Title

H∞ Control for the PACOSS DTA *

Report Number

WL-TR-91-3078 Volume I, p. CAB-1 thru CAB-17

Creator

Vothtand, Christopher T.

Stoughton, R. Michael

Corporate Author

Research and Technology Department
Martin Marietta Civil Space Company

Laboratory

Wright Laboratory

Date

1991

Date Issued

1991-08

Extent

17

Contract

Laboratory Research - No Contract

DoD Project

2401

DoD Task

240104

Identifier

ADA241311

Format

1 online resource

Abstract

This paper presents an application of an H∞design technique to the active control of a passively damped large space structure test article. An active vibration
suppression compensator was designed for the Passive and Active Control of Space Structures (PACOSS) Dynamic Test Article (DTA) using the H∞ technique. Analytic studies indicate passive damping of the structure results in reduced sensitivity to variations in plant structural modes for a given level of performance.
The control problem was to reduce the X and Y Line-of-Sight (LOS) pointing errors caused by deformation of the structure due to vibration. External disturbances at four locations along the DTA excite the vibrational modes of the structure, resulting in LOS errors. Passive damping elements designed into the structure result in open-loop damping ratios ranging from 0.12 to 0.02. Active suppression of structural modes is accomplished using 10 proof-mass actuators located on the structure. Sensors for active control provide 20 colocated inertial and relative velocity measurements as well as 3 noncolocated inertial velocity measurements at locations along the structure. The H∞ approach allowed the integration of performance requirements, robustness requirements, and other design constraints into the design problem. Explicit representation of model uncertainties was important in achieving a closed-loop system insensitive to plant variations typical of flight hardware. Implementation of the resulting controller on the DTA structure provided experimental verification of closed-loop system stability and performance in the presence
of model errors typical of test verified structures possessing high modal density. An investigation of the relationship between the active control and passive damping indicated that passive damping was instrumental in achieving performance and reduced sensitivity to structural mode uncertainty. Passive damping of the structure also aided in reduction of the controller order for hardware implementation.

Description

This paper presents an application of an H∞design technique to the active control of a passively damped large space structure test article. An active vibration
suppression compensator was designed for the Passive and Active Control of Space Structures (PACOSS) Dynamic Test Article (DTA) using the H∞ technique. Analytic studies indicate passive damping of the structure results in reduced sensitivity to variations in plant structural modes for a given level of performance.
The control problem was to reduce the X and Y Line-of-Sight (LOS) pointing errors caused by deformation of the structure due to vibration. External disturbances at four locations along the DTA excite the vibrational modes of the structure, resulting in LOS errors. Passive damping elements designed into the structure result in open-loop damping ratios ranging from 0.12 to 0.02. Active suppression of structural modes is accomplished using 10 proof-mass actuators located on the structure. Sensors for active control provide 20 colocated inertial and relative velocity measurements as well as 3 noncolocated inertial velocity measurements at locations along the structure. The H∞ approach allowed the integration of performance requirements, robustness requirements, and other design constraints into the design problem. Explicit representation of model uncertainties was important in achieving a closed-loop system insensitive to plant variations typical of flight hardware. Implementation of the resulting controller on the DTA structure provided experimental verification of closed-loop system stability and performance in the presence
of model errors typical of test verified structures possessing high modal density. An investigation of the relationship between the active control and passive damping indicated that passive damping was instrumental in achieving performance and reduced sensitivity to structural mode uncertainty. Passive damping of the structure also aided in reduction of the controller order for hardware implementation.

Distribution Classification

1

Distribution Conflict

No

DTIC Record Exists

No

Illinois Tech Related

No

Photo Quality

Not Needed

Report Availability

Full text available

Type

article

Is Part Of

Proceedings of Damping '91: 13-15 February 1991 San Diego, California (Pages AAC-1 through DCC-19)