IEEE Transactions on Circuits and Systems I: Fundamental Theory and Applications

This paper deals with the robust mixed H/sub 2//H/sub /spl infin// filtering problem with regional pole assignment for linear uncertain discrete-time systems in the presence of two sets of exogenous disturbance inputs. A general framework for solving this problem is established using a linear matrix inequality (LMI) approach in conjunction with regional pole constraints, and H/sub 2/ and H/sub /spl infin// optimization characterization. Necessary and sufficient conditions for the solvability of the problem are given in terms of a set of feasible LMIs. A numerical example is provided to illustrate the effectiveness of the proposed design algorithm.

This work reviews and elaborates a frequency domain approximate method of estimating amplitude, frequency, and stability of the limit cycle near Hopf bifurcations. A new iterative method and new criterion for ascertaining stability are presented. The method and criterion are applied to a 3-bus dynamic power system model to give the amplitude, frequency and stability at its Hopf bifurcations. New analytic formulas for bifurcation curves are derived by using analytic method, some new saddle-node bifurcation at low voltage levels are found on the formulas. The influence of rotor inertia on the Hopf bifurcation is also studied.

A nonlinear analysis of an LC oscillator based on an operational transconductance amplifier (OTA), or on a current feedback operational amplifier (CFOA), is presented. Contrary to the usual linear analysis which shows that oscillators based on OTA or CFOA have the same behavior, it is shown that, in fact, they work in a very different manner. SPICE and experimental results which confirm the theoretical analysis are given.

In this paper, we examine how varying the generation redispatch can improve the system stability margins with respect to Hopf bifurcations, as well as robustness to uncertainties in load modeling and distribution. It is seen that an optimal selection of load following units plays a key role in accomplishing these objectives. An optimal redispatch strategy is proposed, and is verified through a variety of experiments on the IEEE 39-bus system.

This paper presents a sufficient condition for the uniqueness and global asymptotic stability of the equilibrium point for delayed cellular neural networks. This result improves and generalizes some of the previous stability results derived in the literature.

This paper presents a fuzzy filtered-U algorithm for an active noise control (ANC) system. Instead of complex designing procedures, the proposed approach uses few mathematical transfer functions to design the ANC system. A fuzzy-based self-tuning algorithm is also provided in this paper to adjust the free parameters of the fuzzy filtered-U algorithm. In addition, the proposed method protects ANC systems against unstable poles such as occur in conventional filtered-U design. Finally, direct numerical simulations through the applications of duct noise demonstrate the effectiveness of the scheme.

A novel idea, a phase-negative feedback for fundamentally injected LC oscillators, is discussed, and a new method of linear approximation of their shortened equations has been presented.

The analysis of synchronous commutations in switching converters is discussed in this paper. The Compensation Theorem (CT) is applied in order to define two matrices, called respectively zero-order and first-order master-slave connection matrix (Z-MSCM, F-MSCM), which allow a unified analysis of both hard and soft synchronous commutations in switching converters. The Z-MSCM and F-MSCM provide the analytical basis for studying the interactions among switching devices in any type of switching converter. The method is presented in its general formulation, valid for the analysis of switching converters including feedback circuitry and soft-switching cells. The examples presented show that the CT-based analysis of commutations is a useful and efficient tool for the comprehension of the mechanisms of synchronous commutations in switching converters and for numerical simulations.

This work investigates the use of prior knowledge in the parameter estimation of NARMAX polynomial models. The problem of parameter estimation is then formulated in such a way that the estimated models have specified features. This formulation results in a constrained optimization problem, which is solved using the ellipsoid algorithm. This technique is applied to a real DC-DC buck converter. In this system, the static relation is known from the theory but identification data are located over a rather narrow range around an operating point. Although obtained from dynamical data, the models provide good approximation to the nonlinear static function.

This paper studies the problem of robust absolute stability of a class of nonlinear discrete-time systems with time-varying matrix uncertainties of polyhedral type and multiple time-varying sector nonlinearities. By using the variational method and the Lyapunov second method, criteria for robust absolute stability are obtained in different forms for the class of systems under consideration. Specifically, we determine the parametric classes of Lyapunov functions which define the necessary and sufficient conditions of robust absolute stability. We apply the piecewise-linear Lyapunov functions of the infinity vector norm type to derive an algebraic criterion for robust absolute stability in the form of solvability conditions of a set of matrix equations. Some simple sufficient conditions of robust absolute stability are given which become necessary and sufficient for several special cases. An example is presented as an application of these results to a specific class of systems with time-varying interval matrices in the linear part.