A Method for Exploiting Redundancy to Accommodate Actuator Limits in Multivariable Systems

TITLE AND SUBTITLE:
A Method for Exploiting Redundancy to Accommodate Actuator Limits in Multivariable Systems

AUTHOR(S):
Jonathan Litt and Greg Roulette

REPORT DATE:
December 1995

FUNDING NUMBERS:
WU-505-62-0L
1L161102AH45

PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES):
NASA Lewis Research Center
Cleveland, Ohio 44135-3191
and
Vehicle Propulsion Directorate
U.S. Army Research Laboratory
Cleveland, Ohio 44135-3191

PERFORMING ORGANIZATION REPORT NUMBER:
E-9460

SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
Washington, D.C. 20546-0001
and
U.S. Army Research Laboratory
Adelphi, Maryland 20783-1145

REPORT TYPE AND DATES COVERED:
Technical Memorandum

SPONSORING/MONITORING AGENCY REPORT NUMBER:
NASA TM-106859
ARL-TR-906

SUPPLEMENTARY NOTES:
Prepared for the 19th Science Conference sponsored by the U.S. Army, Orlando, Florida, June 20-24, 1994. Jonathan Litt, Vehicle Propulsion Directorate, U.S. Army Research Laboratory, NASA Lewis Research Center; and Greg Roulette, Shaker Heights High School, Shaker Heights, Ohio and Summer High School Apprenticeship Research Program participant at Lewis Research Center. Responsible person, Jonathan Litt, organization code 2530, (216) 433-3748.

ABSTRACT:
This paper introduces a new method for accommodating actuator saturation in a multivariable system with actuator redundancy. Actuator saturation can cause significant deterioration in control system performance because unmet demand may result in sluggish transients and oscillations in response to setpoint changes. To help compensate for this problem, a technique has been developed which takes advantage of redundancy in multivariable systems to redistribute the unmet control demand over the remaining useful effectors. This method is not a redesign procedure, rather it modifies commands to the unlimited effectors to compensate for those which are limited, thereby exploiting the built-in redundancy. The original commands are modified by the increments due to unmet demand, but when a saturated effector comes off its limit, the incremental commands disappear and the original unmodified controller remains intact. This scheme provides a smooth transition between saturated and unsaturated modes as it divides up the unmet requirement over any available actuators. This way, if there is sufficiently redundant control authority, performance can be maintained.

SUBJECT TERMS:
Multivariable control; Integrator windup; Control systems

NUMBER OF PAGES:
23

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