• The Transactions of the Korean Institute of Power Electronics
• /
• v.23 no.5
• /
• pp.321-327
• /
• 2018

DC microgrid system composed of multiple converters has a tendency to make the system unstable due to the interaction of converters. To solve this problem, in this paper, the interaction between cascaded converters with LC input filter is analyzed with impedance modeling using g-parameter. The input impedance and the output impedance of the system can be obtained through this technique. The stability of the system can be determined by applying Middlebrook's stability criterion to the impedance. Virtual impedance is added to the controller to enhance stability. The validity of the analysis is verified by the result of several simulations and experiments.

• 제어로봇시스템학회:학술대회논문집
• /
• 1989.10a
• /
• pp.901-906
• /
• 1989

A robust stability problem for time delay systems is discussed by using a property of Lyapunov type operator equation. We propose a method to check the robust stability against the parameter perturbations occurring in both lumped parameter part and distributed delay element.

• Journal of Advanced Marine Engineering and Technology
• /
• v.25 no.2
• /
• pp.351-356
• /
• 2001

In this paper, a general one-loop control system was assumed as a model system which has a time-delay element connected with a first order-lag element in series. After the corresponding parameter set causing stability limit condition for the model system was obtained by mathematical procedures, their loci on the parameter space was taken according of frequency change,. The parameter set loci of stability limit showed a specific pattern, and particularly the curves on the Kp-Ti parameter space were able to generalized in the form of an exponential formula. These properties were also compared with the results taken from experimental procedures by Nyquist response method and Ziegler & Nichols method on the time domain, and both results were confirmed to be nearly same.

• Bulletin of the Korean Mathematical Society
• /
• v.54 no.4
• /
• pp.1309-1321
• /
• 2017

In this paper, we present a practical Mittag Leffler stability for fractional-order nonlinear systems depending on a parameter. A sufficient condition on practical Mittag Leffler stability is given by using a Lyapunov function. In addition, we study the problem of stability and stabilization for some classes of fractional-order systems.

• 한국데이터정보과학회:학술대회논문집
• /
• 2003.05a
• /
• pp.39-39
• /
• 2003

• Journal of KSNVE
• /
• v.6 no.5
• /
• pp.595-605
• /
• 1996

If the control force designed on the basis of the mathematical model with parameter errors is applied to control the actual system, the closed-loop performance of the actual system will be degraded depending on the degree of the errors, In this study, the effect of parameter errors on the robustness of several natural controls has been analyzed and compared. Every asymptoic stability condition for the natural controls has been derived using Lyapunov approach, and the characteristics of the stability conditions has also been compared. The extent of deviation of the closed-loop performance from the designed one for the natural controls is derived using operator techniques, and evaluated by numerical method. It has been found that the optimal control, acceleration feedback control, and acceleration-position feedback control among the considered natural controls would be robust one with respect to the parameter errors.

• Proceedings of the KIEE Conference
• /
• 1992.07a
• /
• pp.285-287
• /
• 1992

This paper considers the design of robust stabilizing controller of a linear time-invariant digital system subject to variations of parameter vector. For a given controller the radius of the largest stability hypersphere in this parameter space is calculated. This radius is a measure of the stability Margin of the closed-loop system. Based on this calculation a design procedure is proposed to robustify a given stabilizing controller. This algorithm iteratively enlarges the stability hypersphere in parameter space and can be used to design a controller to stabilize a plant subject to given ranges of parameter perturbations. These results are illustrated by an example.

• Journal of Institute of Control, Robotics and Systems
• /
• v.12 no.6
• /
• pp.517-523
• /
• 2006

This paper is focused on a robust saturation controller for the stable linear time-invariant (LTI) system involving both actuator's saturation and structured real parameter uncertainties. Based on affine quadratic stability and multi-convexity concept, a robust saturation controller is newly proposed and the linear matrix inequality (LMI)-based sufficient existence conditions for this controller are presented. The controller suggested in this paper can analytically prescribe the lower and upper bounds of parameter uncertainties, and guarantee the closed-loop robust stability of the system in the presence of actuator's saturation. Through numerical simulations, it is confirmed that the proposed robust saturation controller is robustly stable with respect to parameter uncertainties over the prescribed range defined by the lower and upper bounds.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.2
• /
• pp.630-643
• /
• 1991

The hydrodynamic stability equations are formulated for buoyancy-induced flows adjacent to a vertical, planar, isothermal surface in cold pure water. The resulting stability equations, when reduced to ordinary differential equation by a similarity transformation, constitute a two-point boundary-value(eigenvalue) problem, which was numerically solved for various values of the density extremum parameter R=( $T_{m}$ - $T_.inf./) / ( $T_{o}$ - $T_.inf./). These stability equations have been solved using a computer code designed to accurately solve two-point boundary-value problems. The present numerical study includes neutral stability results for the region of the flows corresponding to 0.0.leq. R. leq.0.15, where the outside buoyancy force reversals arise. The results show that a small amount of outside buoyancy force reversal causes the critical Grashof number $G^*/ to increase significantly. A further increase of the outside buoyancy force reversal causes the critical Grashof number to decrease. But the dimensionless frequency parameter $B^*/ at $G^*/ is systematically decreased. When the stability results of the present work are compared to the experimental data, the numerical results agree in a qualitative way with the experimental data.erimental data.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.2 s.107
• /
• pp.207-213
• /
• 2006

In our previous research, we proposed a robust saturation controller which involves both control input saturation and structured real parameter uncertainties. This controller can analytically prescribed the upper and lower bounds of parameter uncertainties, and guarantee the closed-loop robust stability of the system in the presence of actuator's saturation. And the availability and the effectiveness of the proposed robust saturation controller were verified through numerical simulations. In this paper, we verify the robust stability of this controller through experimental tests. Expecially, we show unstable cases of other controllers in comparison with this controller. Experimental tests are carried out in the laboratory using a two-story test structure with a hydraulic-type active mass damper.