• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.6 s.52
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• pp.93-102
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• 2006

Control input's saturation of active control devices for large structures under large external disturbances are often occurred. It is more difficult to obtain the exact values of mass and stiffness as structures are higher. The modelling errors between mathematical models and real structures must be also included as parameter uncertainties. Therefore, in active vibration control of civil engineering structures like buildings and bridges, the robust saturation controller design method considering both control input's saturation and parameter uncertainties of system is needed. In this paper, stabilities of linear optimal controller LQR, modified bang-bang controller, saturated sliding mode controller, and robust saturation controller among various controllers which have been studied and applied to active vibration control of buildings are investigated. Especially, unstable phenomena of the LQR, the modified bang-bang controller and the saturated sliding mode controller when the control input is saturated or parameter uncertainties exist are presented to show the necessity of the robust saturation controller. The robust stability of the robust saturation controller are shown through a numerical example of a 2DOF linear vibrating system and an experimental test of the two-story structure with an active mass damper (AMD).

• Proceedings of the IEEK Conference
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• 2009.05a
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• pp.326-328
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• 2009

we an autotuning algorithm for PI controller with unknown plant. The proposed algorithm uses a saturation function and time delay element as a test signal. Since the integral element of PI controller reduces a phase margin and amplitude margin in the closed loop system, the closed loop system could be resulted in unstable with PI controller, To avoid unstable in the closed loop system with PI controller, the proposed algorithm identifies one point information in the 3rd quadrant of Nyquist plot with a time delay element. The proposed method improves an accuracy of one point identified information with one saturation function.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.211-224
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• 2019

This paper deals with a nonlinear controller based on saturation functions with variable parameters for set-point regulation and trajectory tracking control of an Autonomous Underwater Vehicle (AUV). In many cases, saturation functions with constant parameters are used to limit the input signals generated by a classical PD (Proportional-Derivative) controller to avoid damaging the actuators; however this abrupt bounded harms the performance of the controller. We, therefore, propose to replace the conventional saturation function, with constant parameters, by a saturation function with variable parameters to limit the signals of a PD controller, which is the base of the nonlinear PD with gravitational/buoyancy compensation and the nonlinear PD + controllers that we propose in this paper. Consequently, the mathematical model is obtained, considering the featuring operation of the underwater vehicle LIRMIA 2, to do the stability analysis of the closed-loop system with the proposed nonlinear controllers using the Lyapunov arguments. The experimental results show the performance of an AUV (LIRMIA 2) for the depth control problems in the case of set-point regulation and trajectory tracking control.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.12
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• pp.1160-1166
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• 2015

This paper proposes a decentralized robust adaptive control scheme for robot manipulators with input torque saturation in the presence of uncertainties. The control system should consider the practical problems that the controller gain coefficients of each joint may be nonlinear time-varying and the input torques applied at each joint are saturated. The proposed robot controller overcomes the various uncertainties and the input saturation problem. The proposed controller is comparatively simple and has no robot model parameters. The proposed controller is adjusted by the adaptation laws and the stability of the control system is guaranteed by the Lyapunov function analysis. Simulation results show the validity and robustness of the proposed control scheme.

• Nuclear Engineering and Technology
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• v.53 no.11
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• pp.3685-3693
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• 2021

This paper presents a disturbance observer-based robust backstepping load-following control (DO-RBLFC) scheme for modular high-temperature gas-cooled reactors (MHTGRs) in the presence of actuator saturation and disturbances. Based on reactor kinetics and temperature reactivity feedback, the mathematical model of the MHTGR is first established. After that, a DO is constructed to estimate the unknown compound disturbances including model uncertainties, external disturbances, and unmeasured states. Besides, the actuator saturation is compensated by employing an auxiliary function in this paper. With the help of the DO, a robust load-following controller is developed via the backstepping technique to improve the load-following performance of the MHTGR subject to disturbances. At last, simulation and comparison results verify that the proposed DO-RBLFC scheme offers higher load-following accuracy, better disturbances rejection capability, and lower control rod speed than a PID controller, a conventional backstepping controller, and a disturbance observer-based adaptive sliding mode controller.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.11
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• pp.1105-1110
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• 2008

In this paper, a saturated LQR controller considering control input's saturation for stable linear time-invariant systems with single control input is studied. Based on Lyapunov stability, two linear matrix inequality sufficient existence conditions for this controller are presented. Through numerical simulations for 2DOF vibrating system, it is confirmed that the saturated LQR controller is stable in the presence of control input's saturation and it is also shown that this controller can be applied to vibrating system practically.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.50 no.7
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• pp.325-331
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• 2001

A dynamic anti-windup method for state delayed control systems with input saturation is considered. Under the assumption that a linear controller has been designed for a state delayed control system based on the existing design technique which shows desirable nominal performance, an additional compensator is incorporated to provide a graceful performance degradation despite of input saturation. By regarding the difference of the controller states in the absence and presence of input saturation as an objective function, the dynamic compensator which minimizes it is determined explicitly. The proposed dynamic compensator is the closed form of plant and controller parameters. The proposed method not only provides graceful performance degradation, but it also guarantees the total stability of resulting systems. An illustrative example is provided to show the effectiveness of the proposed method.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.45 no.6
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• pp.102-107
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• 2008

We propose an autotuning algorithm for PI controller with unknown plant. The proposed algorithm uses a saturation function and time delay element as a test signal. Since the integral element of PI controller reduces a phase margin in the closed loop system, the closed loop system could be resulted in unstable with PI controller. To avoid unstable in the closed loop system with PI controller, the proposed algorithm identifies one point information in the 3rd quadrant of Nyquist plot with a time delay element. The proposed method improves an accuracy of one point identified information with one saturation function. We demonstrate a performance of the proposed method via a simulation.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.4
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• pp.112-122
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• 1999

In realistic control systems the nonlinear saturation attributes of the control actuator due to physical limitations should be taken into account This nonlinear saturation of actuators may cause not only deterioration of the control performance but also a large overshoot during start-up and shut-down. As the overshoot increases the system may become oscillatory unstable. in this paper the supervisor implementation which guarantees good performance for saturation operation and prevents reset wind up is presented, Moreover the sufficient conditions of the stability for saturated system using supervisory control with a dynamic controller are provided in the continuous-time and in the discrete-time domain Numerical example is illustrated to depict the efficiency of supervisory control for a typical satuaurated production-distribution system controlled by a discrete-time dynamic controller and to validate basic results by simulation.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.49 no.4
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• pp.191-200
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• 2000

In practical applications, we frequently encounter the actuator nonlinearity in control systems, and its representative nonlinearity is saturation. A controller designed without considering this saturation nonlinearity is often a source of degradation of performance. To treat the saturation nonlinearity more efficiently, we adopt the multiplicative decomposition and the additive decomposition. Based on these decompositions, we present two controller design methods in the LMI(Linear Matrix Inequality) form that guarantee the L2 gain, from the disturbance to the measured output, is less than or equal to a given value. Finally, we give two examples to show the applicability and usefulness of our results.