Siva S. Banda

Toward improvement of tracking performance nonlinear feedback for linear systems

A composite nonlinear feedback tracking control law based on a nominal linear controller is proposed. The design yields nonlinear feedback laws that both increase the speed of the closed-loop system response to the command input and reduce the overshoot, while not imperilling the small signal performance achieved by the nominal linear feedback controller in the face of actuator amplitude saturation. A modern flight control application is used to demonstrate the effectiveness of the design.

Robust multivariable flight control

Manual flight control system design for fighter aircraft is one of the most demanding problems in automatic control. Fighter Aircraft dynamics generally have highly coupled uncertain and nonlinear dynamics. Multivariable control design techniques offer a solution to this problem. Robust Multivariable Flight Control provides the background, theory and examples for full envelope manual flight control system design. It gives a versatile framework for the application of advanced multivariable control theory to aircraft control problems. Two design case studies are presented for the manual flight control of lateral/directional axes of the VISTA-F-16 test vehicle and an F-18 trust vectoring system. They demonstrate the interplay between theory and the physical features of the systems.

Multiple Timescale Flight Control Using Reconfigurable Sliding Modes

Adual-timescaleaircrafte ight-controlproblemisaddressedviacontinuoussliding-modecontrol.Sliding-surface boundary-layer recone guration is used to account for actuator dynamics, dee ection limits, and rate limits. A recone gurable sliding-mode e ight controller is designed that achieves robust, high-accuracy tracking of outerloop command angles before and after damage to an aircraft. Angular rate commands are robustly tracked in an inner loop. The recone gurable e ight-control strategy is based on a continuous sliding-mode controller with direct boundary-layer adaptation for recone guration. On-line explicit system or damage identie cation is not required. Therecone gurablesliding-modee ight-controltechniqueisapplied to anonlineare ight-dynamicsmodelofan F-16 aircraft. Computer simulations demonstrate stability and high-accuracy tracking performance without violation of actuator limits.

Design of Nonlinear Control Laws for High-Angle-of-Attack Flight

High-angle-of-attack flight control laws are developed for a supermaneuvera ble fighter aircraft. The methods of dynamic inversion and structured singular value synthesis are combined into an approach which addresses both the nonlinearity and robustness problems of flight at extreme operating conditions. The primary purpose of the dynamic inversion control elements is to linearize the vehicle response across the flight envelope. Structured singular value synthesis is used to design a dynamic controller which provides robust tracking to pilot commands. The resulting control system achieves desired flying qualities and guarantees a large margin of robustness to uncertainties for high-angle-of-attack flight conditions. High-fidelity nonlinear simulation results show that the combined dynamic inversion /structured singular value synthesis control law achieves a high level of performance in a realistic environment.

Robust flight control design using dynamic inversion and structured singular value synthesis

A direct methodology for the design of flight control systems is introduced. The design approach uses a control selector and an inner/outer loop structure to achieve robustness and performance across the flight envelope. A control selector normalizes control effectiveness with respect to generalized inputs. An inner loop uses dynamic inversion to equalize plant dynamics across the flight envelope. An outer loop is designed around this equalized plant, using mu -synthesis to achieve performance and robustness goals. The methodology is applied to the design of a manual flight control system for the lateral axis of a fighter aircraft. Analysis shows that the inner/outer loop approach produces designs with excellent performance and robustness for a broad range of operating conditions. The direct incorporation of design goals such as flying qualities requirements and the elimination of gain scheduling make this direct methodology an effective and efficient alternative to traditional flight control design approaches. >

Adaptive feedback linearizing nonlinear close formation control of UAVs

This paper deals with the problem of formation flight control of multiple unmanned aerial vehicles (UAVs). In close formation the wing UAV motion is affected by the vortex of the adjacent lead aircraft. In this paper, the vortex forces are treated as unknown functions. An adaptive control law is derived for the position control of the wing aircraft based on a backstepping design technique. In the closed-loop system, commanded separation trajectories are asymptotically tracked by each wing aircraft while the lead UAV is maneuvering. It is seen that an over parametrization in the design is essential for the decentralization of the control system. These results are applied to formation flight control of two UAVs and simulation results are obtained. These results show that the wing UAV follows precisely the reference separation trajectories in spite of the uncertainties in the aerodynamic coefficients, while the lead aircraft is maneuvering.

Bifurcation Stabilization with Local Output Feedback

Local output feedback stabilization with smooth nonlinear controllers is studied for parameterized nonlinear systems for which the linearized system possesses either a simple zero eigenvalue or a pair of imaginary eigenvalues and the bifurcated solution is unstable at the critical value of the parameter. It is assumed that the unstable mode corresponding to the critical eigenvalue of the linearized system is not linearly controllable. Results are established for bifurcation stabilization using output feedback where the critical mode can be either linearly observable or linearly unobservable. The stabilizability conditions are characterized in explicit forms that can be used to synthesize stabilizing controllers. The results obtained in this paper are applied to rotating stall control for axial flow compressors as an application example.

Optimal Feedback Control of Vortex Shedding Using Proper Orthogonal Decomposition Models

We treat the question of control of two-dimensional incompressible, unsteady wake flow behind a circular cylinder at Reynolds number Re = 100. Two finite-dimensional lower order models based on proper orthogonal decomposition (POD) are considered for the control system design. Control action is achieved via cylinder rotation. Linear optimal control theory is used for obtaining stabilizing feedback control systems. An expression for the region of stability of the system is derived. Simulation results for 18-mode POD models obtained using the control function and penalty methods are presented

Input–output invertibility and sliding mode control for close formation flying of multiple UAVs†

This paper treats the question of invertibility of input–output maps and the design of a robust control system for formation flying of multiple unmanned aerial vehicles (UAVs). In close formation, the wing UAV motion is affected by the vortex of the adjacent lead aircraft. The forces produced by these vortices are complex functions of relative position coordinates of the UAVs. In this paper, these forces are treated as unknown functions. For trajectory tracking, invertibility of certain input–output maps in the wind axes system are examined. Interestingly, in the wind axes system, the system is not invertible, but in a simplified co-ordinate system obtained from the wind axes system for which the velocity roll is zero, inverse control of separation co-ordinates is possible. Variable structure control laws are derived for separation trajectory control of wing aircraft in the simplified wind co-ordinate system and for the flight control of the lead aircraft. Simulation results for two UAVs are presented which show precise separation trajectory control in spite of the presence of unknown vortex forces, while the lead aircraft maneuvers. Furthermore, these results confirm that when the wing aircraft is positioned properly in the vortex of the lead aircraft, there is a reduction in the required flight power. Published in 2000 by John Wiley & Sons, Ltd.

Necessary and sufficient conditions for mixed H/sub 2/ and H/sub infinity / optimal control

Mixed H/sub 2/ and H/sub infinity / optimal control problems are addressed. D.S. Bernstein and W.M. Haddad (1989) considered the case of one exogenous input and two observed outputs. Using a Lagrange multiplier technique, and under the assumption that the order of the controller is specified, they derived a necessary condition for minimizing an upper bound of the H/sub 2/ norm of one transfer matrix, subject to an H/sub infinity / norm constraint on the other. J.C. Doyle et al. (1989) later derived a sufficient condition for minimizing what may be shown to be the dual version of the upper bound defined by Bernstein and Haddad (BH) for the mixed H/sub 2/ and H/sub infinity / optimal control problem. In contrast with the BH system, the system of Doyle et al. (DZB) has two exogenous inputs and one measured output. The conditions are derived under different algebraic frameworks. The results are presented of a study that attempts to unify the two mixed optimality conditions. The sufficient condition for the DZB mixed H/sub 2/ and H/sub infinity / full order optimal control is shown to be the dual of the necessary condition for the BH control. Therefore, both conditions are proved to be necessary and sufficient.<<ETX>>