Abstract
The ever-increasing use of artificial satellites in both the study of terrestrial and space phenomena demands a search for increasingly accurate and reliable pointing systems. It is common nowadays to employ reaction wheels for attitude control that provide wide range of torque magnitude, high reliability, and little power consumption. However, the bearing friction causes the response of wheel to be nonlinear, which may compromise the stability and precision of the control system as a whole. This work presents a characterization of a typical reaction wheel of 0.65 Nms maximum angular momentum storage, in order to estimate their friction parameters. It used a friction model that takes into account the Coulomb friction, viscous friction, and static friction, according to the Stribeck formulation. The parameters were estimated by means of a nonlinear batch least squares procedure, from data raised experimentally. The results have shown wide agreement with the experimental data and were also close to a deterministic model, previously obtained for this wheel. This model was then employed in a Dynamic Model Compensator (DMC) control, which successfully reduced the attitude steady state error of an instrumented one-axis air-bearing table.
Highlights
This paper presents a Dynamic Model Compensator (DMC) control of reaction wheel in current control mode
The torque applied to the wheel is sensed by the satellite in the opposite direction, allowing the attitude control based on information of inertial sensors like gyroscopes, sun sensors, magnetometers and star sensors
In speed mode a secondary outer control loop regulates the current to eliminate the error between the commanded angular speed and the flywheel speed, which is measured by some sort of rate sensor
Summary
This paper presents a Dynamic Model Compensator (DMC) control of reaction wheel in current control mode. The controller used command in current with dynamic compensation based only on Coulomb and viscous frictions With this method it was possible to reduce the error during wheel rotation inversion by an order of magnitude. For the estimation of parameters by means of a least squares procedure, the state to solve for is composed by the angular velocity, the motor constant, viscous friction coefficient, Coulomb torque and static torque. This is an indication that these experiments are able to provide information for this and other estimation parameters, which will be presented
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