Actuator Rate Limits Research Articles

Plantwide Control Design Based on the Control Allocation Approach

In this work the control allocation (CA) philosophy is considered in order to propose a plantwide control (PWC) design methodology. For medium/large-scale processes for which the number of actuators is greater than the number of controlled variables, a CA-based strategy can be used to distribute the total control effort among the actuators, with some attractive features. First, the CA module can explicitly handle (i) constraints on inputs (typically actuator position and rate limits) and (ii) additional control objectives (e.g., to penalize the actuators control energy). Second, CA has the potential to provide (actuator) fault tolerance without considering a control structure reconfiguration. In this paper, a decentralized control structure is proposed for computing the total control effort, which is implemented with conventional single-input single-output PID controllers. In addition, a CA module is configured and two alternative algorithms are compared, namely, (i) generalized inverse plus simple satura...

Flight-Test Evaluation of an Adaptive Controller for Flying Qualities Specification and Protection

The human pilot is a crucial component of the pilot/vehicle system. This article focuses on the in-flight ability of an adaptive receding horizon optimal controller to specify favorable flying qualities. Moreover, in the case of a deteriorated vehicle, the controller serves to protect the desirable flying qualities by automatically compensating for the new aircraft characteristics. Although the receding horizon optimal controller is able to protect the handling qualities as long as adequate physical control authority exists, particularly severe failures can result in heavily limited authority where encounters with actuator rate limits may occur. The controller itself is robust to rate-limit encounters, however, the handling qualities suffer because the authority no longer exists to deliver the performance expected by the pilot. To protect handling qualities and mitigate the risk of pilot-induced oscillation past this exhaustion of control authority, the controller is integrated into the Smart Adaptive Flight Effective Cue system (detailed elsewhere). The piloted flight tests demonstrate the capability of the receding horizon optimal controller to 1) deliver specified flying qualities, 2) protect those flying qualities in failure cases where adequate authority exists, and 3) operate in tandem with the Smart Adaptive Flight Effective Cue system to protect the pilot/vehicle system in cases of severely limited authority.

線形参照モデルを用いた速度飽和を含むシステムの安定化

Actuator rate saturation has characteristics to increase the phase lag of the system and it can be one of the factors that destabilize the motion control system for a higher control response. We propose a new control method that can stabilize the system with rate limited actuators. First, it is shown that the actuator rate limited characteristics causes control systems to be unstable using both describing function analysis and nonlinear simulations. Next, the proposed method using linear actuator reference model is described. It can avoid the rate saturation of actuators to improve the phase lag characteristics. Then, the effectiveness of proposed method is demonstrated through stability analysis and nonlinear simulations.

Piloted Evaluation of a Control Allocation Technique to Recover from Pilot-Induced Oscillations

This paper describes the maturation of a control allocation technique designed to assist pilots in recovery from pilot-induced oscillations. The control allocation technique to recover from pilot-induced oscillations is designed to enable next-generation high-efficiency aircraft designs. Energy-efficient next-generation aircraft require feedback control strategies that will enable lowering the actuator rate limit requirements for optimal airframe design. A common issue on aircraft with actuator rate limitations is they are susceptible to pilot-induced oscillations caused by the phase lag between the pilot inputs and control surface response. The control allocation technique to recover from pilot-induced oscillations uses real-time optimization for control allocation to eliminate phase lag in the system caused by control surface rate limiting. System impacts of the control allocator were assessed through a piloted simulation evaluation of a nonlinear aircraft model in the NASA Ames Research Center’s Vertical Motion Simulator. Results indicate that the control allocation technique to recover from pilot-induced oscillations helps reduce oscillatory behavior introduced by control surface rate limiting, including the pilot-induced oscillation tendencies reported by pilots.

Semi‐global leader‐following consensus of multiple linear systems with position and rate limited actuators

SummaryThis paper studies the semi‐global leader‐following consensus problem for a group of linear systems in the presence of both actuator position and rate saturation. Each follower agent in the group is described by a general linear system subject to simultaneous actuator position and rate saturation. For each follower agent, we construct both a linear state feedback control law and a linear output feedback control law by using low gain approach. We show that semi‐global leader‐following consensus can be achieved by using these control laws when the communication topology among follower agents is a connected undirected graph, and the leader is a neighbor of at least one follower. Simulation results illustrate the theoretical results. Copyright © 2014 John Wiley & Sons, Ltd.

A Nonlinear Controller for Input Amplitude and Rate Constrained Linear Systems

This technical note presents a nonlinear state feedback controller for systems with linear dynamics subject to an amplitude and rate limited actuator. The nonlinear state feedback facilitates faster convergence compared to linear state feedback while guaranteeing domains of attraction of similar size. The parametrization of the controller is done solving a convex optimization problem based on linear matrix inequalities (LMIs). Finally, an example illustrates that the controller achieves large stability regions and short settling times.

Design Tradeoffs of Wind Turbine Preview Control

Recent work demonstrated the benefits of preview wind measurements for turbine control. This paper investigates the basic design tradeoffs between turbine performance, preview time, and pitch actuator rate limits. A Region 3 rotor-speed tracking problem is formulated in continuous-time as an optimal control problem using a simple one-state rigid body turbine model. The exact analytical solution to this problem provides insight into the fundamental performance limits. These analytical results are compared with the performance of an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> preview controller simulated on a higher fidelity, nonlinear turbine model with realistic wind sensor models. The performance versus preview time characteristics of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> controllers are in agreement with the predictions from the lower fidelity model. Thus, the analytical results obtained with the low-order model can provide design guidelines for the use of preview information in turbine control.

Dealing with actuator rate limits. Towards IQC-based analysis of aircraft-pilot system stability

The study continues the recent work of the authors, by sketching an approach of the aircraft-pilot system stability analysis, considering both the rate saturation of the actuator and the time delay in control input. A stable behavior of the closed loop pilot-aircraft system with input delay was previously obtained. The problem is now if this stability survives in the presence of the actuator rate saturation. The mathematical tools of stability analysis are those of the Integral Quadratic Constraints (IQC) methodology.

Decentralized control of nonlinear interconnected systems under both amplitude and rate saturations

In this paper, we design a decentralized controller for a class of nonlinear interconnected systems under both amplitude and rate limited actuators. Since the input amplitude can be treated as a state of the actuator dynamics, in the presence of both amplitude and rate constraints, each closed-loop subsystem would be regarded as a partial state and input constrained system. Then, based on the linear differential inclusion method, we propose linear matrix inequality (LMI) conditions to design the decentralized state feedback controller that can handle the partial state and full rate constraints. Furthermore, we estimate the domain of attraction of both subsystems and the overall systems using the Cartesian product of the ellipsoidal sets. A numerical example is presented to demonstrate the validity of the proposed controller.

非線形最適制御によるPIOを防止する飛行制御系設計

In this paper, we propose a design method of a nonlinear optimal controller for systems with rate limited actuators which are known to cause PIO of an aircraft. The PIO prevention problem is solved as a robust stabilization problem of a servo system for pilot commands. Simulation results demonstrate that the nonlinear controller achieves faster tracking performance with less oscillation and smaller input compared with an anti-windup compensator using the H∞ method. Robustness against parameter error, observation noise and time-delay is also confirmed.

Absolute stability for the lateral-directional BWB model with rate limited actuator

In this paper the authors present a study regarding the interaction between the human pilot and the aircraft which may result in a dangerous phenomenon called Pilot Induced Oscillations (PIO), in the context of the lateral directional motion. The theoretical model of the airplane used is a Blended Wing Body (BWB) configuration and the human operator is expressed by the Synchronous Pilot Model (represented by a simple gain). The Popov criterion, in the case of the infinite parameter, is applied in order to investigate the absolute stability of the pilot-airplane linearized system in the presence of the rate saturation of the actuator.

A Survey of Force Feedback in Flight Safety Enhancement

This survey presents the application of force feedback in aviation. In modern fly-by-wire control system, actuator rate limit is the primary source of PIO II (Pilot Induced Oscillation II). The combination of smart-cue and smart-gain method can alleviate PIO II effectively, and consequently enhance the flight safety. The recent research of applying force feedback in aviation demonstrates that it is worthy of theoretical exploration and extensive utilization.

PIO I-II tendencies. Part 2. Improving the pilot modeling

The study is conceived in two parts and aims to get some contributions to the problem of PIO aircraft susceptibility analysis. Part I, previously published in this journal, highlighted the main steps of deriving a complex model of human pilot. The current Part II of the paper considers a proper procedure of the human pilot mathematical model synthesis in order to analyze PIO II type susceptibility of a VTOL-type aircraft, related to the presence of position and rate-limited actuator. The mathematical tools are those of semi global stability theory developed in recent works.

Schnelle Regelung linearer Systeme mit Stellgrößen- und Stellratenbegrenzungen

Zusammenfassung In diesem Artikel wird eine nichtlineare Zustandsrückführung für Regelstrecken mit linearer Dynamik unter Verwendung eines hinsichtlich Stellgröße und Stellrate beschränkten Stellgliedes vorgestellt. Dabei wird die Sättigung von Stellgröße und Stellrate zugelassen, wodurch sehr schnelle Regelvorgänge ermöglicht werden. Zur Bestimmung der Reglerparameter wird ein LMI-basiertes Entwurfsverfahren angegeben.

Anti-windup synthesis for systems with rate-limits using Riccati equations

This article develops an anti-windup (AW) scheme for systems with rate-limited actuators. The main results show how a full-order AW compensator can be synthesised using an algebraic Riccati equation and several free parameters. A further result then shows how the free parameters may be chosen to influence, in an intuitive way, the local gain of the system and the size of the region of attraction. The results are of interest due to their low computational burden and hence their applicability to the systems of large state dimension.

Existence, stability and robustness analysis of limit cycles in hybrid anti-lock braking systems

We investigate the stability and robustness properties of anti-lock braking systems (ABS) based on actuators with on/off dynamics. Namely, we propose a hybrid ABS controller which gives rise to an asymptotically stable limit cycle on the wheel slip. The proposed approach allows to derive exact information on the maximum allowable uncertainty in the measured variables which guarantee the cycle stability. Moreover, a structural stability analysis is performed with respect to different road conditions and to the actuator rate limit.

A comparison of rate-limit compensation schemes for pilot-induced-oscillation avoidance

It is known that rate-limited actuators may be responsible for causing Category II pilot-induced-oscillations (PIO's). This paper presents a comparison between two industry-develope rate limit compensators and an H ∞ compensator proposed in [C. Edwards, I. Postlethwaite, Anti-windup and bumpless transfer scheme, Automatica 24 (2) (1998) 199–210] and used in [M.C. Turner, D.J. Walker, A.G. Alford, Design and ground-based simulation of an H ∞ limited authority control system for the Westland Lynx helicopter, Aerospace Science and Technology 5 (2001) 221–234]. These are tested on an industry-standard aircraft model called ADMIRE, with nonlinear simulations. Overall, it is shown that the H ∞ compensator produces the best all-round performance for the input types considered, both in the pitch and the roll channels.

Limited Authority Adaptive Flight Control for Reusable Launch Vehicles

In the application of adaptive e ight control, signie cant issues arise due to limitations in the plant inputs, such as actuator displacement limits, actuator rate limits, linear input dynamics, and time delay. A method is introduced that allows an adaptive law to be designed for the system without theseinput characteristicsand then to be applied to the system with these characteristics, without affecting adaptation. This includes allowing correct adaptation while the plant input is saturated and allows the adaptation law to function when not actually in control of the plant. To apply the method, estimates of actuator positions must be found. However, the adaptation law can correct for errors in these estimates. Proof of boundedness of system signals is provided for a single hidden-layer perceptron neural network adaptive law. Simulation results utilizing the methods introduced for neural network adaptive control of a reusable launch vehicle are presented for nominal e ight and under failure cases that require considerable adaptation.

Hierarchical Approach to Adaptive Control for Improved Flight Safety

Following failures of primary aerodynamic actuators, safe flight can be maintained by introducing alternative actuation systems, such as analytically redundant secondary aerodynamic surfaces and propulsion, for higher-priority stability and control augmentation tasks. An intelligent hierarchical flight control system architecture is presented that is designed using nonlinear adaptive synthesis techniques and online learning neural networks to enhance flight safety. Pseudocontrol hedging is used for proper adaptation in the presence of actuator saturation, rate limits, and failure. The hierarchical structure incorporates nonactive secondary actuation channels that are engaged after a failure of a primary control surface is encountered. The methodology requires only the knowledge that a failure in a specific actuator has occurred. A model of the failed aircraft, the failure type, and the failure size need not to be known: The neural network element of the secondary channel will adapt to the failed actuator effect. The secondary control channels are designed to account for the typically lower authority and degraded performance that can be expected with secondary actuation systems. The proposed hierarchical flight control architecture is attractive, in particular, as a retrofit to existing certified flight control systems for enhanced flight safety. The proposed flight control architecture is evaluated in a nonlinear flight simulation environment, demonstrating its retrofit features.

Tailless aircraft flight control using multiple time scale reconfigurable sliding modes

A triple time scale tailless aircraft flight control problem is addressed via continuous sliding mode control. A reconfigurable sliding mode flight controller is designed that achieves robust, high accuracy command angle tracking both before and after damage to an aircraft. Command angles and angular rate commands are robustly tracked in outer and inner loops correspondingly via finite reaching time continuous sliding mode controllers. An optimal control allocation algorithm is employed using nominal mathematical model of an aircraft. Sliding surface boundary layer reconfiguration (direct adaptation) is used in the "very" inner loop to account for actuator dynamics, deflection limits, and rate limits. Online damage identification is not required by this design. The reconfigurable sliding mode flight control technique is applied to a flight dynamics model of a tailless jet fighter that was developed under is the innovative control effectors program. Simulations demonstrate stability and high accuracy tracking performance without violation of actuator limits.