This paper proposes a novel optimal digital redesign technique using fractional‐order hold (f.o.h.) for finding a dynamic digital control law from the available analog counterpart and for simultaneously minimizing a quadratic performance index. A method for converting the dynamic digital control law into a static one, through a tuning parameter, is also presented. The proposed technique can be applied to a system cascaded with a more general class of reference inputs than simple step inputs, and the developed digital controller can be implemented via low cost microcomputers. The superiority of using the fractional‐order hold over the zero‐order hold and the first‐order hold is exploited. © 1997 John Wiley & Sons, Ltd.

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A sufficient condition for delay-independent asymptotic stability of large-scale time-delay systems is derived. An evolutionary programming approach is newly developed to decompose the system matrix such that our result can be further improved. For testing the system stability, we do not attempt to solve the Lyapunov or Riccati equation, but need only to check the eigenvalues of a Hamiltonian matrix to guarantee the solvability of an algebraic Riccati equation. The present method is simple and less conservative than those proposed in the literature.

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