3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Design of an adaptive dynamic inversion-based neurocontroller for a tandem-controlled agile surface-to-air missile(2019) Phahlamohlaka, K JConventional plant-model dependent controller design approaches such as gain scheduling work well for simple flight envelope and airframe geometry. For complex flight envelope and airframe the approach results in a costly exercise to obtain a high-fidelity plant model. In this study an adaptive controller design approach is taken for an agile dual aerodynamically controlled DAC missile autopilot. Adaptive controller approach does not require an exhaustive plant model and has the capability of accommodating plant uncertainty and unmodelled dynamics online. A direct model reference adaptive control MRAC is investigated with different adaptive rules for the DAC missile. A two time-scale separation dynamic inversion controller with proportional-integral controller was used as the baseline controller of the proposed MRAC controller. The two time-scale separation controller was benchmarked with a gain scheduled three loop autopilot. A radial basis function neural network RBFNN is used to approximate the unmatched uncertainty of the missile dynamics. Adaption of the uncertainties is done on the fast dynamics controller to ensure fast recovery. The uncertainty of the slow dynamics is handled with a proportional-integral PI controller. The following adaptive rules were used with the RBFNN adaptive loop recovery ALRItem An investigation of techniques for nonlinear state observation(2016) McBride, Dean Christian TaitAn investigation and analysis of a collection of different techniques, for estimating the states of nonlinear systems, was undertaken. It was found that most of the existing literature on the topic could be organized into several groups of nonlinear observer design techniques, of which each group follows a specific concept and slight variations thereof. From out of this investigation it was discovered that a variation of the adaptive observer could be successfully applied to numerous nonlinear systems, given only limited output information. This particular technique formed the foundation on which a design procedure was developed in order to asymptotically estimate the states of nonlinear systems of a certain form, using only partial state information available. Lyapunov stability theory was used to prove the validity of this technique, given that certain conditions and assumptions are satisfied. A heuristic procedure was then developed to get a linearized model of the error transient behaviour that could form the upper bounds of the transient times of the observer. The technique above, characterized by a design algorithm, was then applied to three well-known nonlinear systems; namely the Lorenz attractor, the Rössler attractor, and the Van Der Pol oscillator. The results, illustrated through numerical simulation, clearly indicate that the technique developed is successful, provided all assumptions and conditions are satisfied.