Electrical and Electronic Engineering - Research Publications
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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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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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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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ItemOn non-local stability properties of extrernum seeking control(PERGAMON-ELSEVIER SCIENCE LTD, 2006-06-01)In this paper, we consider several extremum seeking schemes and show under appropriate conditions that these schemes achieve extremum seeking from an arbitrarily large domain of initial conditions if the parameters in the controller are appropriately adjusted. This non-local stability result is proved by showing semi-global practical stability of the closed-loop system with respect to the design parameters. We show that reducing the size of the parameters typically slows down the convergence rate of the extremum seeking controllers and enlarges the domain of the attraction. Our results provide guidelines on how to tune the controller parameters in order to achieve extremum seeking. Simulation examples illustrate our results.
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ItemExtremum Seeking Control with Sporadic Packet Transmission for Networked Control Systems(IEEE, 2020-06)Extremum Seeking Control (ESC) is a data-driven optimization technique that can steer a dynamic plant towards an extremum of an unknown but measurable, input to steady-state map. In the context of Networked Control Systems (NCS) a new implementation method for ESC inspired by the well known Luus-Jaakola algorithm is proposed. The main motivation is to minimize the communication burden associated with the search phase of ESC. In the proposed method the controller only requires a notification of a change registered at the sensor, rather than the full information available at the sensor. This event based approach leads to sporadic packet transmission. In addition the proposed method is able to directly account for constraints whilst seeking for the desired extremum. The constraints may be of the inequality or equality type. The algorithm's behavior is illustrated on a networked water pump control system.
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ItemLearning control in robot-assisted rehabilitation of motor skills–a review(Informa UK Limited, 2016-01-02)