Showing papers on "Nyquist plot published in 1981"
1 May 1981
TL;DR: In this paper, the robustness of linear time invariant feedback control systems with respect to model uncertainty is considered using frequency domain criteria, and robustness tests are unified under a common framework based on the nature and structure of model errors.
Abstract: The robustness of the stability of multivariable linear time invariant feedback control systems with respect to model uncertainty is considered using frequency domain criteria. Available robustness tests are unified under a common framework based on the nature and structure of model errors. These results are derived using a multivariable version of Nyquist's stability theorem in which the minimum singular value of the return difference transfer matrix is shown to be the multivariable generalization of the distance to the critical point on a single input, single output Nyquist diagram. Using the return difference transfer matrix, a very general robustness theorem is presented from which all of the robustness tests dealing with specific model errors may be derived. The robustness tests that explicitly utilized model error structure are able to guarantee feedback system stability in the face of model errors of larger magnitude than those robustness tests that do not. The robustness of linear quadratic Gaussian control systems are analyzed.
9 citations
TL;DR: In this paper, the analysis of a single-axis rate gyroscope mounted in a vehicle which is spinning with uncertain angular velocity about the spin axis of the gyro is presented.
Abstract: The analysis of a single-axis rate gyroscope mounted in a vehicle which is spinning with uncertain angular velocity about the spin axis of the gyro is presented. The nonlinearity in the equation of motion of the gimbal is retained. Using circle criterion, it is shown that the gimbal motion is globally asymptotically stable if Nyquist plot of the linear transfer function of the gyro lies in the interior of a certain disk. A simple analytical relation for the selection of gyro parameters for stability is derived.
8 citations
TL;DR: In this article, an original algebra is used to provide bands for the inverse Nyquist plots for a multi-variable control system, which facilitates control system design by reducing the indeterminacy in the information available to the designer.
Abstract: An original algebra is used to provide bands for the inverse Nyquist plots for a multi-variable control system. In general these bands are narrower than Gershgorin bands. This facilitates control system design by reducing the indeterminacy in the information available to the designer. Also the technique can be applied to systems which are not diagonally dominant.
5 citations
TL;DR: In this article, it was shown that this substitution is not always valid in MOSFETs, and that the data obtained by Takagi and van der Ziel can be explained in this manner.
Abstract: According to Nyquist's theorem, in the low frequency limit, the thermal noise voltage spectrum can be written as Sv(f) = 4 kTR. Based on this, we can define, RNyquist = Sc(f)/4 kT as the Nyquist resistance of the sample. We can also define the observed zero bias resistance of a sample as R observed = lim V →o (V/I) (V/I). It is common practice to substitute Robserved for RNyquist in order to estimate the thermal noise. It will be shown that this substitution is not always valid in MOSFETs, and that the data obtained by Takagi and van der Ziel can be explained in this manner.
4 citations
TL;DR: In this article, a particular form of the Nyquist criterion for relative stability is advocated for digital control systems, which is derived without resorting to the use of contours that extend to infinity.
Abstract: A particular form of the Nyquist criterion for relative stability is advocated for digital control systems. Allowed parameter values are read directly from the Nyquist mapping. The criterion is derived without resorting to the use of contours that extend to infinity.
3 citations
TL;DR: In this paper, an alternative generalized Nyquist stability criterion is proposed for L 2 systems, which can be deduced from simple encirclement conditions in the complex plane involving the loci of the eigenvalues of G.
Abstract: An alternative [2] generalized Nyquist stability criterion is proposed for L 2 systems. It is shown that the properties of a system transfer function matrix \hat{G}(s) associated with its invertibility in the restricted space of transfer function matrices can be deduced from simple encirclement conditions in the complex plane involving the loci of the eigenvalues of G .
2 citations