MICROCOMPUTER-BASED REAL-TIME TWO-PHASE EXCITATION SYSTEM FORA VARIABLE-SPEED DUAL-EXCITED SYNCHRONOUS GENERATOR
Yonah, Zaipuna Obedi
Recent studies have demonstrated that a dual-excited synchronous generator (DESG) can be applied as a variable-speed constant-frequency (VSCF) generating system. In such an application, this machine, which has two excitation windings, requires two-phase slip frequency excitation voltages. Thus, the practical application of this DESG for VSCF operation depends on the ability to generate and control these two-phase excitation voltages. In this thesis, the problem of developing an excitation system for a variable-speed DESG is investigated as a signal generation problem. The problem is to generate a two-phase excitation supply which satisfies, in real time; the excitation requirements of the variablespeed DESG. The proposed solution to tins excitation problem has a frequency regulation (FR) scheme and a voltage regulation (VR) scheme. Based on these regulation schemes, a computer-based, real-time, two-phase excitation system for a variable-speed DESG has been developed, implemented and tested. The excitation system uses a novel and flexible signal generation scheme to meet the excitation requirements of tile variable-speed DESG. The development, the implementation, and the testing of tile excitation system are described in the thesis, The implemented FR and VR schemes control tile two excitation voltages simultaneously, but act independently. Experimental results showing the real-time performance of tile excitation system and the response of a laboratory DESG driven at variable speeds are presented. These results show that the excitation system is flexible, fast acting, and accurate. The excitation system is flexible in that, the amplitude, the frequency, the frequency-range, and the phase sequence of the two generated excitation voltages can all be controlled dynamically (on-line). In addition, the waveform distortion of the excitation voltage signals can be specified on-line and, once specified, this distortion is independent of the frequency of the generated signals. With the FR and VR schemes both acting automatically, the DESG can supply power at any desired frequency and terminal voltage while its rotor is driven at a variable speed.