FEASIBILITY STUDY OF USING A DIGITAL COMPUTER AS A VARIABLE-AMPLITUDE VARIABLE-FREQUENCY OSCILLATOR

Abstract

Previous studies have shown that a dual-excited synchronous generator (a machine which has two identical field windings on the rotor: one on the d-axis and the other on the q-axis) can run asynchronously at any speed and still generate voltage at constant frequency. This capability of the generator can be utilized for variable-speed constant-frequency operation if the windings are both excited by slip frequency alternating currents. The main problem in such schemes is the design of a source which can supply such control signals whose frequency changes with the slip. This thesis is a feasibility study of using a digital computer as a variable-amplitude variable-frequency oscillator; which generates the two-phase sinusoidal excitation control signals for the dual-excited synchronous gener­ator. In this thesis, the oscillator control methodology is formulated and ex­perimentally verified. The performance of the oscillator is experimentally investigated. The experimental results of the methodology verification and the oscillator performance tests are presented. The results show that it is feasible to use a digital computer as a variable-amplitude variable-frequency oscillator. The oscillator software-based design is flexible for generating different types of signal waveforms. By a single control variable, the software can be configured to vary the oscillator frequency range, and to greatly reduce (almost eliminate) the harmonic distortion of the output signals. Some recommendations for further research are included.