A New Self-Excitation Scheme for Three-Phase Synchronous Generators.

Abstract

For three-phase synchronous generators, a new self-excitation scheme has been developed. The generator employed this scheme behaves as a flat-compound machine without any automatic voltage regulators. The stator of the generator is provided with an armature winding which generates the fundamental and 2nd-harmonic mmfs. The rotor is equipped with a field winding and a harmonic winding. The harmonic winding is magnetically coupled to the 2nd-harmonic mmf produced by the armature winding. Making the current flow in the stator armature winding by way of a three-phase set of capacitors connected across its three-phase terminals, the ac voltage is induced in the rotor harmonic winding due to the armature 2nd-harmonic mmf. By connecting the harmonic winding to the fled winding through a rectifier circuit, self-excitation of the generator is obtained. This excitation scheme is both self-excited and brushless, and no exciter is required. Additionally, the voltage regulation due to the load variation can be improved by connecting the capacitors of suitable value.In this paper the operating principle and circuit configuration of the generator are explained, and the experimental results using a 1kVA prototype machine are shown. Then, the generator characteristics are theoretically clarified by approximate analysis, and appropriateness of the theory and the usefulness of the proposed scheme are experimentally confirmed.