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Nonlinear H (nonlinear + h)

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Selected Abstracts

Adaptive controller design and disturbance attenuation for SISO linear systems with zero relative degree under noisy output measurements

INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 4 2010
Sheng Zeng
Abstract In this paper, we present robust adaptive controller design for SISO linear systems with zero relative degree under noisy output measurements. We formulate the robust adaptive control problem as a nonlinear H, -optimal control problem under imperfect state measurements, and then solve it using game theory. By using the a priori knowledge of the parameter vector, we apply a soft projection algorithm, which guarantees the robustness property of the closed-loop system without any persistency of excitation assumption of the reference signal. Owing to our formulation in state space, we allow the true system to be uncontrollable, as long as the uncontrollable part is stable in the sense of Lyapunov, and the uncontrollable modes on the j,-axis are uncontrollable from the exogenous disturbance input. This assumption allows the adaptive controller to asymptotically cancel out, at the output, the effect of exogenous sinusoidal disturbance inputs with unknown magnitude, phase, and frequency. These strong robustness properties are illustrated by a numerical example. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Explicit constructions of global stabilization and nonlinear H, control laws for a class of nonminimum phase nonlinear multivariable systems

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 12 2008
Weiyao Lan
Abstract This paper investigates a global stabilization problem and a nonlinear H, control problem for a class of nonminimum phase nonlinear multivariable systems. To avoid the complicated recursive design procedure, an asymptotic time-scale and eigenstructure assignment method is adopted to construct the control laws for the stabilization problem and the nonlinear H, control problem. A sufficient solvability condition is established onthe unstable zero dynamics of the system for global stabilization problem and nonlinear H, control problem, respectively. Moreover, based on the sufficient solvability condition, an upper bound of the achievable L2 -gain is estimated for the nonlinear H, control problem. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Robust nonlinear ship course-keeping control by H, I/O linearization and , -synthesis

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 1 2003
Shr-Shiung Hu
Abstract In this paper, the H, input/output (I/O) linearization formulation is applied to design an inner-loop nonlinear controller for a nonlinear ship course-keeping control problem. Due to the ship motion dynamics are non-minimum phase, it is impossible to use the ordinary feedback I/O linearization to resolve. Hence, the technique of H, I/O linearization is proposed to obtain a nonlinear H, controller such that the compensated nonlinear system approximates the linear reference model in I/O behaviour. Then a , -synthesis method is employed to design an outer-loop robust controller to address tracking, regulation, and robustness issues. The time responses of the tracking signals for the closed-loop system reveal that the overall robust nonlinear controller is able to provide robust stability and robust performance for the plant uncertainties and state measurement errors. Copyright © 2002 John Wiley & Sons, Ltd. [source]

H, control for nonlinear affine systems: a chain-scattering matrix description approach

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 4 2001
Jang-Lee Hong
Abstract This paper combines an alternative chain-scattering matrix description with (J, J,)-lossless and a class of conjugate (,J, ,J,)-lossless systems to design a family of nonlinear H, output feedback controllers. The present systems introduce a new chain-scattering setting, which not only offers a clearer expression for the solving process of the nonlinear H, control problem but also removes the fictitious signals introduced by the traditional chain-scattering approach. The intricate nonlinear affine control problem thus can be transformed into a simple lossless network and is easy to deal with in a network-theory context. The relationship among these (J, J,) systems, L2 -gain, and Hamilton,Jacobi equations is also given. Block diagrams are used to illustrate the central theme. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Three-dimensional nonlinear H, guidance law

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 2 2001
Ciann-Dong Yang
Abstract This paper proposes a novel three-dimensional missile guidance law design based on nonlinear H, control. The complete nonlinear kinematics of pursuit,evasion motion is considered in the three-dimensional spherical co-ordinates system; neither linearization nor small angle assumption is made here. The nonlinear H, guidance law is expressed in a simple form by solving the associated Hamilton,Jacobi partial differential inequality analytically. Unlike adaptive guidance laws, the implement of the proposed robust H, guidance law does not require the information of target acceleration, while ensuring acceptable interceptive performance for arbitrary target with finite acceleration. The resulting pursuit,evasion trajectories for both the H, -guided missile and the worst-case target are determined in closed form, and the performance robustness against variations in target acceleration, in engagement condition, and in control loop gain, is verified by numerical simulations. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Robustness improvement of a nonlinear H, controller for robot manipulators via saturation functions

JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 8 2005
Manuel G. Ortega
In this paper, previous works on nonlinear H, control for robot manipulators are extended. In particular, integral terms are considered to cope with persistent disturbances, such as constant load at the end-effector. The extended controller may be understood as a computed-torque control with an external PID, whose gain matrices vary with the position and velocity of the robot joints. In addition, in order to increase the controller robustness, an extension of the algorithms with saturation functions has been carried out. This extension deals with the resulting nonlinear equation of the closed-loop error. A modified expression for the required increment in the control signal is provided, and the local closed-loop stability of this approach is discussed. Finally, simulation results for a two-link robot and experimental results for an industrial robot are presented. The results obtained with this technique have been compared with those attained with the original controllers to show the improvements achieved by means of the proposed method. © 2005 Wiley Periodicals, Inc. [source]