Aldayr D. de Araujo

Output Feedback Variable Structure Adaptive Control of a Flexible Spacecraft

Abstract Based on the variable structure model reference adaptive control theory, a new control system for the control of an orbiting flexible spacecraft, using output feedback, is designed. The spacecraft consists of a main rigid body to which elastic appendages are attached. For the purpose of control, a moment generating device is located on the rigid hub. For the derivation of control law, it is assumed that the parameters and the structure of the nonlinear functions in the model are unknown. It is shown that in the closed-loop system including the variable structure model reference adaptive control system designed using bounds on uncertain functions, the pitch angle tracks given reference trajectory and the vibration is suppressed. Digital simulation results show that the closed-loop system has good transient behavior and robustness to the uncertainties, unmodeled dynamics, and disturbance inputs.

VARIABLE STRUCTURE ADAPTIVE CONTROL OF WING-ROCK MOTION OF SLENDER DELTA WINGS

Based on the variable structure model reference adaptive control (VS-MRAC) theory, a new control system for the control of wing-rock motion of slender delta wings, using only roll angle measurement, is designed. For the derivation of the control law, it is assumed that the aerodynamic parameters and the structure of the nonlinear aerodynamic nonlinear functions in the model are unknown. Moreover, it is assumed that disturbance input is present in the system. It is shown that in the closed-loop system including the VS-MRAC system designed using bounds on uncertain functions, the roll angle tracks given reference trajectory and the wing-rock motion is suppressed. Digital simulation results show that the closed-loop system has good transient behavior and robustness to the uncertainties and disturbance input.

Asymptotic Reproducibility in Nonlinear Systems and Attitude Control of Gyrostat

A control law is presented for asymptotic function reproducibility in a class of nonlinear-systems such that the output of the system asympotically tends to a given function. The controller consists of a prefilter and a servocompensator. Based on this result, a nonlinear feedback control law for the attitude control of a satellite containing symmetric rotors, in a circular orbit, is derived. In the closed-loop system, given trajectories of pitch, yaw, and roll angles are asymptotically followed, and set point control of attitude is accomplished. Digital simulation results are presented to show the capability of the nonlinear controller.

OUTPUT FEEDBACK ADAPTIVE VARIABLE STRUCTURE CONTROL OF CHAOS IN LORENZ SYSTEM

Based on the variable structure model reference adaptive control (VS-MRAC) theory, a new control system for the control of chaos in Lorenz system, using only the measured output variable, is designed. For the derivation of the control law, it is assumed that the parameters of the model are unknown. Moreover, it is assumed that a disturbance input is present in the system. It is shown that in the closed-loop system, the output variable tracks a given reference trajectory, and the state vector converges to the equilibrium state. Digital simulation results show that the closed-loop system has good transient behavior and robustness to the uncertainties and disturbance input.

Asymptotic Functional Reproducibility and Control of Interconnected Power System

For a class of multivariable non-linear systems, a sufficient condition for the existence of control to generate output which asymptotically tends to a given real analytic vector function is derived. A prefilter (right inverse) is constructed to generate the required control. Based on this result, a control to steer the alert state of an interconnected power system to a secure state is derived. The steering of the state is achieved by controlling the turbine outputs and the field voltages. The controlled rotor angles and generator voltages follow damped sinusoidal and damped polynomial waveforms. The power system attains the desired equilibrium angles of the rotors and deviations in the frequency, tie-line power flows and generator voltages tend to zero as t→∞. Simulation results are presented for a simple power system.

Decoupling of a Synchronous Generator by an Adaptive Model Reference Control Based on Radial Basis Functions

Abstract An alternative nonlinear technique for decoupling and control based on a RBF (Radial Basis Functions) neural network applied to synchronous generator is presented. This technique does not require knowledge of the system and due the nature of radial basis functions, it shows itself stable to parametric uncertainties, disturbances and simpler when it is applied in control. The RBF decoupler is designed in this paper for decouple a nonlinear MIMO system with two inputs and two outputs. The weights between hidden layer and output layer are modified online using an integral law. A decoupling adaptive controller uses the error between reference input, output and filtered outputs to produce control signals to the generator, forcing its outputs to behave like the reference model. Simulation is presented to show the performance of the RBF decoupling. A brief comparison with a decoupling presented by Araujo (1983), using a Hirschorns algorithm to find inverse system and an asymptotic functional reproducibility applied to same nonlinear model of the generator is commented.

Output Feedback Adaptive Variable Structure Control of Chaos in Lorenz System

Abstract Based on the variable structure model reference adaptive control (VS-MRAC) theory, a new control system for the control of chaos in Lorenz systems, using only output measurement, is designed. For the derivation of the control law, it is assumed that the parameters of the nonlinear functions in the model are unknown. Moreover, it is assumed that disturbance input is present in the system. It is shown that in the closed-loop system the output tracks a given reference trajectory and the chaos is suppressed. Numerical simulation results show that the closed-loop system has good transient behavior and robustness to the uncertainties and disturbance input.

Asymptotic Functional Reproducibility and Alert State Steering of Nonlinear Interconnected Power System

For a class of multivariable nonlinear systems a sufficient condition for the existence of control to generate output which asymptotically tends to a given real analytic vector function is derived. A prefilter (right inverse) is constructed to generate the required control. Based on this result, a control to steer the alert state of an interconnected power system to a secure state is derived. The steering of the state is achieved by controlling the turbine outputs and the field voltages. The controlled rotor angles and generator voltages follow damped sinusoidal and damped polynomial waveforms. The power system attains the desired equilibrium angles of the rotors and deviations in the frequency, tie-line power flows and generator voltages tend to zero as t¿¿.