An adaptive control technology for flight safety in the presence of actuator anomalies and damage

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 73-74).The challenge of achieving safe flight comes into sharp focus in the face of adverse conditions caused by faults, damage, or upsets. When these situations occur, the corresponding uncertainties directly affect the safe operation of the aircraft. A technology that has the potential for enabling a safe flight under these adverse conditions is adaptive control. One of the main features of an adaptive control architecture is its ability to react to changing characteristics of the underlying aircraft dynamics. This thesis proposes the building blocks of an adaptable and reconfigurable control technology that ensures safe flight under adverse flight conditions. This technology enables the synthesis of such controllers as well as the systematic evaluation of their robustness characteristics. The field of adaptive control is a mature theoretical discipline that has evolved over the past thirty years, embodying methodologies for controlling uncertain dynamic systems with parametric uncertainties [1, 2, 3, 4, 5, 6]. Through the efforts of various researchers over this period, systematic methods for the control of linear and nonlinear dynamic systems with parametric and dynamic uncertainties have been developed [7, 8, 9, 10, 11, 12]. Stability and robustness properties of these systems in the presence of disturbances, time-varying parameters, unmodeled dynamics, time-delays, and various nonlinearities, have been outlined in the references [4]-[13] as well as in several journal and conference papers over the same period.(cont.) In this thesis, we consider the control of a transport aircraft model that resembles the Generic Transport Model [14]. While the vehicles' geometry and aerodynamic model are those of a C5 aircraft, every other aspect has been made to coincide with the GTM, e.g. anti wind-up logic, time-delay due to telemetry, baseline control structure, low-pass and wash-out filters. We delineate the underlying nonlinear model of this aircraft, and introduce various damages, and failures into this model. An adaptive control architecture is proposed which combines a nominal controller that provides a satisfactory performance in the absence of adverse conditions, and an adaptive controller that is capable of accommodating various adverse conditions including actuator saturation. The specific adverse conditions considered can be grouped into the following three categories, (a) upsets, (b) damages, and (c) actuator failures. Specific cases in (a) include flight upsets in initial conditions of various states including angle of attack, cases in (b) include situations where structural failures cause changes in the location of the Center-of-Gravity (CG)[15], while cases in (c) include situations where symmetric and asymmetric failures in control surfaces and engines occur. These failures include losses in control effectiveness, and locked-in-place control surface deflections. The resilience of the adaptive controller to uncertainty is evaluated for safety using the control verification methodology proposed in [16].(cont.) This methodology enables the determination of ranges of uncertainty for which a prescribed set of closed-loop requirements are satisfied. This thesis studies several one-dimensional uncertainty analyzes for two flight maneuvers that focus on the longitudinal and lateral dynamics. As compared to the baseline controller, the adaptive controller enlarges the region of safe operation by a sizable margin in all but one of the cases considered.by Megumi Matsutani.S.M

Robust adaptive flight control systems in the presence of time delay

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from department-submitted PDF version of thesis.Includes bibliographical references (p. 161-165).Adaptive control technology is a promising candidate to deliver high performance in aircraft systems in the presence of uncertainties. Currently, there is a lack of robustness guarantees against time delay with the difficulty arising from the fact that the underlying problem is nonlinear and time varying. Existing results for this problem have been quite limited, with most results either being local or at best, semi-global. In this thesis, robust adaptive control for a class of plants with global boundedness in the presence of time-delay is established. This class of plants pertains to linear systems whose states are accessible. The global boundedness is accomplished using a standard adaptive control law with a projection algorithm for a range of non-zero delays. The upper bound of such delays, i.e. the delay margin, is explicitly computed. The results of this thesis provide a highly desirable fundamental property of adaptive control, robustness to time-delays, a necessary step towards developing theoretically verifiable flight control systems.by Megumi Matsutani.Ph.D

Design of a Model Reference Adaptive Controller for an Unmanned Air Vehicle

This paper presents the "Adaptive Control Technology for Safe Flight (ACTS)" architecture, which consists of a non-adaptive controller that provides satisfactory performance under nominal flying conditions, and an adaptive controller that provides robustness under off nominal ones. The design and implementation procedures of both controllers are presented. The aim of these procedures, which encompass both theoretical and practical considerations, is to develop a controller suitable for flight. The ACTS architecture is applied to the Generic Transport Model developed by NASA-Langley Research Center. The GTM is a dynamically scaled test model of a transport aircraft for which a flight-test article and a high-fidelity simulation are available. The nominal controller at the core of the ACTS architecture has a multivariable LQR-PI structure while the adaptive one has a direct, model reference structure. The main control surfaces as well as the throttles are used as control inputs. The inclusion of the latter alleviates the pilot s workload by eliminating the need for cancelling the pitch coupling generated by changes in thrust. Furthermore, the independent usage of the throttles by the adaptive controller enables their use for attitude control. Advantages and potential drawbacks of adaptation are demonstrated by performing high fidelity simulations of a flight-validated controller and of its adaptive augmentation

Verification and Tuning of an Adaptive Controller for an Unmanned Air Vehicle

This paper focuses on the analysis and tuning of a controller based on the Adaptive Control Technology for Safe Flight (ACTS) architecture. The ACTS architecture consists of a nominal, non-adaptive controller that provides satisfactory performance under nominal flying conditions, and an adaptive controller that provides robustness under off-nominal ones. A framework unifying control verification and gain tuning is used to make the controller s ability to satisfy the closed-loop requirements more robust to uncertainty. In this paper we tune the gains of both controllers using this approach. Some advantages and drawbacks of adaptation are identified by performing a global robustness assessment of both the adaptive controller and its non-adaptive counterpart. The analyses used to determine these characteristics are based on evaluating the degradation in closed-loop performance resulting from uncertainties having increasing levels of severity. The specific adverse conditions considered can be grouped into three categories: aerodynamic uncertainties, structural damage, and actuator failures. These failures include partial and total loss of control effectiveness, locked-in-place control surface deflections, and engine out conditions. The requirements considered are the peak structural loading, the ability of the controller to track pilot commands, the ability of the controller to keep the aircraft s state within the reliable flight envelope, and the handling/riding qualities of the aircraft. The nominal controller resulting from these tuning strategies was successfully validated using the NASA GTM Flight Test Vehicle

An Adaptive Control Technology for Safety of a GTM-like Aircraft

An adaptive control architecture for safe performance of a transport aircraft subject to various adverse conditions is proposed and verified in this report. This architecture combines a nominal controller based on a Linear Quadratic Regulator with integral action, and an adaptive controller that accommodates actuator saturation and bounded disturbances. The effectiveness of the baseline controller and its adaptive augmentation are evaluated using a stand-alone control veri fication methodology. Case studies that pair individual parameter uncertainties with critical flight maneuvers are studied. The resilience of the controllers is determined by evaluating the degradation in closed-loop performance resulting from increasingly larger deviations in the uncertain parameters from their nominal values. Symmetric and asymmetric actuator failures, flight upsets, and center of gravity displacements, are some of the uncertainties considered

Adaptive Control of Scalar Plants in the Presence of Unmodeled Dynamics

Robust adaptive control of scalar plants in the presence of unmodeled dynamics is established in this paper. It is shown that implementation of a projection algorithm with standard adaptive control of a scalar plant ensures global boundedness of the overall adaptive system for a class of unmodeled dynamics

An adaptive control technology for safety of a GTM-like aircraft

An adaptive control architecture for safe performance of a transport aircraft subject to various adverse conditions is proposed and verified herein. This architecture combines a nominal controller based on an LQR with integral action, and an adaptive controller that accommodates for actuator saturation and bounded disturbances. The effectiveness of the baseline controller and its adaptive augmentation are evaluated and compared using a stand-alone control verification methodology. Several failure modes, where an uncertain parameter and a correspondingly critical flight maneuver are paired, are studied. The resilience of the controllers is determined by evaluating the degradation in closed-loop performance that results from increasingly larger uncertainties. Symmetric and asymmetric actuator failures, flight upsets, and CG movements, are some of the uncertainties considered.United States. National Aeronautics and Space Administration (IRAC project, NRA NNH07ZEA001N