The promise and potential of controllers that can reconfigure themselves in thecase of control effector failures and uncertainties, and yet guarantee stability andprovide satisfactory performance, has led to fault tolerant control being an activearea of research. This thesis addresses this issue with the design of two fault tolerantnonlinear Structured Adaptive Model Inversion control schemes for systems with fixedmagnitude discrete controls. Both methods can be used for proportional as well asdiscrete controls. However, discrete controls constitute a different class of problemsthan proportional controls as they can take only binary values, unlike proportionalcontrols which can take many values.Two nonlinear control laws based on Structured Adaptive Model Inversion aredeveloped to tackle the problem of control failure in the presence of plant and operatingenvironment uncertainties. For the case of redundant actuators, these controllaws can provide a unique solution. Stability proofs for both methods are derived andare presented in this thesis.Fault Tolerant Structured Adaptive Model Inversion that has already been developedfor proportional controls is extended here to discrete controls using pulse widthmodulation. A second approach developed in this thesis is Fault Tolerant ControlAllocation. Discrete control allocation coupled with adaptive control has not beenaddressed in the literature to date, so Fault Tolerant Control Allocation for discretecontrols 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 operatingenvironment.Fault tolerant performance of both controllers is evaluated with non real-timenonlinear simulation for a complete Mars entry trajectory tracking scenario, usingvarious combinations of control effector failures. If a fault is detected in the controleffectors, the fault tolerant control schemes reconfigure the controls and minimize theimpact of control failures or damage on trajectory tracking. The controller tracksthe desired trajectory from entry interface to parachute deployment, and has anadaptation mechanism that reduces tracking errors in the presence of uncertainties inenvironment properties such as atmospheric density, and in vehicle properties such asaerodynamic coefficients and inertia. Results presented in the thesis demonstrate thatboth control schemes are capable of tracking pre-defined trajectories in the presence ofcontrol failures, and uncertainties in system and operating environment parameters,but with different levels of control effort.
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