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Results for “feedback linearization”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

The generalized pole assignment problem

For some linear, strictly proper system given by its transfer function, two dynamic output feedback problems can be posed. The first one is that of using dynamic-output feedback to assign the closed-loop characteristic polynomial and the second that of assigning the closed-loop invariant factors. These problems and their interrelationships are discussed. The formulation is done in the frequency domain and the investigation carried out from an algebraic point of view, in terms of linear equations over rings of polynomials. Using the notion of genericity, several necessary and sufficient conditions are expressed.

Djaferis, T. E.↗
NASA NTRS1973

The state space and transfer function approaches in practical linear multivariable systems design.

A procedure using transfer function formalism for stabilizing a multivariable feedback system with significant plant uncertainty is presented. The method shapes nominal loop functions and decreases their magnitudes with frequency in such a manner that the system remains stable throughout the plant uncertainty range. An example illustrates the application of the described procedure.

Shaked, U.↗
NASA NTRS1978

Linear modelling of attentional resource allocation

Eight subjects time-shared performance of two compensatory tracking tasks under conditions when both were of constant difficulty, and when the control order of one task (designated primary) was varied over time within a trial. On line performance feedback was presented on half of the trials. The data are interpreted in terms of a linear model of the operator's attention allocation system, and suggest that this allocation is strongly suboptimal. Furthermore, the limitations in reallocating attentional resources between tasks, in response to difficulty fluctuations were not reduced by augmented performance feedback. Some characteristics of the allocation system are described, and reasons for its limitations suggested.

Pierce, B.↗
NASA NTRS1990

Exact Linearization For Control Of Robots

Equivalence of several theoretical approaches discussed. Report comments on application of geometric control theory (GCT), resolved-acceleration control (RAC), operational-space control (OSC), and nonlinear-decoupling theory (NDT) to remote manipulator consisting of multiple rigid links. Principal concern, search for nonlinear feedback law making end effector behave, for purposes of control, as though its dynamics linear and decoupled.

Kreutz, Kenneth K.↗
DOE OSTI2021

The Phase-Locking of Tropical North Atlantic and the Contribution of ENSO

The Tropical North Atlantic (TNA) is characterized by significant interannual variability in sea surface temperature (SST), which is phase-locked to the boreal spring. In this study, the phase-locking of TNA is investigated by adopting a linear stochastic-dynamical model (SDM) using seasonally modulated TNA feedbacks together with the seasonal modulation of ENSO forcing. In the observations, the role of local TNA feedbacks and ENSO forcing in TNA phase-locking are equivalently important with both preferring the peak of TNA variability to appear in the boreal spring. Besides, the seasonal modulation of TNA feedbacks and ENSO forcing strength are both mainly controlled by thermodynamic processes. In most climate models, the contribution of ENSO on TNA phase-locking is weaker than that in observations. The strength of ENSO-related TNA phase-locking is highly correlated with the relationship between ENSO and TNA, which is mainly determined by the amplitude of ENSO and its teleconnection patterns.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

DERMS Online: A New Voltage Sensitivity-Enabled Feedback Optimization Framework

This paper proposes a distributed energy resource management system (DERMS) solution by developing a new voltage sensitivity-enabled feedback optimization framework. The key idea is to adopt a measurement feedback scheme to reformulate the original nonlinear optimization into a linear programming (LP) problem via perturb-and-observe-based voltage sensitivity analysis. The proposed solution eliminates the dependence on load knowledge and can be implemented online thanks to an efficient open-source solver for LP problems. Comparison results with other control methods on a real distribution feeder in Southern California highlight the feasibility as well as benefits for the proposed framework.

distributed energy resource management↗
NASA NTRS1964

Linear digital control.

Linear discrete of digital controller design for optimal regulation of feedback control systems

OPTIMAL CONTROL↗
NASA NTRS1970

Minimax control of a system with process uncertainty in substate space

The control of a single input-single output plant with parameter uncertainty was approached using a minimax technique. A linear time invariant controller results which requires only partial state feedback and is optimal in the sense that it minimizes a quadratic criterion involving tracking error, control, and parameter uncertainty. Bounded input-bounded output stability is guaranteed provided the transfer function has only left half plane zeros. If uncertainties are bounded, it is always possible to stabilize the system when sufficient control amplitude is available. The number of states required to generate the control is equal to the system order less the number of zeros.

Basuthakur, S.↗
NASA NTRS1973

On the stabilization of decentralized control systems.

This paper considers the problem of stabilizing a linear time-variant multivariable system by using several local feedback control laws. Each local feedback control law depends only on partial system outputs. A necessary and sufficient condition for the existence of local control laws with dynamic compensation to stabilize a given system is derived. This condition is stated in terms of a new notion, called fixed modes, which is a natural generalization of the well-known concept of uncontrollable modes and unobservable modes that occur in centralized control system problems. A procedure that constructs a set of stabilizing feedback control laws is given.

Wang, S.-H.↗
NASA NTRS1976

Space shuttle pogo active controller design using frequency domain optimization

A frequency domain parameter optimization technique was used to design active pogo suppression controls for the space shuttle. The technique uses a conjugate gradient search procedure and is well suited for designing low-order controllers for higher order systems. The shuttle model was a two-pump and six-structural-mode linear model representing a worst-case condition. A promising feedback controller structure was found to be a lead-lag design.

Seidel, R. C.↗
NASA NTRS1976

On the optimal minimum order observer-based compensator and the limited state variable feedback controller

Four design problems are considered: two on the optimal minimum order observer-based compensator design and two on the optimal limited state variable feedback controller. The problem of designing an optimal discrete time linear time-invariant observer-based compensator for the regulation of an n dimensional linear discrete time time-invariant plant with m independent outputs is considered. This is a stochastic design problem to the extent that the initial plant state is assumed to be a random vector with known first and second order statistics. The compensator parameters are obtained by minimizing the expectation, with respect to the initial conditions, of the standard cost, quadratic in the state and control vectors with the inclusion of cross terms.

Llorens-Ortiz, B.↗
NASA NTRS1978

Approach guidance logic for a tilt-rotor aircraft

The distinctive feature of a tilt-rotor aircraft is that the pilot can change the rotor mast angles to go from a helicopter configuration for take-off and landing to an airplane configuration for high cruise speeds and vice-versa. An approach path for such an aircraft is proposed and the logic required to fly along this path in the presence of wind is determined. The main contribution of this work is an efficient and, to my knowledge, new method for generating the nominal state and control histories taking into account an estimate of the mean wind velocity and direction. The method requires the solution of algebraic (mostly linear) equations to generate a 'universal nominal', and feedforward and feedback gains. Then, in flight the additional state and control corrections due to deviation in descent rate, deceleration, and flight in a steady wind are obtained by multiplying simple precalculated functions of time by descent rate, deceleration or sine and cosine components of the mean wind vector. Simulations of approach flights for different wind conditions, assuming perfect state information in the feedback signal, indicated satisfactory performance.

Beser, J.↗
NASA NTRS1984

High sensitivity laser interferometry for detection of boundary-layer transition

A high sensitivity laser interferometry for continuous monitoring of optical path changes is presented. The sensitivity to small changes in the optical path is achieved by means of a feedback system which keeps the interferometer at its maximum (and linear) position. Two experiments were designed to verify the interferometer's performance, both in direct and in scattering configurations. In each case, small temperature fluctuations were introduced as the signal source. Simultaneous measurement of temperature were compared with the results of the interferometer. Good correlation between the results were obtained. Finally, the application of the high sensitivity interferometer for detection of boundary-layer transition is examined. Optical signal strength and possible sources of noise are examined. Some methods of model surface preparation for enhancement of signal-to-noise ratio are discussed.

Modarress, D.↗
NASA NTRS1985

The Kronecker indices of affine-nonlinear control systems

The Kronecker indices of smooth affine-nonlinear control systems presently defined are noted to determine the collection of controllable linear systems that are obtainable on the basis of local feedback equivalences and state-space reductions. Because attention is given to the invariants of systems under equivalences, and the behavior of these invariants under mappings that arise from state submersions, local representations of systems are used wherever possible to render cases more accessible.

Lewis, J. H.↗
NASA NTRS1986

Robust multivariable controller design for flexible spacecraft

Large, flexible spacecraft are typically characterized by a large number of significant elastic modes with very small inherent damping, low, closely spaced natural frequencies, and the lack of accurate knowledge of the structural parameters. Summarized here is some recent research on the design of robust controllers for such spacecraft, which will maintain stability, and possible performance, despite these problems. Two types of controllers are considered, the first being the linear-quadratic-Gaussian-(LQG)-type. The second type utilizes output feedback using collocated sensors and actuators. The problem of designing robust LQG-type controllers using the frequency domain loop transfer recovery (LTR) method is considered, and the method is applied to a large antenna model. Analytical results regarding the regions of stability for LQG-type controllers in the presence of actuator nonlinearities are also presented. The results obtained for the large antenna indicate that the LQG/LTR method is a promising approach for control system design for flexible spacecraft. For the second type of controllers (collocated controllers), it is proved that the stability is maintained in the presence of certain commonly encountered nonlinearities and first-order actuator dynamics. These results indicate that collocated controllers are good candidates for robust control in situations where model errors are large.

Joshi, Suresh M.↗
NASA NTRS1987

Direct adaptive control of manipulators in Cartesian space

A new adaptive-control scheme for direct control of manipulator end effector to achieve trajectory tracking in Cartesian space is developed in this article. The control structure is obtained from linear multivariable theory and is composed of simple feedforward and feedback controllers and an auxiliary input. The direct adaptation laws are derived from model reference adaptive control theory and are not based on parameter estimation of the robot model. The utilization of adaptive feedforward control and the inclusion of auxiliary input are novel features of the present scheme and result in improved dynamic performance over existing adaptive control schemes. The adaptive controller does not require the complex mathematical model of the robot dynamics or any knowledge of the robot parameters or the payload, and is computationally fast for on-line implementation with high sampling rates. The control scheme is applied to a two-link manipulator for illustration.

Seraji, H.↗