Fault-Tolerant Control of Flexible Satellite with Magnetic Actuation and Reaction Wheel

Hajkarim, Mohammad Hossein | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51764 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Assadian, Nima
  7. Abstract:
  8. The primary goal of this thesis is to develop a Fault Tolerant Control (FTC) system for a flexible satellite in presence of actuators fault and failure. The actuators of the satellite are including three magnetorquers and three reaction wheels on each principal axis. At first, the three-degree-of-freedom rotational motion of a rigid satellite with two flexible solar panels is modeled. The flexible panels are modeled through the assumed mode approach by a finite set of bending modal motion. The ordinary differential equations of their generalized coordinates are found using the Lagrange’s equation. Then, the dynamic model is validated by comparing the simulation results of the model to the NX Siemens modelling software results. The satellite attitude is estimated using the FOAM method with the Sun and magnetometer sensors data. The body angular velocities are also estimated by a Kalman filter. It is supposed that the unknown fault or failure could occur just in actuators and the attitude sensors measurement have only a bounded noise. The results of the simulations show that many conventional controllers can be used for stabilizing and tracking a command in nominal situations. Nevertheless, when a fault or failure in one or more actuator occurs, these controllers fail to accomplish their mission. To achieve rest-to-rest attitude maneuvers by the combination of reaction wheels and magnetorquers in faulty situations, two different control laws of Passive Integral Sliding mode and Active Sliding mode are proposed. These control methods are robust against system’s uncertainties like the panels’ flexibility or unknown disturbances. The proposed FTCs are employed with both online and offline Control Allocation (CA) approaches. The advantage of the offline approaches is that they do not depend on the fault detection and identification algorithm. However, on the other hand, they are conservative with undesirable performance. The active sliding mode approach is coupled with an online control allocation system, which estimates the effectiveness of each actuator (fault coefficient). Although the proposed active sliding mode controller is more complicated, it has better performance than passive FTCs. In addition, the mentioned controllers are able to de-saturate the reaction wheels by using the magnetic torquer bars in presence of uncertainties, fault, and failure
  9. Keywords:
  10. Attitude Control ; Damage ; Refraction ; Magnetic Torquer Actuator ; Fault-tolerant Control ; Flexible Satellites ; Redundancy ; Reaction Wheel (RW)

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