• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.04b
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• pp.431-438
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• 2000

The cost function consists of the weighting functions concerning the structural responses to be controlled and the controller capability. Therefore, the control efficiency depends on the characteristics of the weighting functions. The objective of this paper is the comparative study of the time domain control strategies of LQR and LQG and the frequency domain strategy of H₂ by setting the equivalent weighting functions to the all control strategies. As a result of analysis, LQR strategy is found to be more efficient than other strategies in terms of the response reduction. but the control force is found to be a little highter. As LQG can compensate the limitation of LQR that all state variables should be identified, LQG is more acceptable algorithm than LQR. Furthermore LQG shows a good performance both in the response reduction and the control force. Finally H₂ algorithm is employed to illustrate the importance of weighting filters considering the frequency characteristics of the response and the controller. It Is shown that the H₂ algorithm is found to be the most effective one for the response control with a little control force having a low frequency band.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10a
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• pp.208-212
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• 1991

LQG/LTR method cannot applied to nonminimum phase plant. In this paper, we present a new approximation method which guaratee the approximation error equal to zero and exact loop transfer recovery. Zero structure of plant and approximated plant are considered in approximation procedure. It is shown that the properties of plant and approximated plant at pole and zero frequency response are exactly same. It is shown by example that the suggested method can avoide the NMP plant constraint arised in designing LQG/LTR.

• 제어로봇시스템학회:학술대회논문집
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• 1986.10a
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• pp.356-361
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• 1986

This paper presents robustness properties of LQ regulators for input-delayed systems. Using frequency-domain representations, the Kalman inequality concerning the return-difference matrix is derived. The stability margins of LQ regulators are investigated using the Kalman inequality when the open-loop system is stable. In order to obtain stability margins a upper bound of the solution of LQ Riccati equations is derived. Finally, the LQG/LTR method to improve the robustness of LQG regulators is obtained and illustrated with an example.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.04a
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• pp.133-142
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• 1992

A kineamatic nonlinear multivariable laundher is modeled of which the azimoth and elevation axes are drived simultaneously and SISO and MIMO LQG/LTR controllers are designed and evaluated for this system. Also, the suitable command input function is suggested for the desired command following performance and the LQG/LTR control system with disturbances and load variation is evaluated for the entire operating range by computer simulation. It is found that the linear SISO LQG/LTR controller can be used for the kinematic nonlinear multivariable launder in the entire operating range and is effective for disturbance rejection and load variation.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.5-5
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• 2000

Some of Spacecraft's structures are flexible so that a certain expected disturbance can easily excite a low frequency vibration on these structures, having very low natural damping. Such vibration will degrade the performance of the system, which should to be kept in a specific shape or attitude against the undesired vibration, In this paper, LQG/LTR controller is developed using an additional dynamic model to increase the performance of the frequency responses at low frequency area,

• Proceedings of the KIEE Conference
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• 1989.07a
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• pp.121-124
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• 1989

In this thesis, a decomposed LQG/LTR controller is designed for an undersea vehicle. The modellig error which results from decomposition of the original model is considered to the design specification for maintaining the robust stability. The LQG/LTR controller designed with new specification is simulated.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.567-571
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• 1992

A guidance loop of the missile system which uses a command to line of sight(CLOS) guidance law is designed based on LQG theory. In the environment of the severe tracking system noise, the system requires small aerodynamic control fin travel and small miss distance simultaneously. Results from a sample airframe shows good performance against a randomly maneuvering target.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.1028-1033
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• 1992

Loop shaping techniques are developed for the LQG/LTR controller design of singular multivariable sytems. One approach is to use the mode form of plant and the other is to replace the eigenvalues at 0 by ones at .epsilon.(.rarw.0). These two concepts for the target filter loop design are applied to a flight autopilot. And it is shown that these techniques are effective ones for the desired loop-shaping of singular multivariable systems.

• International Journal of Precision Engineering and Manufacturing
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• v.1 no.2
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• pp.24-34
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• 2000

In this paper we propose a controller design method, called Quasi-LQG/$H_{\infty}$/LTR for nonlinear servo systems with hard nonlinearities such as Coulomb friction, dead-zone. Introducing the RIDF method to model Coulomb friction and dead-zone, the statistically linearized system is built. Then, we consider $H_{\infty}$ performance constraint for the optimization of statistically linearized systems, by replacing a covariance Lyapunov equation into a modified Riccati equation of which solution leads to an upper bound of the LQG performance. As a result, the nonlinear correction term is included in coupled Riccati equation, which is generally very difficult to thave a numerical solution. To solve this problem, we use the modified loop shaping technique and show some analytic proofs on LTR condition. Finally, the Quasi-LQG/$H_{\infty}$/LTR controller for a nonlinear system is synthesized by inverse random input describing function techniques (ITIDF). It is shown that the proposed design method has a better performance robustness to the hard nonlinearity than LQG/$H_{\infty}$/LTR method via simulations and experiments for the timing-belt driving servo system that contains the Coulomb friction and dead-zone.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.2
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• pp.67-80
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• 1995

In order to control systems which are dominantly subjected to modeling errors and uncertainties, control strategies must deal with the effect of modeling errors and uncertainties. Since most of control methods based on system mathematical model, such as LQG/LTR method, have been developed mainly focused on stability robustness, they can not smartly improve the transient response disturbed by modeling errors and/or uncertainties. In this research, a fuzzy PID control method is suggested, which can stably improve the transient responses of systems disturbed by modeling errors as well as systems not entirely using mathematical models. So as to assure the effectiveness of suggested control method, computer simulations are accomplished for some example systems, through the comparison of transient responses.