Characteristics of Variable Speed Brushless Self-Excited Type Synchronous Generator System

This paper presents a variable speed synchronous generator system. The system consists of a brushless self-excited type synchronous generator and a bi-directinal voltage source PWM frequency changer. The rotor field windings of the generator are short-circuited with diodes, and the field excitation is obtained through the half-wave rectification of the induced voltages. To induce the AC voltages in the field windings which are rotating at synchronous speed, the stator output currents of the generator are so controlled by the PWM converter coupled to the generator that they can contain DC components. In addition, the rotating fields which are produced by harmonic components included in the stator current, are used effectively to obtain a self-excitation. The system can provide power generation into the power system over a wide speed range at unity power factor.In this paper, a simulation of the steady state characteristics of the generator is given, which takes account of both the resistance of each winding and the interruption of the rotor field current caused by the insertion of the diode, also the characteristics of the system are clarified through both the simulation and experiments.