D.J. Clements

Papers: Algebraic characterization of fixed modes in decentralized control

Algebraic characterizations are presented for the existence of fixed modes of a linear closed-loop system with decentralized feedback control. The class of controllers for which fixed modes are present is extended beyond that currently known.

Spectral factorization via Hermitian pencils

Abstract The spectral factorization problem is solved for state-space systems via results on the canonical forms and inertia of Hermitian matrix pencils. These algebraic results then give a deflation method for spectral factorization.

Optimal control computation for nonlinear time-lag systems

In this paper, a computational scheme using the technique of control parameterization is developed for solving a class of optimal control problems involving nonlinear hereditary systems with linear control constraints. Several examples have been solved to test the efficiency of the technique.

Controller design for hot strip finishing mills

The results to date of a collaborative research project with BHP Steel in Port Kembla, Australia, are described. The project is concerned with control of strip tension and looper angle in BHPs hot strip steel rolling mill (the finishing mill). The new controllers have been successfully implemented on the process and now handle all the production at the mill. The paper describes a model of the process, similar to that reported in the work of others. The development of a full nonlinear controller is traced, based on a recursive nonlinear method (cf., backstepping). Insights are drawn into possible system structures, particularly in the output feedback case when tension measurements may not be available. Alternative controller schemes are examined, including a speculative design which contains filters, similar to those obtained from output feedback designs of linear systems, together with nonlinear operators which invite comparisons with variable structure designs. Simulation results, which provided the justification for the final implementation, together with results from actual production records are presented.

The robustness properties of the linear quadratic regulators for singular systems

The LQR (linear quadratic regulator) robustness properties of singular systems are investigated. It is shown that the optimal regulators for singular systems with an appropriate selection of the feedback gain have the same robustness properties as those in regular systems, namely, at least 60 degrees guaranteed phase margin, infinite gain margin, and 50% gain reduction margin. >

Optimal control computation for linear time-lag systems with linear terminal constraints

A computational scheme using the technique of control parameterization is developed for solving a class of optimal control problems involving linear hereditary systems with bounded control region and linear terminal constraints. Several examples have been solved to illustrate the efficiency of the technique.

Polynomial Factorization via the Riccati Equation

The paper tackles the problem of factoring a real polynomial

Spectral factorization with imaginary-axis zeros

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Rational spectral factorization using state-space methods

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Adaptive mould level control for continuous steel slab casting

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