-time nonlinear systems. Our results can be used to combine two Lyapunov functions, none of which can be used to verify that the system has a certain property, into a new Lyapunov function from which the property of interest can be concluded.We present several applications of our results to discrete-time systems such as a l_a Lasalle criteria for input to state stability (ISS) and input to state stability with positive semide_nite Lyapunov functions.
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ItemStabilization of sampled-data nonlinear systems via their approximate models:: an optimization based approach(IEEE, 2002)We present results on numerical regulator design for sampled-data nonlinear plants via their approximate discrete-time plant models. The regulator design is based on an approximate discrete-time plant model and is carried out either via an infinite horizon optimization problem or via a finite horizon with terminal cost optimization problem. We focus on the case when the sampling period T and the accuracy parameter h of the approximate discrete-time plant model are independent of each other and show that with this approach practical and/or semiglobal stability of the exact discrete-time model is achieved under appropriate conditions.
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ItemA concept of Department of Control Systems(IFAC, 2001-01-01)A concept of the Department of Control Systems is proposed. Motivation for doing this comes from the fact that the field of automatic control has reached its maturity as a scientific and engineering discipline, which is characterised by its specific, original and important goals, problems, methods, methodologies, techniques and technologies. Analysis, synthesis, design, realisation, implementation, maintenance and development of control devices, of controllers and of controlled plants demand highly responsible and fully competent engineers. It is evaluated that they should be educated at the undergraduate level in the Department of Control Systems to become complete automatic control engineers (for short: control engineers).