The promise and potential of controllers that can reconfigure themselves in the
case of control effector failures and uncertainties, and yet guarantee stability and
provide satisfactory performance, has led to fault tolerant control being an active
area of research. This thesis addresses this issue with the design of two fault tolerant
nonlinear Structured Adaptive Model Inversion control schemes for systems with fixed
magnitude discrete controls. Both methods can be used for proportional as well as
discrete controls. However, discrete controls constitute a different class of problems
than proportional controls as they can take only binary values, unlike proportional
controls which can take many values.
Two nonlinear control laws based on Structured Adaptive Model Inversion are
developed to tackle the problem of control failure in the presence of plant and operating
environment uncertainties. For the case of redundant actuators, these control
laws can provide a unique solution. Stability proofs for both methods are derived and
are presented in this thesis.
Fault Tolerant Structured Adaptive Model Inversion that has already been developed
for proportional controls is extended here to discrete controls using pulse width
modulation. A second approach developed in this thesis is Fault Tolerant Control
Allocation. Discrete control allocation coupled with adaptive control has not been
addressed in the literature to date, so Fault Tolerant Control Allocation for discrete
controls is integrated with SAMI to produce a system which not only handles discrete control failures, but also accounts for uncertainties in the plant and in the operating
environment.
Fault tolerant performance of both controllers is evaluated with non real-time
nonlinear simulation for a complete Mars entry trajectory tracking scenario, using
various combinations of control effector failures. If a fault is detected in the control
effectors, the fault tolerant control schemes reconfigure the controls and minimize the
impact of control failures or damage on trajectory tracking. The controller tracks
the desired trajectory from entry interface to parachute deployment, and has an
adaptation mechanism that reduces tracking errors in the presence of uncertainties in
environment properties such as atmospheric density, and in vehicle properties such as
aerodynamic coefficients and inertia. Results presented in the thesis demonstrate that
both control schemes are capable of tracking pre-defined trajectories in the presence of
control failures, and uncertainties in system and operating environment parameters,
but with different levels of control effort.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-3092 |
| Date | 15 May 2009 |
| Creators | Marwaha, Monika |
| Contributors | Valasek, John |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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