A nonlinear harmonic disturbance observer for nonlinear systems subject to harmonics is designed and stability of the proposed observer is established using passivity approach. A systematic procedure to choose the nonlinear gain function in the observer is proposed. The proposed nonlinear disturbance observer can be integrated with a linear/nonlinear controller to improve its disturbance attenuation ability for nonlinear systems under harmonics.

Harmonic Disturbance Observer for Nonlinear Systems

The design of the control of an aircraft encountering windshear after takeoff is treated as a problem of minimizing the H, gain between the windshear and the vertical acceleration of the aircraft. The theory of state feedback H, control of nonlinear systems is given. Both linear and nonlinear controllers are found and the simulations under certain windshear model are carried out.

Flight Control in a Windshear via Nonlinear H, Methods *

Considers the problem of controlling a discrete-time linear system by output feedback so as to have a second output z/sub t/ track an observed reference signal r/sub t/. The authors turn to an approach to the tracking problem, which allows for damping of other system and control variables, and this is our main result. The measure of performance is given by a natural quadratic cost function. The object is to design an optimal regulator which is universal in the sense that it does not depend on the unknown amplitudes and phases of r/sub t/ and w/sub t/ and is optimal for all choices of r/sub t/ and w/sub t/. The authors prove that an optimal universal regulator exists in a wide class of stabilizing and possibly nonlinear regulators under natural technical conditions and that this regulator is in fact linear, provided that the second dimensionality condition above is satisfied. On the other hand, if it is not satisfied, the existence of an optimal universal regulator is not a generic property, so as a rule no optimal universal regulator exists.

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Universal regulators for optimal tracking in discrete-time systems affected by harmonic disturbances

Robust control which is designed via the Lyapunov approach has been shown to be effective for nonlinear uncertain systems. The performance of the controlled systems is studied by the Lyapunov argument. We propose to use the comparison principle which is based on the differential inequality to further explore the performance of controlled uncertain systems.

Performance analysis of controlled uncertain systems

The design of the control of an aircraft encountering windshear after takeoff is treated as a problem of stabilizing the climb rate about a desired value of the climb rate. The resulting controller is a feedback one utilizing only climb rate information. Its robustness vis-a-vis windshear structure and intensity is illustrated via simulations employing four different windshear models.

Aircraft control for flight in an uncertain environment: takeoff in windshear

The design of the control of an aircraft encountering windshear after takeoff is treated as a problem of stabilizing the climb rate about a desired value of the climb rate. The resulting controller is a feedback one utilizing only climb rate information. Its robustness namely windshear structure and intensity is illustrated via simulations employing four different windshear models. The simulations were carried out for the Boeing 727 aircraft. >

Aircraft control under conditions of windshear

The control of an aircraft encountering windshear after takeoff is treated as a problem of stabilizing the climb rate about a desired value. An adaptive strategy is developed which uses only climb rate information. Robustness vis a vis windshear structure and intensity is illustrated via simulations employing four different windshear models.

Adaptive control of aircraft in windshear

A class of nonlinear uncertain dynamical systems that do not satisfy the matching conditions is considered. This class of mismatched systems is more general than one considered earlier. A sufficient condition, in terms of a critical mismatch threshold, which ensures global practical stability, is given. >

A controller for a class of mismatched uncertain systems

The control of an aircraft encountering windshear after takeoff is treated as a problem of stabilizing the climb rate about a desired value. An adaptive strategy is developed which uses only climb rate information. Robustness vis-a-vis windshear structure and intensity is illustrated via simulations employing four different windshear models. Simulations were carried out for a Boeing-727 aircraft with three JT8D-17 turbofan engines. >

S. Pandey

Papers

Aircraft control for flight in an uncertain environment: takeoff in windshear

Aircraft control under conditions of windshear

Adaptive control of aircraft in windshear

A controller for a class of mismatched uncertain systems

Adaptive control of aircraft in windshear