Electrical and Electronic Engineering - Research Publications

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    Point-wise extremum seeking control scheme under repeatable control environment
    Tan, Y ; Mareels, I ; Nešić, D ; Xu, JX (IEEE, 2007-01-01)
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    Extremum Seeking From 1922 To 2010
    Tan, Y ; Moase, WH ; Manzie, C ; Nesic, D ; Mareels, IMY ; Chen, J (IEEE, 2010-01-01)
    Extremum seeking is a form of adaptive control where the steady-state input-output characteristic is optimized, without requiring any explicit knowledge about this input-output characteristic other than that it exists and that it has an extremum. Because extremum seeking is model free, it has proven to be both robust and effective in many different application domains. Equally being model free, there are clear limitations to what can be achieved. Perhaps paradoxically, although being model free, extremum seeking is a gradient based optimization technique. Extremum seeking relies on an appropriate exploration of the process to be optimized to provide the user with an approximate gradient, and hence the means to locate an extremum. These observations are elucidated in the paper. Using averaging and time-scale separation ideas more generally, the main behavioral characteristics of the simplest (model free) extremum seeking algorithm are established.
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    On the use of switched linear controllers for stabilizability of implicit recursive equations
    Nesic, D (IEEE, 1998-01-01)
    Stabilizability of implicit recursive equations is investigated. These equations arise naturally in the context of output dead-beat control for systems described by NARMAX models. Due to non-uniqueness of the solutions of these equations a special kind of a constrained stabilizability problem is considered. We take a hybrid switching control approach in testing the existence of a locally stabilizing controller. A method for the design of a stabilizing switching controller is also presented.
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    Stability of high order polynomial dynamics and minimum phase discrete-time systems
    Nešić, D ; Mareels, IMY (IEEE, 1997-04-08)
    The definition of a minimum phase nonlinear system, as usually found in the literature, is not general enough to be used for some classes of systems. The nonlinearity may yield a variety of different behaviors that are not addressed and analyzed in the literature. We provide a constructive method to test several different minimum phase properties for classes of explicit and implicit discrete-time polynomial systems. The method is based on a symbolic computation package called QEPCAD. Our results can also be interpreted as a constructive approach to stability and stabilizability of explicit and implicit discrete-time polynomial systems.
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    An output dead beat controllability test for a class of odd polynomial systems
    Nešić, D ; Mareels, IMY (IEEE, 1997-04-08)
    An output dead beat controllability test that stops after finitely many rational operations is presented for a class of odd polynomial systems. The test is based on the Gröbner basis method but it needs to be facilitated in general with the QEPCAD symbolic computation package. Geometric properties due to which output dead beat controllability may be lost are identified and analysed. The computational requirements are smaller when compared with the known output dead beat controllability tests.
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    On some triangular structures and the state dead-beat problem for polynomial systems
    Nesic, D ; Mareels, IMY (I E E E, 1997-01-01)
    QEPCAD based controllability testing for polynomial discrete-time systems is computationally very expensive and it may lead to non-terminating algorithms. We identify the structure of a large class of polynomial discrete-time systems, which reduces the computational cost associated with the dead-beat controllability test and which may lead to finite time controllability tests. For this purpose we use QEPCAD and the Grobner basis method. The structure which we identify encompases several classes of systems for which dead-beat controllability tests exist.
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    Analysis of minimum phase properties for non-affine nonlinear systems
    Nesic, D ; Skafidas, E ; Mareels, IMY ; Evans, RJ (IEEE, 1997-01-01)
    A system can be termed non-minimum phase according to some definitions available in the literature and yet the same system may exhibit stable zero output constrained dynamics. We show that for non-affine nonlinear systems there may not exist a continuous control law which would keep the output identically equal to zero and for which the zero output constrained dynamics are stable, whereas a discontinuous controller which achieves this exists. We give conditions for existence and present a method for design of discontinuous switching controllers which yield stable zero dynamics. In this sense, the results of this paper enlarge the class of non-affine nonlinear systems that can be termed minimum-phase.
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    Necessary and sufficient conditions for output dead beat controllability for a class of polynomial systems
    Nesic, D ; Mareels, I ; Bastin, G ; Mahoney, R (I E E E, 1995-01-01)
    Output dead beat control for a class of non linear discrete time systems, which are described by a single input-output polynomial difference equation, is considered. Necessary and sufficient conditions for the existence of output dead beat control (or output controllability in finite time) are presented. A tractable output dead beat controllability test is obtained.
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    A note on the control of a spherical inverted pendulum
    Liu, G ; Mareels, I ; Nešić, D (IFAC, 2007-01-01)
    We carry out extensive numerical simulations of a spherical inverted pendulum with various controllers to verify our theoretical developments. The simulations are useful in quantitatively understanding the operation of the system with different controllers and checking that the theoretical results are consistent with the numerical results. Using the numerical simulations, we also discuss in some detail various important aspects of the performance of the closed loop systems in order to compare the controllers.
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    On automatic seeking of optimal steady-states in biochemical processes
    Bastin, G ; Nešić, D ; Tan, Y ; Mareels, I (IFAC, 2007-01-01)
    It is discussed how the automatic seeking of optimal steady states biochemical reactors can be achieved by using non-model based extremum-seeking control with semi-global practical stability and convergence properties. A special attention is paid to processes with multiple steady-states and multivalued cost functions.