• Proceedings of the KIEE Conference
• /
• 2005.07d
• /
• pp.2723-2725
• /
• 2005

In this paper, a robust $H{\infty}$ stabilization problem to a uncertain discrete-time nonlinear systems with time-delay via fuzzy static output feedback is investigated. The Takagi-Sugeno (T-S) fuzzy model is employed to represent an uncertain nonlinear systems with time-delayed state. Then parallel distributed compensation technique is used for designing of the robust fuzzy controller. Using a single Lyapunov function, the globally asymptotic stability and disturbance attenuation of the closed-loop fuzzy control system are discussed. Sufficient conditions for the existence of robust $H{\infty}$ controllers are given in terms of linear matrix inequalities via similarity transform and congruence transform technique.

• 제어로봇시스템학회:학술대회논문집
• /
• 2005.06a
• /
• pp.1228-1233
• /
• 2005

In this paper, we present a new guidance law for a reusable launch vehicle (RLV) that lands vertically after reentry. In our past studies, a guidance law was developed for a vertical/soft landing to a target point. The guidance law, which is analytically obtained, can regenerate a trajectory against disturbances because it is expressed in the form of state feedback. However, the guidance law does not necessarily guarantee a vertical/soft landing when a dynamical system such as an RLV includes a nonlinear phenomenon owing to the atmosphere of the earth. In this study, we introduce a design of the guidance law for a nonlinear system to achieve a vertical/soft landing on the ground using the exact linearization method and solving the two-point boundary-value problem for the derived linear system. Numerical simulation confirmed the validity of the proposed guidance law for an RLV in an atmospheric environment.

• Proceedings of the KIEE Conference
• /
• 1999.07b
• /
• pp.693-695
• /
• 1999

In this paper, the adaptive nonlinear state observer is proposed to estimate the internal states and the nonlinearities of 4-cylinders 4-cycles spark ignition(SI) engines. The observed states and nonlinearities will be used to design the adaptive feedback linearization controller for reducing the fluctuation of idle speed. The simulation results are represented to show the validity of the proposed nonlinear observer-based adaptive controller.

• Proceedings of the IEEK Conference
• /
• 1999.06a
• /
• pp.1133-1136
• /
• 1999

A magnetic levitation control system is inherently nonlinear and very unstable. Thus there should be a stabilizing compensator network and a negative feedback path using noncontact photoresistor or ultrasonic sensors for the levitation operation. Since the photo sensor plays a key role in the system, the steady-state error and transient performance of the overall system depend on the characteristics of the sensors. But the sensor itself also suffers from nonlinearity, and the magnitude of sensor input heavily depends on environmental conditions. To improve the output performance, we added a linearizing circuit for the sensor characteristics and a disturbance cancelation circuit to avoid sensitive output due to extraneous interfering light.

• Proceedings of the KSR Conference
• /
• 2007.11a
• /
• pp.917-922
• /
• 2007

Electromagnetic suspension, the suspension system used for Maglev trains, is now being applied to urban and inter-city transportation systems, offering environmental benefits. This suspension system is actively controlled to stabilize the suspended vehicle as it runs over an elevated guideway, which, for various reasons, may have deviations in its height. For this reason, frequency responses of the suspension to height deviations must be predicted in the system design cycle. The equations of motion of the electromagnetic suspension employing the 5 state feedback control law are derived for frequency analysis. The results of this paper could be used to determine design requirements for the urban Maglev transportation system currently under development in Korea.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1996.11a
• /
• pp.301-305
• /
• 1996

$\mu$ theory can handle the parametric uncertainty and produces more non-conservative controller than H$_{\infty}$ control theory. However an existing solution of the theory, D-K iteration, creates a controller of huge order and cannot handle the real or mixed real-complex perturbation sets. In this paper, we use genetic algorithms to solve these problems of the D-K iteration method. The Youla parameterization is used to obtain all stabilizing controllers and the genetic algorithms determines the values of the state feedback gain, the observer gain, and Q parameter to minimize $\mu$, the structured singular value, of given system. From an example, we show that this method produces lower order controller which controls a real parameter-perturbed plant than D-K iteration method.

• The Transactions of the Korean Institute of Electrical Engineers D
• /
• v.52 no.4
• /
• pp.205-211
• /
• 2003

In this paper we propose a disturbance design method to test a system's stability. It is shown that the time maximum disturbance is represented in bang-bang and state feedback form. To maximize the time severity index, the value of disturbance is determined by the associated switch curve. The original switch curve is vulnerable to model uncertainties and takes much calculation time. We propose an improved method to approximate the original switch curve. This reduces the computational time and implements sufficiently to test the stable system. Simulation results show how the approximate switch curve can be used to stress a system by driving it to oscillation along the maximum limit cycle.

• The Transactions of the Korean Institute of Electrical Engineers D
• /
• v.55 no.9
• /
• pp.409-413
• /
• 2006

In this paper, we propose a new sliding surface design method for a class of uncertain systems with mismatched unstructured uncertainties. The uncertain system under consideration may have mismatched parameter uncertainties in the state matrix as well as in the input matrix. In terms of linear matrix inequalities (LMIs), we give a sufficient condition for the existence of linear sliding surfaces guaranteeing the asymptotic stability of the sliding mode dynamics. And, we give an LMI parameterization of such linear sliding surfaces together with switched feedback control laws. Our LMI condition can be less conservative than the existing conditions and our result supplement the existing results. Finally, we give a numerical example showing that our method can be better than the previous results.

• Proceedings of the KIEE Conference
• /
• 1996.07b
• /
• pp.1131-1133
• /
• 1996

In this paper, we consider the mixed $L_1/H_{\infty}$ problems of finding internally stabilizing controllers which minimize the peak-to-peak gain of a certain closed loop transfer function with $H_{\infty}$-norm constraint on other closed loop transfer function(or vise versa). This problem is a useful framework for designing a controller with the norm constraints upon time and frequency domain. We formulate the mixed $L_1/H_{\infty}$ problem as LMI problems by using the reachable set. This paper offers the sufficient condition for the existence of suboptimal state feedback controller, and shows that suboptimal solution can be obtained by solving a finite-dimensional convex optimization and a line search.

• Proceedings of the KIEE Conference
• /
• 1996.11a
• /
• pp.454-456
• /
• 1996

This paper deals with the comparison study of speed controller for torsional vibration suppression of 2-mass motor drive system. Firstly conventional methods suggested were classified systematically and the features of each method were also compared. Especially the speed controller based on Kalman filter and LQ state feedback was proposed and the response characteristics of it were compared with those of some other methods. Through various computer simulations and the experiments of real 22[KW] field oriented controlled AC motor drive system having 2-mas mechanical system, it was confirmed that the characteristic of proposed speed controller using Kalman filter and LQ is the best among them.