• International Journal of Control, Automation, and Systems
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• v.1 no.4
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• pp.503-510
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• 2003

This paper describes the synthesis of robust and non-fragile $H^{i~}$state feedback controllers for linear varying systems with time delay and affine parameter uncertainties, as well as static state feedback controller with structural uncertainty. The sufficient condition of controller existence, the design method of robust and non-fragile $H^{i~}$static state feedback controller, and the region of controllers satisfying non-fragility are presented. Also, using some change of variables and Schur complements, the obtained conditions can be rewritten as parameterized Linear Matrix Inequalities (PLMIs), that is, LMIs whose coefficients are functions of a parameter confined to a compact set. We show that the resulting controller guarantees the asymptotic stability and disturbance attenuation of the closed loop system in spite of time delay and controller gain variations within a resulted polytopic region.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.498-501
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• 2005

This paper deals with the design and evaluation of the robust controller for a synchronous generator excitation system to improve the steady state and transient stability. The nonlinear characteristics of the system is treated as model uncertainties, and then the robust control techniques are introduced into the power system stability design to take into account these uncertainties at the controller design stage. The performance of the designed controller is examined by extensive non-linear time domain simulation. It is shown that the performance of the robust controller is superior to that of the conventional PI controller. This paper also proposes an improved digital exciter control system for a synchronized generator using a digitally designed controller with database. Results show that the proposed control system manifests excellent control performance compared to existing control systems. It has also been confirmed that it is easy for the proposed control system to implement digital control.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.10 s.103
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• pp.1148-1159
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• 2005

In this paper, the various uncertainties generated in an optical disk drive (ODD) and the robust servo designs considering the uncertainties are studied. First, the brief introduction an ODD and the servo error tolerance of it are discussed. Then, the classifications of uncertainty and the concept of relative stability are introduced. Considering the uncertainty of an ODD, two robust control approaches are applied: (i) mixed sensitivity approach in H$\infty$ control theory for unstructured uncertainty, (ii) QFT for structured uncertainty Finally, the designed controllers are realized by DSP, and these controllers are applied to a commercial DVD-ROM drive. From these experiments, we prove that the designed robust controllers have more good disturbance rejection performance and robustness when it is compared to the conventional lead-lag controller.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.119-121
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• 1997

This paper suggests a design method of the robust model following PD control system using genetic algorithm. This PD control system is designed by applying genetic algorithm with reference model to the optimal determination of proportional and derivative gains that are given by PD servo controller. These proportional and derivative gains are optimized simultaneously in the search domain guaranteeing the robust stability of closed-loop system satisfying different stability margins. The effectiveness of this PD control system is verified by computer simulation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.10
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• pp.3079-3094
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• 1996

Recently, the high-precision vibration attenuation technology becomes the essence fo the seccessful development of high-integrated and ultra-precision industries, and is expected to continue playing a key role in the enhancement of manufacturing technology. Vibration isolation system using an air-spring is widely employed owing to its excellent isolation characteristics in a wide frequency range. It has, however, some drawbacks such as low-stiffness and low-damping features and can be easily excited by exogenous disturbances, and then vibration of table is remained for a long time. Consequently, the need for active vibration control for an air-spring vibration isolation system becomes inevitable. Furthermore, for an air-spring isolation table to be successfully employed in a variety of manufacturing sites, it should have a guaranteed robust performance not only to exogenous disturbances but also to uncertainties due to various equipments which might be put on the table. In this study, an active vibration suppression control system using H.inf. theory is designed and experiments are performed to verify its robust performance. An air-spring vibration isolation table with voice-coil-motors as its actuators is designed and built. The table is modeled as 3 degree-of-freedom system. An active control system is designed based on $H_\infty$control theory using frequency-shaped weighting functions. Analysis on its performance and frequency responce properties are done through numerical simulations. Robust characteristics of$H_\infty$ control on disturbances and model uncertainties are experimentally verified through (i) the transient response to the impact excitation of the table, (ii) the steady-state response to the harmonic excitation, and (iii) the response to the mass change of the table itself. An LQG controller is also designed and its performance is compared with the $H_\infty$ controller.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.75.4-75
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• 2001

This paper designs the robust hybrid controller for the multi degree-of-freedom system having uncertainty caused by modeling error and disturbances. The controlled plant is the construction which has an active dynamic vibration absorber on the top and is excited by the El Centre earthquake at the base. The active controller designed by the LQR(Linear Quadratic Regulator) and H-infinity control theory. The robustness of the hybrid H$\infty$ controller is compared with that of the hybrid LQ controller from computer simulation.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10b
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• pp.81-87
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• 1993

In this paper robust stability conditions are obtained for linear dynamical systems under structured nonlinear time-varying perturbations, using absolute stability theory and the concept of dissipative systems. The conditions are expressed in terms of solutions to linear matrix inequality(LMI). Based on this result, a synthesis methodology is developed for robust feedback controllers with worst-case H$_{2}$ perforrmance via convex optimization and LMI formulation.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1822-1825
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• 2003

A practical range estimator based on the robust Kalman filter is proposed to solve the range estimation problem for surface to air missile(SAM) homing guidance. Apart from the previous works based on the extended Kalman filter(EKF) with bearing only measurement, the proposed scheme makes use of line-of-sight(LOS) rate to ensure the fast convergency at long-range. In this reason, the robust Kalman filter is considered to deal with LOS rate measurement error. The recursive linear structure of proposed filter is easy to implement and make it possible to reduce computational burdens. Moreover, it shows good estimation performance without specific guidance law such as oscillation proportional navigation guidance(OPNG).

• Journal of Institute of Control, Robotics and Systems
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• v.6 no.1
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• pp.25-34
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• 2000

In this paper, we design a H^\infty servo controller for gauge control of tandem cold mill. To improve the performance of the AGC(Aotomatic Gauge Control) system based on the Taylor linearized model of tandem cold mill, the H^\infty servo controller is designed to satisfy robust stability, disturbance attenuation and robust tracking properties. The H^\infty servo controller problem is modified as an usual H^\infty control problem, and the solvability condition of the H^\infty servo problem depends on the solvability of the modified H^\infty control problem. Since this modified problem does not satisfied standard assumptions for the H^\infty control problem, it is solved by an LMI(Linear Matrix Inequality) technique. Consequently, the comparison between the H^\infty servo controller and the existing PID/FF(FeedForward) controller shows the usefulness of this study.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.3
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• pp.84-90
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• 1995

The magnetic levitation system has great advantages, such as little friction, no lubrication no noise and so on. The magnetic levitation system need a stabilizing controller because it is a unstable system in natural. This paper presents the robust stabilizing controller design of the magnetic levitation system. The controller which is designed in this paper by $H_{infty}$ control theory is robust servo controller which has zero offset in spite of the model uncertainties. The validity of controller was investigater through the response simulation. In the future, we will use the result of this study at the actual magnetic levitation system.