H∞ Control for the PACOSS DTA *
Report Number: WL-TR-91-3078 Volume I, p. CAB-1 thru CAB-17
Author(s): Vothtand, Christopher T., Stoughton, R. Michael
Corporate Author(s): Research and Technology Department Martin Marietta Civil Space Company
Laboratory: Wright Laboratory
Date of Publication: 1991-08
Pages: 17
Contract: Laboratory Research - No Contract
DoD Project: 2401
DoD Task: 240104
Identifier: This paper is part of a conference proceedings. See ADA241311
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.
Author(s): Vothtand, Christopher T., Stoughton, R. Michael
Corporate Author(s): Research and Technology Department Martin Marietta Civil Space Company
Laboratory: Wright Laboratory
Date of Publication: 1991-08
Pages: 17
Contract: Laboratory Research - No Contract
DoD Project: 2401
DoD Task: 240104
Identifier: This paper is part of a conference proceedings. See ADA241311
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.