Megumi Matsutani

Design and Verification of an Adaptive Controller for the Generic Transport Model

This paper focuses on the development, implementation, and verification of An Adaptive Control Technology for Safe Flight (ACTS). In particular, we design a controller for the Generic Transport Model (GTM) and evaluate the robustness improvements resulting from adaptation when various uncertainties and failures occur. The ACTS architecture consists of three major components (i) a baseline controller that provides satisfactory performance under nominal flying conditions, (ii) an adaptive controller that accommodates for anomalous flying conditions resulting from uncertainty and failure, and (iii) a nonlinear reference model customized according to the GTM dynamics. While the baseline controller uses anti-wind up devices and a control allocation scheme that correlates inputs of the same class, the adaptive controller accommodates for control saturation and integration wind-up without enforcing any allocation, thereby enabling the generation of independent inputs. The effectiveness of the ACTS controller is studied by evaluating its performance for a set of damages in the aircraft’s structure, and by carrying out control verification studies that evaluate the degradation in closed-loop performance resulting from failures of increasing levels of severity.

Design of an Adaptive Controller for a Remotely Operated Air Vehicle

This paper presents an augmented control architecture for safe flight. This architecture consists of a nominal controller that provides satisfactory performance under nominal flying conditions and a direct model reference adaptive controller that provides robustness to parametric uncertainty. The design, implementation, tuning, and robustness analysis procedures of both the nominal and augmented controllers are presented. The aim of these procedures, which encompass both theoretical and practical considerations, is to develop a controller suitable for flight. The architecture proposed is applied to the NASA generic transport model. This is a model of a transport aircraft for which both a dynamically scaled flight-test article and a high-fidelity simulation are available. A robustness analysis framework, which bounds the set of adverse flying conditions for which all closed-loop requirements are met, indicates some advantages and drawbacks of adaptation. The adverse conditions considered are grouped into four categories: aerodynamic uncertainties, structural damage, unknown time delays, 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 are fast pilot-command tracking, bounded structural loading, satisfactory transient response, bounded flight envelope, and satisfactory handling/riding qualities. A computational approach that integrates this robustness analysis framework and a design-optimization technique is proposed. This approach enables the systematic search for the controller’s parameters that yield the best robustness characteristics allowed by the control structure.

Trustable autonomous systems using adaptive control

A long standing problem in adaptive control is the derivation of robustness properties in the presence of unmodeled dynamics, a necessary and highly desirable property for designing adaptive flight control for systems with trustable autonomy. We provide a solution to this problem in this paper for linear time-invariant plants whose states are accessible for measurement. This is accomplished by using a Lipschitz continuous projection algorithm that allows the utilization of properties of a linear system when the adaptive parameter lies on the projection boundary. This in turn helps remove the restriction on plant initial conditions, as opposed to the currently existing proofs of semi-global stability. A direct implication of this result is the robustness of adaptive control systems to time-delays, and the guarantee that the underlying adaptive system will have a delay margin.

Guaranteed delay margins for adaptive control of scalar plants

Robust adaptive control of scalar plants in the presence of time-delays is established in this paper. It is shown that a standard adaptive controller with a projection algorithm ensures global boundedness of the overall adaptive system for a range of non-zero delays. The upper bound of such delays, i.e. the delay margin, is explicitly computed.

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.

Adaptive Control of Scalar Plants in the Presence of Unmodeled Dynamics

Abstract 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.

Robust Adaptive Control in the Presence of Unmodeled Dynamics: A Counter to Rohrs's Counterexample

Robust adaptive control of general n order plants with a scalar input in the presence of unmodeled dynamics is established in this paper. Recently, it has been 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 including Rohrs’s counterexample. In this paper, we extend this result to higher dimensional plants whose states variables are accessible.

Guaranteed delay margins for adaptive systems with state variables accessible

Robust adaptive control for plants whose state variables are accessible in the presence of time-delays is established in this paper. It is shown that a standard adaptive controller with a projection algorithm ensures global boundedness of the overall adaptive system for a range of non-zero delays. The upper bound of such delays, i.e. the delay margin, is explicitly computed.

An adaptive reset control system for flight safety in the presence of actuator anomalies

This paper addresses the effect of actuator anomalies on flight control design, with particular emphasis on loss of effectiveness and actuator saturation. An adaptive controller with an integral action and a resetting strategy is proposed to address the actuator anomalies.We show that the stability of the closed-loop system can be guaranteed and that the controller allows a graceful degradation of the system performance in the presence of saturation. Simulations of a nonlinear transport aircraft-model are carried out to validate the proposed adaptive controller. The results show that the adaptive reset controller leads to a significantly improved performance compared to a non-adaptive controller.

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.