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Delay Margin (delay + margin)
Selected AbstractsComputation of time delay margin for power system small-signal stabilityEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 7 2009Saffet AyasunArticle first published online: 19 JUN 200 Abstract With the extensive use of phasor measurement units (PMU) in the wide-area measurement/monitoring systems (WAMS), time delays have become unavoidable in power systems. This paper presents a direct and exact method to compute the delay margin of power systems with single and commensurate time delays. The delay margin is the maximum amount of time delay that the system can tolerate before it becomes unstable for a given operating point. First, without using any approximation or substitution, the transcendental characteristic equation is converted into a polynomial without the transcendentality such that its real roots coincide with the imaginary roots of the characteristic equation exactly. The resulting polynomial also enables us to easily determine the delay dependency of the system stability and the sensitivities of crossing roots with respect to time delay. Then, an expression in terms of system parameters and imaginary root of the characteristic equation is derived for computing the delay margin. The proposed method is applied to a single-machine-infinite bus (SMIB) power system with an exciter. Delay margins are computed for a wide range of system parameters including generator mechanical power, damping and transient reactance, exciter gain, and transmission line reactance. The results indicate that the delay margin decreases as the mechanical power, exciter gain and line reactance increase while it increases with increasing generator transient reactance Additionally, the relationship between the delay margin and generator damping is found be relatively complex. Finally, the theoretical delay margin results are validated using the time-domain simulations of Matlab. Copyright © 2008 John Wiley & Sons, Ltd. [source] New results for the analysis of linear systems with time-invariant delaysINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 12 2003Jianrong Zhang Abstract This paper presents a comparison system approach for the analysis of stability and ,, performance of linear time-invariant systems with unknown delays. The comparison system is developed by replacing the delay elements with certain parameter-dependent Padé approximations. It is shown using the special properties of the Padé approximation to e,s that the value sets of these approximations provide outer and inner coverings for that of each delay element and that the robust stability of the outer covering system is a sufficient condition for the stability of the original time delay system. The inner covering system, in turn, is used to provide an upper bound on the degree of conservatism of the delay margin established by the sufficient condition. This upper bound is dependent only upon the Padé approximation order and may be made arbitrarily small. In the single delay case, the delay margin can be calculated explicitly without incurring any additional conservatism. In the general case, this condition can be reduced with some (typically small) conservatism to finite-dimensional LMIs. Finally, this approach is also extended to the analysis of ,, performance for linear time-delay systems with an exogenous disturbance. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||