Browsing by Author "Balas, Gary J."

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Anytime Control Algorithm: Model Reduction Approach
(American Institute of Aeronautics and Astronautics, 2004) Bhattacharya, Raktim; Balas, Gary J.
Recently, there has been considerable interest in anytime algorithms for real-time systems. Anytime algorithms are computational models that compromise quality of result for computational time. The tolerance to fluctuating CPU time makes anytime algorithms operationally optimal for real-time task scheduling. A methodology is presented that transforms linear control algorithms into anytime control algorithms. Implementation of a linear control algorithm involves matrix–vector multiplications that require a fixed computational time. Such algorithms fail to compute the controller output if the alloted CPU time is less than required and cannot make use of any excess CPU time that might be available. When implemented as a real-time system, the static nature of the required computational time makes it operationally suboptimal for task scheduling. Linear control algorithms are transformed to anytime control algorithms by switching between controllers of different order. Balanced truncation and residualization are considered as model reduction tools to generate a set of reduced-order controllers, and a switching algorithm is presented that smoothly switches between them to accommodate variation in available computational time.
Application of Parameter-Dependent Robust Control Synthesis to Turbofan Engines
(American Institute of Aeronautics and Astronautics, 1999) Wolodkin, Gregory; Balas, Gary J.; Garrard, William L.
Recent results in multivariable robust control synthesis for linear parameter-varying (LPV) systems are applied to the control of a turbofan engine over a wide range of power codes. Seven linear, time-invariant models are used in the control design. The resulting LPV controller consists of seven linear controllers, gain scheduled via linear interpolation. This gain-scheduled controller is obtained directly as part of the described design process, as opposed to conventional processes, where the gain schedules are developed after the fact to connect point designs. A model matching approach is employed such that the resulting closed loop resembles a decoupled set of second-order systems with specified rise times and overshoots. The performance of linear H point designs are compared with the LPV controller at fixed operating points. A nonlinear simulation is performed with the turbofan engine and LPV controller schedules as a function of the power code. The LPV controller exhibits excellent tracking of reference commands as the power code varies in time.
Blending Methodology of Linear Parameter Varying Control Synthesis of F16 Aircraft System
(American Institute of Aeronautics and Astronautics, 2002) Shin, Jong-Yeob; Balas, Gary J.; Kaya, M. Alpay
The design of a linear parameter varying (LPV) controller for the F-16 longitudinal axes over the entire flight envelope, using a blending methodology that lets an LPV controller preserve regional optimal solutions over each parameter subset and reduces computational costs for synthesizing an LPV controller, is presented. Three blending LPV controller synthesis methodologies are applied to control F-16 longitudinal axes. By the use of a function substitution method, a quasi-LPV model of the F-16 longitudinal axes is constructed from the nonlinear equations of motion over the entire flight envelope, including nontrim regions, to facilitate synthesis of LPV controllers for the F-16 aircraft. The nonlinear simulations of the blended LPV controller show that the desired performance and robustness objectives are achieved across all altitude variations.
Comparing Linear Parameter-Varying Gain-Scheduled Control Techniques for Active Flutter Suppression
(American Institute of Aeronautics and Astronautics, 2000) Barker, Jeffrey M.; Balas, Gary J.
Two linear parameter-varying gain-scheduled controllers for active flutter suppression of the NASA Langley Research Center’s Benchmark Active Control Technology (BACT) wing section are presented and compared to a previously presented gain-scheduled controller. The BACT wing section changes significantly as a function of Mach and dynamic pressure. The two linear parameter-varying (LPV) gain-scheduled controllers incorporate these changes as well as bounds on the rate of change of Mach and dynamic pressure. The inclusion of rate bounds in the design process allows for improved performance over a larger range of operating conditions than previously achieved by a linear fractional transformation gain-scheduled controller. The LPV controllers differ in that one primarily reduces coupling between the trailing-edge flap and the pitch and plunge modes, whereas the second optimizes wind gust attenuation. Closed-loop stability and improved performance are demonstrated via time simulations in which both Mach and dynamic pressure are allowed to vary in the presence of a Dryden wind-gust disturbance.
A Comparison between Hankel Norms and Induced System Norms
(Institute of Electrical and Electronic Engineers, 1998-11) Lu, Wayne W.; Balas, Gary J.
A general definition is formulated for the Hankel norms as the induced norms of a strictly proper stable linear time-invariant (LTIV) system mapping vector-valued Lp-past inputs to vector-valued Lq-future outputs. Some Hankel norms are derived by the maximum principle and duality. A property termed the system integral invariance is introduced by the derivation of those Hankel norms. Furthermore, the norm-induced initial conditions and the comparison between the Hankel norms and the induced system norms are also presented.
Comparison of μ- and H2-Synthesis Controllers on an Experimental Typical Section
(American Institute of Aeronautics and Astronautics, 1999) Vipperman, Jeffrey S.; Barker, Jeffrey M.; Clark, Robert L.; Balas, Gary J.
An experimental comparison of H2 - and μ-synthesized flutter suppression control systems was performed. A simple parametric uncertainty can be used to track changes in system dynamics as a function of dynamic pressure. The control system was implemented experimentally on a NACA 0012 test model of a typical section mounted in a low-speed wind tunnel. The pitching angle, flap angle, and plunge deflection of the airfoil were measured with sensors and fed back through the control compensator to generate a single control signal commanding the trailing-edge flap of the airfoil. The model of the aeroelastic system, including the dynamics of the sensors and actuators in the bandwidth of interest, was obtained using system identification techniques. For comparison purposes, an H2 control system with standard linear quadratic Gaussian weightings also was designed and implemented. When compared to the H2 control system, the μ-synthesis controller provided better disturbance rejection in the bandwidth of the unsteady aeroelastic dynamics. In addition, the μ controller required less control energy than the H2 control system. The final advantage of μ-synthesis is the ability to design an aggressive μ control system that is stabilizing across the range of operating dynamic pressures.
Control of the F-14 Aircraft Lateral-Directional Axis during Powered Approach
(American Institute of Aeronautics and Astronautics, 1998) Balas, Gary J.; Packard, Andrew K.; Renfrow, Joseph; Mullaney, Chris; M'Closkey, Robert T.
The design of linear controllers for the F-14 aircraft lateral-directional axis during powered approach using the structured singular-value (μ) framework is presented. Controllers are designed for an angle of attack of 10.5 deg and an airspeed of 137 kn, the on-speed flight condition. Each controller is implemented in a simplified nonlinear simulation and the full-order Fortran nonlinear simulation of the F-14. Pilot-in-the-loop simulations are used to verify their performance in the crewed flight simulator at the U.S. Naval Air Warfare Center, Patuxent River, Maryland. The μ controllers out perform the current analog and newly developed digital lateral-directional powered approach flight control system in pilot-in-the-loop simulations.
Control with Disturbance Preview and Online Optimization
(Institute of Electrical and Electronic Engineers, 2004-02) Jarvis-Wloszek, Zachary; Philbrick, Douglas; Kaya, M. Alpay; Packard, Andrew; Balas, Gary J.
We present an intuitive and self-contained formulation of a stability preserving receding horizon control strategy for a system where limited preview information is available for the disturbances. The simplicity of the derivation is due to (and its benefits somewhat offset by) a set of stringent and highly structured assumptions. The formulation uses a suboptimal value function for terminal cost, and relies on optimization strategies that only require a trivial improvement property, allowing implementation as an “anytime” algorithm. The nature of this strategy’s performance is clarified with linear examples.
Decentralized Receding Horizon Control and Coordination of Autonomous Vehicle Formations
(Institute of Electrical and Electronics Engineers, Inc., 2008-01) Keviczky, Tamas; Borrelli, Francesco; Fregene, Kingsley; Godbole, Datta; Balas, Gary J.
This paper describes the application of a novel methodology for high-level control and coordination of autonomous vehicle teams and its demonstration on high-fidelity models of the organic air vehicle developed at Honeywell Laboratories. The scheme employs decentralized receding horizon controllers that reside on each vehicle to achieve coordination among team members. An appropriate graph structure describes the underlying communication topology between the vehicles. On each vehicle, information about neighbors is used to predict their behavior and plan conflict-free trajectories that maintain coordination and achieve team objectives. When feasibility of the decentralized control is lost, collision avoidance is ensured by invoking emergency maneuvers that are computed via invariant set theory.
Development of Linear-Parameter-Varying Models for Aircraft
(American Institute of Aeronautics and Astronautics, 2004) Marcos, Andres; Balas, Gary J.
This paper presents a comparative study of three linear-parameter-varying (LPV) modeling approaches and their application to the longitudinal motion of a Boeing 747 series 100/200. The three approaches used to obtain the quasi-LPV models are Jacobian linearization, state transformation, and function substitution. Development of linear parameter varying models are a key step in applying LPV control synthesis. The models are obtained for the up-and-away flight envelope of the Boeing 747-100/200. Comparisons of the three models in terms of their advantages, drawbacks, and modeling difficulty are presented. Open-loop time responses show the three quasi-LPV models matching the behavior of the nonlinear model when in the trim region. Differences between the models are more apparent as the response of the aircraft deviates from the nominal trim conditions.
Falut-Detection Design for Uninhabited Aerial Vehicles
(American Institute of Aeronautics and Astronautics, 2006) Rotstein, Hector P.; Ingvalson, Ryan; Keviczky, Tamas; Balas, Gary J.
Fault Detection (FD) plays a vital role in ensuring the safety of a flight-control system, especially that of an uninhabited aerial vehicle. An FD algorithm is designed to detect a situation in which a faulty condition has occurred in the system. The main theoretical contribution of this work is a new residual threshold function, which is input dependent and enhances the FD capabilities of highly uncertain systems. The combined FD algorithm and new threshold function were simulated in the laboratory, in a high-fidelity hardware-in-the-loop environment, and flight tested as part of the Defense Advanced Research Projects Agency (DARPA) Software Enabled Control (SEC) Program. The DARPA SEC program is a research initiative designed to provide flight-control engineers with a reusable interface for the implementation of flight-control algorithms and flight management software on embedded systems.
Gain-Scheduled Lateral Control of the F-14 Aircraft during Powered Approach Landing
(American Institute of Aeronautics and Astronautics, 2000) Fialho, Ian; Balas, Gary J.; Packard, Andrew K.; Renfrow, Joseph; Mullaney, Chris
The design of a linear fractional transformation gain-scheduled controller, scheduled on angle of attack, for the F-14 aircraft lateral-directional axis is presented. The controller is designed for the powered approach flight phase, during which the angle of attack and corresponding airspeed varies from 2 deg and 182 kn to 14 deg and 126 kn. A linear fractional model of the lateral dynamics is constructed based on four linearized models that correspond to 2, 6, 10.5, and 14 deg angle of attack. Using parameter-dependent functions, a controller is designed that depends in a linear fractional manner on angle of attack and delivers uniform handling quality over angle-of-attack variations that lie between 2–14 deg. The resulting controller performs well when implemented in a nonlinear simulation model of the F-14 aircraft.
Gain-Scheduled Linear Fractional Control for Active Flutter Suppression
(American Institute of Aeronautics and Astronautics, 1999) Barker, Jeffrey M.; Balas, Gary J.; Blue, Paul A.
A gain-scheduled controller for active flutter suppression of the NASA Langley Research Center’s Benchmark Active Controls Technology wing section is presented. The wing section changes significantly as a function of Mach and dynamic pressure and is modeled as a linear system whose parameters depend in a linear fractional manner on Mach and dynamic pressure. The resulting gain-scheduled controller also depends in a linear fractional manner on Mach and dynamic pressure. Stability of the closed-loop system over a wide range of Mach and dynamic pressure is demonstrated. Closed-loop stability is demonstrated via time simulations in which both Mach and dynamic pressure are allowed to vary in the presence of input disturbances. The linear fractional gain-scheduled controller and an optimized linear controller (designed for comparison) both achieve closed-loop stability, but the gain-scheduled controller outperforms the linear controller throughout the operating region.
Identification of Flexible Structures for Robust Control
(Institute of Electrical and Electronic Engineers, 1989-06) Balas, Gary J.; Doyle, John C.
This article documents our experience with modeling and identification of an experimental flexible structure for the purpose of control design, with the primary aim being to motivate some important research directions in this area. Initially, a multi-input/multi-output model of the structure is generated using the finite element method. This model is inadequate for control design, due to its large variation from the experimental data. Next, Chebyshev polynomials are employed to fit the data with single-input/multli-output (SIMO) transfer function models. Combining these SIMO models leads to a multi-input/multi-output (MIMO) model with more modes than the original finite element model. To find a physically motivated model, an ad hoc model reduction technique which uses a priori knowledge of the structure is developed. The ad hoc approach is compared with balanced realization model reduction to determine its benefits. Descriptions of the errors between the model and experimental data are formulated for robust control design. Plots of select transfer function models and experimental data are included.
Invariant Subspaces for LPV Systems and their Applications
(Institute of Electrical and Electronic Engineers, 2003-11) Balas, Gary J.; Bokor, Jozsef; Szabo, Zoltan
The aim of this note is to extend the notion of invariant subspaces known in the geometric control theory of the linear time invariant systems to the linear parameter-varying (LPV) systems by introducing the concept of parameter-varying invariant subspaces. For LPV systems affine in their parameters, algorithms are given to compute many parameter varying subspaces relevant in the solution of state feedback and observer design problems.
Linear Parameter-Varying Detection Filter Design fora Boeing 747-100/200 Aircraft
(American Institute of Aeronautics and Astronautics, 2005) Szaszi, Istvan; Marcos, Andres; Balas, Gary J.; Bokor, Jozsef
We present a fault detection and isolation (FDI) filter design using a linear parameter-varying (LPV) model of the longitudinal dynamics of a Boeing 747 series 100/200. The LPV FDI filter design is based on an extension of the fundamental problem of residual generation concepts elaborated for linear, time-invariant systems. Typically, the FDI filters are designed for open-loop models, and applied in closed loop. An application is shown of an LPV FDI filter for actuator failure detection and isolation in the closed-loop longitudinal LPV system to the full nonlinear Boeing 747 aircraft simulation, which represents the “true” system.
Longitudinal Motion Control of a High-Speed Supercavitation Vehicle
(Sage Publishing, 2006-06-15) Arndt, Roger E.A.; Balas, Gary J.; Bokor, Jozsef; Vanek, Balint
This article focuses on theoretical developments in modeling and control of High-Speed Supercavitating Vehicles (HSSV). A simplified model of longitudinal dynamics is developed for control, and a dynamic inversion based inner-loop control technique is proposed to handle the switched, time-delay dependent behavior of the vehicle. Two outer-loop control schemes are compared for guidance level tracking. Various aspects of disturbance characteristics and actuator dynamics are investigated and analyzed.
Nonlinear Receding Horizon Control of an F-16 Aircraft
(American Institute of Aeronautics and Astronautics, 2002) Bhattacharya, Raktim; Balas, Gary J.; Kaya, M. Alpay; Packard, Andy
The application of receding horizon control (RHC) with the linear, parameter varying (LPV) design methodology to a high-fidelity, nonlinear F-16 aircraft model is demonstrated. The highlights are 1) use of RHC to improve upon the performance of a LPV regulator; 2) discussion on details of implementation such as control space formulation, tuning of RHC parameters, computation time and numerical properties of the algorithms; and 3) simulated response of nonlinear RHC and LPV regulator.
Optical Flow: A Curve Evolution Approach
(Institute of Electrical and Electronic Engineers, 1996-04) Kumar, Arun; Tannenbaum, Allen; Balas, Gary J.
A novel approach for the computation of optical flow based on an L1 type minimization is presented. It is shown that the approach has inherent advantages since it does not smooth the flow-velocity across the edges and hence preserves edge information. A numerical approach based on computation of evolving curves is proposed for computing the optical flow field. Computations are carried out on a number of real image sequences in order to illustrate the theory as well as the numerical approach.
Optimally Scaled H Infinity Full Information Control Synthesis with Real Uncertainty
(American Institute of Aeronautics and Astronautics, 1996) Balas, Gary J.; Lind, Rick; Packard, Andy
An algorithm to synthesize optimal controllers for the scaled H Infinity full information problem with real and complex uncertainty is presented. The control problem is reduced to a linear matrix inequality, which can be solved via a finite dimensional convex optimization. This technique is compared with the optimal scaled H Infinity full information with only complex uncertainty and D-K iteration control design to synthesize controllers for a missile autopilot. Directly including real parametric uncertainty into the control design results in improved robust performance of the missile autopilot. The controller synthesized via D-K iteration achieves results similar to the optimal designs.

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Browsing by Author "Balas, Gary J."