Electrical and Electronic Engineering - Research Publications

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    Two algorithms arising in analysis of polynomial models
    Nesic, D (IEEE, 1998)
    Algorithms for testing observability and forward accessibility of discrete-time polynomial systems are presented. The algorithms are based on symbolic computation packages - the Grobner basis method and QEPCAD. The observability test checks observability of general polynomial systems in finite time. Forward accessibility test is applicable to a large class of polynomial systems and also stops in finite time.
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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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    Observability for simple Wiener and simple Wiener-Hammerstein systems
    Nesic, D (IEEE, 1998-01-01)
    Necessary and sufficient conditions for observability are given for the class of simple Wiener-Hammerstein systems. The obtained observability test resembles the well known result for the series connection of two linear systems but it is subtly different. Observability tests that we present are very easy to use.
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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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    A simple controllability test for generalized Hammerstein models
    Nesic, D (IEEE, 1997-01-01)
    Simple necessary and sufficient conditions for deadbeat and complete controllability for a class of discrete-time generalized Hammerstein systems are derived. Due to the mild nonlinear structure of the considered systems, only linear algebra is used in the controllability test. A similar result is then proved for continuous-time generalized Hammerstein systems.
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    Stabilizing dead-beat controllers for two classes of Wiener-Hammerstein systems
    Nesic, D ; Bastin, G ; Lafay, JF (IFAC - International Federation of Automatic Control, 1998-01-01)
    Two classes of block oriented models of Wiener-Hammerstein type are considered. We prove that a generic condition is sufficient for a null controllable system of this form to have a stabilizing minimum-time dead-beat controller. In case the condition is violated, we show how to design a non-minimum time stabilizing (dynamic) dead-beat controller. The result can be used to obtain stabilizability conditions for these systems, which are the same as the linear conditions: all uncontrollable modes should be stable.
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    A note on stabilizing and time-optimal controllers for discrete-time linear systems with positive controls
    De Leenheer, P ; Nesic, D ; Huijberts, HJC ; Nijmeijer, H ; VanDerSchaft, AJ ; Scherpen, JMA (IFAC, 1998-01-01)
    Design of stabilizing and time-optimal controllers for discrete-time linear systems with positive controls is revisited. Necessary and sufficient conditions for stabilizability of this class of systems are given. A class of stabilizing controllers is designed. We show that a stabilizing time-optimal controller exists if the system is dead-beat controllable. We show by an example that there may also exist time-optimal controllers which are not stabilizing.