Longitudinal-control design approach for high-angle-of-attack aircraft

This paper describes a control synthesis methodology that emphasizes a variable-gain output feedback technique that is applied to the longitudinal channel of a high-angle-of-attack aircraft. The aircraft is a modified F/A-18 aircraft with thrust-vectored controls. The flight regime covers a range up to a Mach number of 0.7; an altitude range from 15,000 to 35,000 ft; and an angle-of-attack (alpha) range up to 70 deg, which is deep into the poststall region. A brief overview is given of the variable-gain mathematical formulation as well as a description of the discrete control structure used for the feedback controller. This paper also presents an approximate design procedure with relationships for the optimal weights for the selected feedback control structure. These weights are selected to meet control design guidelines for high-alpha flight controls. Those guidelines that apply to the longitudinal-control design are also summarized. A unique approach is presented for the feed-forward command generator to obtain smooth transitions between load factor and alpha commands. Finally, representative linear analysis results and nonlinear batch simulation results are provided

Global Stabilization of Triangular Systems with Time-Delayed Dynamic Input Perturbations

A control design approach is developed for a general class of uncertain strict-feedback-like nonlinear systems with dynamic uncertain input nonlinearities with time delays. The system structure considered in this paper includes a nominal uncertain strict-feedback-like subsystem, the input signal to which is generated by an uncertain nonlinear input unmodeled dynamics that is driven by the entire system state (including unmeasured state variables) and is also allowed to depend on time delayed versions of the system state variable and control input signals. The system also includes additive uncertain nonlinear functions, coupled nonlinear appended dynamics, and uncertain dynamic input nonlinearities with time-varying uncertain time delays. The proposed control design approach provides a globally stabilizing delay-independent robust adaptive output-feedback dynamic controller based on a dual dynamic high-gain scaling based structure.Comment: 2017 IEEE International Carpathian Control Conference (ICCC

Application of variable-gain output feedback for high-alpha control

A variable-gain, optimal, discrete, output feedback design approach that is applied to a nonlinear flight regime is described. The flight regime covers a wide angle-of-attack range that includes stall and post stall. The paper includes brief descriptions of the variable-gain formulation, the discrete-control structure and flight equations used to apply the design approach, and the high performance airplane model used in the application. Both linear and nonlinear analysis are shown for a longitudinal four-model design case with angles of attack of 5, 15, 35, and 60 deg. Linear and nonlinear simulations are compared for a single-point longitudinal design at 60 deg angle of attack. Nonlinear simulations for the four-model, multi-mode, variable-gain design include a longitudinal pitch-up and pitch-down maneuver and high angle-of-attack regulation during a lateral maneuver

Output Feedback Variable Structure Control Design for Uncertain Nonlinear Lipschitz Systems

This paper develops a full-order compensator-based output feedback variable structure control law for uncertain nonlinear Lipschitz systems having matched perturbations. Given that the sufficient condition is satisfied, the developed control scheme, with the observer-like technique incorporated into the design of the compensator, can achieve global exponential stabilization. An illustrative example is provided with simulation results to show the effectiveness of the proposed method

Observer-based strict positive real (SPR) switching output feedback control

This paper considers switching output feedback control of linear systems and variablestructure systems. Theory for stability analysis and design for a class of observer-based feedback control systems is presented. It is shown how a circlecriterion approach can be used to design an observerbased state feedback control which yields a closedloop system with speci ed robustness characteristics. The approach is relevant for variable structure system design with preservation of stability when switching feedback control or sliding mode control is introduced in the feedback loop. It is shown that there exists a Lyapunov function valid over the total operating range and this Lyapunov function has also interpretation as a storage function of passivity-based control and a value function of an optimal control problem. The Lyapunov function can be found by solving a Lyapunov equation. Important applications are to be found in hybrid systems with switching control and variable structure systems with high robustness requirements

Nonlinear and adaptive control systems for underwater and air vehicles

This thesis considers the design of nonlinear and adaptive control systems for the control of submersibles as well as aircraft. In the first part of the thesis, control of submersibles using bow and stern hydroplanes is considered, and (i) a robust output feedback nonlinear control law using modeling error compensation, (ii) a nonlinear adaptive state feedback law using SDU decomposition; and (iii) an output feedback linear adaptive law for the dive-plane maneuvering are derived. The robust nonlinear controller with high-gain observer is designed for depth and pitch angle tracking along constant trajectories in the presence of parametric uncertainties and disturbances due to the sea waves. Next, the adaptive backstopping controller is developed to accomplish depth and pitch angle tracKing SDU decomposition of the high-frequency gain matrix is done to prevent singularity in the control law. For this design, one needs to know the sign of the two minors of the input matrix, but no other knowledge of the submarine parameters is required. Finally, a Model Reference Adaptive Control (MRAC) law using output feedback is derived for the linear model of the submersible; In the second part of the thesis (i) an adaptive Variable Structure flight Control (VSC) system and (ii) an adaptive flight control system for the roll-coupled maneuvers of aircraft using the aileron, rudder and elevator inputs are derived. Again, the SDU decomposition of the high frequency gain matrix is used for the derivation of singularity free control laws. Simulations performed for the underwater and the air vehicles using Matlab and Simulink show that in the closed-loop system, desired trajectory tracking is accomplished using each of the control systems

Energy-based Stabilization of Network Flows in Multi-machine Power Systems

This paper considers the network flow stabilization problem in power systems and adopts an output regulation viewpoint. Building upon the structure of a heterogeneous port-Hamiltonian model, we integrate network aspects and develop a systematic control design procedure. First, the passive output is selected to encode two objectives: consensus in angular velocity and constant excitation current. Second, the non-Euclidean nature of the angle variable reveals the geometry of a suitable target set, which is compact and attractive for the zero dynamics. On this set, circuit-theoretic aspects come into play, giving rise to a network potential function which relates the electrical circuit variables to the machine rotor angles. As it turns out, this energy function is convex in the edge variables, concave in the node variables and, most importantly, can be optimized via an intrinsic gradient flow, with its global minimum corresponding to angle synchronization. The third step consists of explicitly deriving the steady-state-inducing control action by further refining this sequence of control-invariant sets. Analogously to solving the so called regulator equations, we obtain an impedance-based network flow map leading to novel error coordinates and a shifted energy function. The final step amounts to decoupling the rotor current dynamics via feedback-linearziation resulting in a cascade which is used to construct an energy-based controller hierarchically.Comment: In preparation for MTNS 201

Robust sliding mode‐based extremum‐seeking controller for reaction systems via uncertainty estimation approach

"This paper deals with the design of a robust sliding mode‐based extremum‐seeking controller aimed at the online optimization of a class of uncertain reaction systems. The design methodology is based on an input–output linearizing method with variable‐structure feedback, such that the closed‐loop system converges to a neighborhood of the optimal set point with sliding mode motion. In contrast with previous extremum‐seeking control algorithms, the control scheme includes a dynamic modelling‐error estimator to compensate for unknown terms related with model uncertainties and unmeasured disturbances. The proposed online optimization scheme does not make use of a dither signal or a gradient‐based optimization algorithm. Practical stabilizability for the closed‐loop system around to the unknown optimal set point is analyzed. Numerical experiments for two nonlinear processes illustrate the effectiveness of the proposed robust control scheme.

Analysis and synthesis of SISO H[subscript infinity] controllers

Classical feedback control theories are traditionally concerned with issues like stability and performance, however, they typically fail to address issues such as robustness and plant perturbation. This thesis is concerned with the robust stability and the robust performance of single-input single-output plants. The basic issue under analysis is how to realize the benefits of the usual feedback control structure in the presence of model uncertainty. This is accomplished by seeking feedback controllers providing robust stability and performance by minimizing weighted sensitivity functions of a linear system represented by its transfer function. A characterization of models for plants with unstructured uncertainty is introduced. Specifications and measures of stability and performance for robust controllers and the necessary and sufficient conditions to test the robust stability and the robust performance conditions of a control design are explored. A parametrization of feedback controllers that guarantee closed loop stability for both stable and unstable plants is shown and a systematic procedure for synthesizing robust controllers, known in the literature as HK controllers, is presented. These systematic algorithms are based on the theory of interpolation by analytic functions and the solution to the model matching problem. A case study of the inverted pendulum positioning system is developed to illustrate the concepts of robust analysis and the design algorithms. The controller is compared to a classic state variable feedback solution

Application of the Correlation Method to the Tuning of Industrial Control Schemes.

The correlation method of finding a system\u27s impulse response weights, based on the Wiener-Hopf integral, was studied for its application to the tuning of feedback, feedforward, and decoupling control elements in closed loop operation using only ordinary operating data. Also included in the work is a thorough study of actual data for eight typical stochastic disturbances taken from a refinery light ends unit. A disturbance signal typical of these actual signals was used throughout the tuning studies to make results obtained more practically meaningful. These actual signals were also used to demonstrate the desirability of differencing input and output data prior to use of the correlation method. The correlation method was applied to the tuning of feedback and decoupling controllers by using it to find the closed loop impulse response of a system\u27s output to set point changes. Given knowledge of the control structure and control elements, equations are derived which use this closed loop response to obtain the open loop impulse response. Many existing methods are available to design feedback controllers or decouplers given open loop responses. The correlation method was applied to the tuning of feedforward controllers by finding the closed loop impulse response of the system\u27s output to disturbance changes. Equations are derived which convert this closed loop response directly into an improved feedforward controller given the control structure and control elements. An approximation of the manipulated variable transfer function is also required. The equations derived for both problems are applicable to a 2 x 2 interactive process such as a distillation column with or without feedback elements, feedforward controllers, and partial or simplified decouplers. Less complex processes and/or control schemes allow the equations to be significantly simplified. A criterion called the Impulse Confidence Ratio (ICR) is proposed which when interpreted properly will allow the determination of the value of a test result. The correlation method of impulse response determination and the tuning techniques were subjected to numerous tests of robustness in the face of various non-ideal situations which might be expected to arise in real application. The tuning techniques are applied successfully to a nonlinear distillation column model