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Davison, E. J.

Publications and source records attributed to Davison, E. J..

11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

A Study on the Control of Third Generation Spacecraft

An overview of some studies which have recently been carried out on the control of third generation spcecraft, as modelled by the MSAT space vehicle configuration, is made. This spacecraft is highly nonsymmetrical and has appendages which cannot in general be assumed to be rigid. In particular, it is desired to design a controller for MSAT which stabilizes the system and satisfies certain attitude control, shape control, and possibly stationkeeping requirements; in addition, it is desired that the resultant controller should be robust and avoid any undesirable spill over effects. In addition, the controller obtained should have minimum complexity. The method of solution adopted to solve this class of problems is to formulate the problem as a robust servomechanism problem, and thence to obtain existence conditions and a controller characterization to solve the problem. The final controller obtained for MSAT has a distributed control configuration and appears to be quite satisfactory.

Davison, E. J.↗
NASA NTRS1981

Penetrating transmission zeros in the design of robust servomechanism systems

In the design of a robust servomechanism system, it is well known that the system cannot track a reference signal whose frequency coincides with the transmission zeros of the system. This paper proposes a new design method for overcoming this difficulty. The controller to be used employs a sampler and holding device with exponential decay. It is shown that the transmission zeros of the discretized system can be shifted by changing the rate of the exponential decay of the holding device. Thus, it is possible to design a robust controller for the discretized system to track any reference signal of given frequency, even if the given frequency coincides with the transmission zeros of the original continuous-time system.

Wang, S. H.↗
NASA NTRS1979

Design of flight control systems via robust decoupled servomechanism theory

Decoupling theory and robust servomechanism theory are applied to the design of linear multivariable systems with large parameter variations. In addition to being approximately decoupled in the transient period, the over-all system achieves tracking and disturbance rejection robustly in the steady state. An example in flight control system is given.

Wang, S.-H.↗
NASA NTRS1978

An algorithm for obtaining the minimal realization of a linear time-invariant system and determining if a system is stabilizable-detectable

A definition of centralized fixed modes of a system, which is an adoption of the definition of fixed modes for a decentralized system is made. It is shown that the centralized fixed modes of a system can be easily and efficiently calculated in terms of the eigenvalues of the system, and that the calculation of such fixed modes enables one to determine, in a numerically efficient way, whether a system is controllable, observable, stabilizable, or detectable. An efficient algorithm for reducing a system to minimal realization form is then given. The algorithms have been effectively used on systems of order up to 100.

Davison, E. J.↗
NASA NTRS1978

Minimization of transmission cost in decentralized control systems

This paper considers the problem of stabilizing a linear time-invariant multivariable system by using local feedback controllers and some limited information exchange among local stations. The problem of achieving a given degree of stability with minimum transmission cost is solved.

Wang, S.-H.↗
NASA NTRS1978

Observing partial states for systems with unmeasurable disturbances

This paper considers the problem of observing a set of linear functionals of states for systems with unmeasurable disturbances. A transfer function approach is adopted to characterize the set of observers for a given system. The result also has direct application to state estimation in decentralized control systems.

Wang, S.-H.↗
NASA NTRS1975

Observing the states of systems with unmeasurable disturbances

In order to estimate the state of a linear time-invariant multivariable system by using a Luenberger observer, it is generally assumed that all system inputs are measurable. This correspondence presents a simple and useful procedure for the construction of minimal-order state estimators for systems with unmeasurable disturbances.

Wang, S.-H.↗
NASA NTRS1975

On the computation of minimal indices for linear multivariable systems

This paper presents an algorithm for the computation of the minimal indices for linear multivariable systems. The same algorithm can be used to determine the rank of a transfer function. As an application, this algorithm is shown to be useful in the design of non-interacting control systems.

Wang, S. H.↗
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.↗