Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

A direct digital control algorithm for low power reactors is proposed using logarithmic power level as input. The logarithmic power levels allow the use of fixed point arithmic resulting in faster calculation speeds than are obtainable with algorithms using floating point arithmetic. A stability analysis for various sampled data hold types is shown to have a 25% safety margin. A time optimal control sequence for power increases is derived using switch points. The switch points are determined using simulation techniques, eliminating the use of complex and approximate calculations. A practical demand level controller is developed using machine language programming to minimize the delay from the sampling of the neutron power to the output of control action. The controller is tested with digital and analog simulations of a thermal reactor showing that a successful, near time-optimal, control algorithm with general applications to low power reactors has been developed. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The ultimate measure of performance of any communication system is the subjective quality of the received message. In this thesis, the subjective quality of the output of a differential pulse code modulation (DPCM) system was measured as a function of the number of bits of quantization L, the speech bandwidth W, the ratio r of the sampling frequency fs to the Nyquist frequency 2W, and the number of feedback samples N. For previous-sample feedback (N = 1) the maximum subjective quality was obtained as a function of the bit rate R = 2rWL. The optimum sampling rate .was found to be the Nyquist rate; the improvement afforded by increasing fs over 2W was more than offset by the required increase in bit rate. Noise in the feedback loop caused by dc offset errors and noise present in the output of the feedback coefficient amplifiers prevented a thorough investigation of two- and three- sample feedback, although some results were obtained. The subjective quality of delta modulated (ΔM) speech was obtained vs r and W, and the quality of amplitude modulated (ΔM) speech was measured as a function of W and channel signal-to-noise ratio. A technique was then devised to use the AM results to estimate the subjective quality of phase modulated (PM) speech. A comparison was then made of the capabilities of PCM, DPCM, AM, single sideband-AM (SSB-AM), double sideband-AM (DSB-AM), and PM. It was found that when the available channel capacity is small, SSB-AM and DSB-AM are subjectively better than PCM', DPCM, and ΔM. However, for high quality speech communication, DPCM requires less channel capacity than PCM, ΔM, DSB-AM, SSB-AM or PM. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The object of this thesis is to build an interface between a computor and a three phase thyristor bridge rectifier, enabling the computor to control its D.C. output voltage. By writing a suitable computor program, this system was extended to provide closed loop computor control of the speed of a D.C. machine. The first interface and computor program were so designed that the computer provided the required analogue triggering delay for voltage control of the D.C. output. This setup did not allow for infinite variation of the voltage and occupied a large portion of the computor time. Thus it was decided to modify the interface, letting it provide its own delay, thus freeing the computor of the delay routine and giving it more time to do other tasks. Control of the bridge rectifier was also improved. When closed loop control was implemented, the system was found to be unstable. It was thus simulated and stabilized on the analogue computor. A new digital computor program was written incorporating those characteristics which were found necessary in the simulation to make the system stable. The modified form of compensation was found to give a satisfactory performance for both step and ramp inputs to the system as well as load transients on the D.C. motor. Various types of tachogenerator were tested to find which was the most suitable for operation with the computer. All the types tested gave satisfactory performances. The major factor affecting performance was the quality of the tachogenerator.

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