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Automatic Control, IEEE Transactions on

Issue 9 • Date Sept. 1998

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Displaying Results 1 - 25 of 29
  • Comments on "Robust, fragile, or optimal?" [with reply]

    Publication Year: 1998 , Page(s): 1265 - 1268
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (82 KB)  

    The issue of fragile controllers produced by using popular robust and optimal control synthesis methods was raised by Keel-Bhattacharyya in the above mentioned paper (ibid. vol.42 (1997)). The commenter points out that the controller fragility problem described in the paper is: 1) well known in the literature; 2) due to the poor choice of examples; 3) can easily be fixed by changing the optimization criteria; and 4) can be fixed by changing the implementation. In reply, Keel-Bhattacharyya disagree with him on all counts and explain their argument. View full abstract»

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  • Author's reply

    Publication Year: 1998 , Page(s): 1268
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (13 KB)  

    First Page of the Article
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  • Comments on "Mixed L/sup /spl infin///H/sub /spl infin// suboptimal controllers for SISO continuous time systems"

    Publication Year: 1998
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (39 KB)  

    The authors state that they have no serious criticism of the original paper but make certain remarks. An example in the original illustrates a method to do tradeoffs between two design goals: H/sub /spl infin// and L/sup /spl infin//. To make a fair comparison, they authors say that the optimal H/sub /spl infin// norm should have been presented. The also point out misprints, and make remarks on the cancellation of the integrator pole and the tending to /spl infin/ of the settling time. View full abstract»

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  • Comments on "Zeros of discretized continuous systems expressed in the Euler operator-an asymptotic analysis" [with reply]

    Publication Year: 1998 , Page(s): 1308 - 1310
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (127 KB)  

    In the original paper by Tesfaye and Tomizuka (ibid., vol.40, p.743-7, 1995), an asymptotic analysis was used to address the zero structure of discretized continuous-time systems expressed in the Euler (or forward difference) operator. The method was developed for application to multivariable control systems. The authors state that the analysis is flawed, so that a theorem is true as stated only when the continuous time relative degree is equal to two. They indicate how the analysis may be rectified. Tesfaye and Tomizuka acknowledge the error and the correctness of the result in this paper. View full abstract»

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  • Author's reply

    Publication Year: 1998 , Page(s): 1310
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (38 KB)  

    First Page of the Article
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  • Comments and further results regarding "On variable structure output feedback controllers"

    Publication Year: 1998 , Page(s): 1338 - 1340
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (82 KB)  

    This paper points out some misleading statements of the above-mentioned paper (Kwan, 1996) and shows that the proposed controller can be easily derived, under less restrictive conditions, from a previously proposed output feedback variable structure control scheme. View full abstract»

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  • Author's reply

    Publication Year: 1998 , Page(s): 1340
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (19 KB)  

    First Page of the Article
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  • Persistent identification and adaptation: stabilization of slowly varying systems in H

    Publication Year: 1998 , Page(s): 1211 - 1229
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    In this paper, the problem of persistent identification and adaptive stabilization of time-varying systems is studied within the framework of deterministic worst case identification and slow H adaptation. The plants under consideration are unstable and time-varying and cannot be stabilized by a fixed robust controller. Starting from an initial well-designed operating point, the controller must persistently adapt to the time-varying plant to maintain uniform stability over all future time. A key property which guarantees uniform stability is that the identification-adaptation iteration satisfies a certain invariance principle. We demonstrate that the adaptive design using periodic external inputs, least squares identification, and slow H adaptation possesses such an invariance property, leading to a successful adaptive stabilization methodology. Generic natures of our findings are discussed View full abstract»

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  • A martingale Kronecker lemma and parameter estimation for linear systems

    Publication Year: 1998 , Page(s): 1263 - 1265
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (124 KB)  

    A continuous-time martingale Kronecker lemma is proved and used to discuss parameter estimation for linear systems. The rates of convergence are discussed View full abstract»

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  • A result on exponential tracking error convergence and persistent excitation

    Publication Year: 1998 , Page(s): 1334 - 1338
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB)  

    Conditions are investigated for exponential convergence of the tracking error in feedforward adaptive systems having insufficient excitation. Particular attention is paid to the adaptive gradient algorithm with periodic excitation in the overparameterized case. A main result is that for a bounded periodic regressor, the tracking error converges exponentially without regard to parameter convergence or to the degree of overparameterization. These results weaken the persistent excitation (PE) conditions and parameter convergence conditions generally considered necessary to ensure exponential tracking convergence in this class of systems View full abstract»

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  • A direct characterization of L2-gain controllers for LPV systems

    Publication Year: 1998 , Page(s): 1302 - 1307
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    In this paper, a class of linear parameter dependent output feedback controllers that satisfy quadratic stability and an induced L 2-norm bound for a given linear parameter-varying (LPV) plant is considered. By using a parameter-independent common Lyapunov function, the solvability conditions are expressed in terms of finite dimensional linear matrix inequalities (LMI) evaluated at the extreme points of the admissible parameter set. Conditions under which strictly proper controllers can be used are obtained. By restricting some of the controller matrices to be constant, the input and output matrices can be parameter-varying without destroying the problem's convexity. Cases where the controller matrices can be obtained without interpolation are also discussed, thereby simplifying the implementation of the controller. A numerical example is included which demonstrates the application of the results View full abstract»

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  • Parametrization of nonlinear stabilizing controllers: the observer-controller configuration

    Publication Year: 1998 , Page(s): 1268 - 1272
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (132 KB)  

    The paper uses the author's (1996) previous results to develop the parametrization of nonlinear stabilizing observer-controller compensators of a given nonlinear system. The configuration described permits a simple parametrization of stabilizing controllers using coprime factorisation techniques View full abstract»

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  • Pole placement capabilities of vibrational control

    Publication Year: 1998 , Page(s): 1256 - 1261
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB)  

    Vibrational control modifies the system dynamics by introducing fast zero-average parametric oscillations. However, this property is constrained by the trace invariance condition which limits the pole placement capabilities. This paper provides the necessary and sufficient conditions under which pole assignment by vibrational control in certain parts of the complex plane is possible View full abstract»

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  • Adaptive tracking strategy for a class of nonlinear systems

    Publication Year: 1998 , Page(s): 1272 - 1279
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    This paper presents an adaptive feedback tracking strategy for a class of uncertain single-input/single-output systems in strict parametric feedback form with nonlinear time-varying parameterization. The tracking scheme is based on a backstepping design. A local stability result is obtained via Lyapunov arguments View full abstract»

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  • Model-free control of nonlinear stochastic systems with discrete-time measurements

    Publication Year: 1998 , Page(s): 1198 - 1210
    Cited by:  Papers (88)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    Consider the problem of developing a controller for general (nonlinear and stochastic) systems where the equations governing the system are unknown. Using discrete-time measurement, this paper presents an approach for estimating a controller without building or assuming a model for the system. Such an approach has potential advantages in accommodating complex systems with possibly time-varying dynamics. The controller is constructed through use of a function approximator, such as a neural network or polynomial. This paper considers the use of the simultaneous perturbation stochastic approximation algorithm which requires only system measurements. A convergence result for stochastic approximation algorithms with time-varying objective functions and feedback is established. It is shown that this algorithm can greatly enhance the efficiency over more standard stochastic approximation algorithms based on finite-difference gradient approximations View full abstract»

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  • Dampening controllers via a Riccati equation approach

    Publication Year: 1998 , Page(s): 1280 - 1284
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    An algorithm is presented which computes a state feedback for a standard linear system which not only stabilizes, but also dampens the closed-loop system dynamics. In other words, a feedback gain matrix is computed such that the eigenvalues of the closed-loop state matrix are within the region of the left half-plane where the magnitude of the real part of each eigenvalue is greater than that of the imaginary part, This may be accomplished by solving a damped algebraic Riccati equation and a degenerate Riccati equation. The solution to these equations are computed using numerically robust algorithms, Damped Riccati equations are unusual in that they may be formulated as an invariant subspace problem of a related periodic Hamiltonian system. This periodic Hamiltonian system induces two damped Riccati equations: one with a symmetric solution and another with a skew symmetric solution. These two solutions result in two different state feedbacks, both of which dampen the system dynamics, but produce different closed-loop eigenvalues, thus giving the controller designer greater freedom in choosing a desired feedback View full abstract»

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  • On the language generated under fully decentralized supervision

    Publication Year: 1998 , Page(s): 1253 - 1256
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB)  

    This paper studies the language generated under fully decentralized supervision proposed by Kozak and Wonham (1995). The author assumes that desirable behavior is specified as a closed language. A closed-form expression for the language generated under fully decentralized supervision is presented. It is shown that the generated language is larger than the supremal closed, controllable, and strongly decomposable sublanguage. Moreover, a necessary and sufficient condition is derived for the generated language to be the supremal closed and controllable sublanguage View full abstract»

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  • System zeros analysis via the Moore-Penrose pseudoinverse and SVD of the first nonzero Markov parameter

    Publication Year: 1998 , Page(s): 1285 - 1291
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    A new characterization of system zeros of an arbitrary linear system described by a state-space model S(A, B, C, D) is presented. The transmission zeros are characterized as invariant zeros of an appropriate strictly proper system with a smaller number of inputs and outputs than the original system. The approach is based on singular value decomposition (SVD) of the first nonzero Markov parameter. This result together with characterization of invariant and decoupling zeros, based on the Moore-Penrose inverse of the first nonzero Markov parameter and the Kalman canonical decomposition theorem, provided in the first part of the paper yield a complete characterization of system zeros of an arbitrary multi-input/multi-output system View full abstract»

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  • Set membership approach for reducing value sets in the frequency domain

    Publication Year: 1998 , Page(s): 1346 - 1350
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    Previously, several nonparametric robust identification algorithms have been proposed that generate a collection of frequency-dependent value sets where the true model of a linear time-invariant system is assumed to lie. If the system is also assumed to have restricted complexity, then the identified value sets may be conservative. The purpose of this paper is to investigate this problem of conservativeness from a set membership viewpoint and propose an algorithm for computing the largest value sets contained in the original ones that can be generated by a model of fixed structure but unknown parameters View full abstract»

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  • A quadratic programming approach for solving the l1 multiblock problem

    Publication Year: 1998 , Page(s): 1242 - 1252
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    The authors present a new method to compute solutions to the general multiblock l1 control problem. The method is based on solving a standard H2 problem and a finite-dimensional semidefinite quadratic programming problem of appropriate dimension. The new method has most of the properties that separately characterize many existing approaches. In particular, as the dimension of the quadratic programming problem increases, this method provides converging upper and lower bounds on the optimal l1 norm and, for well posed multiblock problems, ensures the convergence in norm of the suboptimal solutions to an optimal l1 solution. The new method does not require the computation of the interpolation conditions, and it allows the direct computation of the suboptimal controller View full abstract»

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  • H2 guaranteed cost control for singularly perturbed uncertain systems

    Publication Year: 1998 , Page(s): 1323 - 1329
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    The H2 guaranteed cost control problem for a singularly perturbed norm-bounded uncertain system is addressed using the quadratic stabilizability framework. After defining the corresponding slow and fast uncertain subsystems, the set of quadratic stabilizing composite controls is characterized. Two Riccati equations have to be solved, one for the slow subsystem and the other for the fast subsystem. Choosing appropriately the weighting matrices, it is shown how to pick up in the set of quadratic stabilizing composite controls, a control minimizing an upper bound on the H2 norm of a certain transfer matrix. The case of the guaranteed cost control problem for the reduced system is also investigated View full abstract»

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  • Robust stability of sampled-data systems under possibly unstable additive/multiplicative perturbations

    Publication Year: 1998 , Page(s): 1340 - 1346
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    Applies the FR-operator technique to the robust stability problem of sampled-data systems against additive/multiplicative perturbations, where a reasonable class of perturbations consists of unstable as well as stable ones. Assuming that the number of unstable modes of the plant does not change, we show that a small-gain condition in terms of the FR-operator representation (which is actually equivalent to a small-gain condition in terms of the L2-induced norm) is still necessary and sufficient for the sampled-data system to be robustly stable against h-periodic perturbations, in spite of their possible instability. The result is derived by a Nyquist-type of arguments. Next, a necessary and sufficient condition for robust stability against linear time-invariant (LTI) perturbations is also given. Furthermore, we show that if the plant is either single-input or single-output, the condition can be reduced to a readily testable form. Finally, we clarify when the small-gain condition becomes a particularly poor measure for robust stability View full abstract»

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  • On the bias of the modified output error algorithm

    Publication Year: 1998 , Page(s): 1261 - 1262
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (92 KB)  

    In a recent work by Betser and Zeheb (1995), a modified adaptive output error algorithm for identification was proposed. In this paper, we prove that the solution is biased for most practical types of disturbance noise, including the white noise case. Bias can be avoided in certain cases, under the verification of a relation between the spectrum of the noise and the noise-free solution, specified in the form of a theorem View full abstract»

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  • A homotopy approach for nonlinear control synthesis

    Publication Year: 1998 , Page(s): 1311 - 1318
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    In this paper, the authors propose a control method for nonlinear systems which relies on the homotopy method for solving nonlinear equations and tangent linearized control systems. They present a mathematically rigorous treatment of the theoretical foundations, including a constructive proof of the exponential error decay for the controlled system which contains an explicit control design instruction. For illustration, this design instruction is applied to an example system. The behavior of the controlled system is examined by numerical simulations. To demonstrate the advantages and drawbacks of the proposed method they include a short comparison with two usual nonlinear control techniques by means of the considered example system View full abstract»

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  • Timed-event graphs with multipliers and homogeneous min-plus systems

    Publication Year: 1998 , Page(s): 1296 - 1302
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    The authors study fluid analogues of a subclass of Petri nets, called fluid timed event graphs with multipliers, which are a timed extension of weighted T systems studied in the Petri net literature. These event graphs can be studied naturally, with a new algebra, analogous to the min-plus algebra, but defined on piecewise linear concave increasing functions, endowed with the pointwise minimum as addition and the composition of functions as multiplication. A subclass of dynamical systems in this algebra, which have a property of homogeneity, can be reduced to standard min-plus linear systems after a change of counting units. The authors give a necessary and sufficient condition under which a fluid timed-event graph with multipliers can be reduced to a fluid timed event graph without multipliers. In the fluid case, this class corresponds to the so-called expansible timed-event graphs with multipliers of Munier (1993), or to conservative weighted T-systems. The change of variable is called here a potential. Its restriction to the transition nodes of the event graph is a T-semiflow View full abstract»

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Aims & Scope

In the IEEE Transactions on Automatic Control, the IEEE Control Systems Society publishes high-quality papers on the theory, design, and applications of control engineering.  Two types of contributions are regularly considered

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Meet Our Editors

Editor-in-Chief
P. J. Antsaklis
Dept. Electrical Engineering
University of Notre Dame