No description available.

No description available.

A thesis submitted to the Faculty of Engineering and the Built Environment in fulfilment of the requirement for the degree Doctor of Philosophy, University of the Witwatersrand, Johannesburg, 2019 / The design of feedback stabilizing controllers is an essential component of control engineering theory and practice. A large part of the modern literature in control theory is devoted to coming up with new methods of designing feedback stabilizing controllers. This sustained interest in answering the question \how to design a feedback stabilizing controller" has not been accompanied by equal interest in the more existential and fundamental problem of \when is a system stabilizable by feedback". As such the theory of control Lyapunov functions still remains the most general framework that characterizes stabilizability as a system property. This approach however simply replaces one elusive and di cult concept (i.e stabilizability) with an equally diffcult concept, the existence of control Lyapunov functions. In this thesis we analyse control system stabilizability from the perspective of control system quotients which are generalized control system reductions, the focus being on the propagation of the stabilizability property from the lower order quotient system to the original system. For the case where the quotient system is a linear controllable system we prove that propagation of the stabilizability property to the original system is possible if the zero dynamics of the original system are stable. A novel way of constructing the zero dynamics which does not involve the solution of a system of partial differential equations is devised. More generally for analytic non-linear systems given a stabilizable quotient system, we develop a new method of constructing a control Lyapunov function for the original system, this construction involves the solution of a system of partial di erential equations. By studying the integrability conditions of this associated system of partial differential equations we are able to characterize obstructions to our proposed method of constructing control Lyapunov functions in terms of the structure of the original control system. / PH2020

published_or_final_version / Electrical Engineering / Master / Master of Science in Engineering

No description available.

No description available.

No description available.

No description available.

Reliable controller designs have been developed in this thesis for a number of finite-horizon and infinite-horizon problems with possibly non-zero initial conditions. These reliable controllers assure that system stability and system performance will be maintained despite certain system faults. The performance measure used in this thesis is an "H[subscript ���]-like norm", which is an induced two-norm from all exogenous signals and initial conditions to the regulated output and final states. Controller designs and existence conditions are presented for a reliable controller for faults in any pre-selected subset of actuators or sensors. Also, controller designs and an existence condition are presented for a reliable controller for any single sensor or actuator fault using sensor and actuator redundancy. / Graduation date: 1999

Increasing densities on magnetic data storage devices leads to problems of severe intersymbol interference (ISI), additive noise and non-linearities. Advanced detection strategies for magnetic recording channels fall into two categories: partial response equalization with maximum likelihood decoding and decision feedback equalization. This study focuses on doing an adaptive all-pass forward filter for the decision feedback channel. The decision feedback channel can be equalized by a low-order continuous-time filter, and does not require a transversal filter with high-precision multiplication. This results in considerable savings in both power consumption and chip die area. One problem that has yet to be addressed is how to adaptively set the coefficients of the all-pass filter. This thesis examines the design and performance of an adaptive all-pass filter. The performances in terms of the mean-squared error (MSE) of a first- and second-order all-pass are evaluated. They are compared to a conventional FIR filter design of various lengths. An adaptive algorithm based on the least mean-squared (LMS) error is developed and characterized over a range of storage densities. Since this does not require sampling of the filter input or any states of the forward filter, the system could be realized in continuous-time up to the decision device. Numerical simulations for various data densities and noise variances are done to verify the theoretically expected performance and the adaptation behavior of the all-pass. / Graduation date: 1997