A new variable-speed AC generator system using a brushless self-excited-type synchronous machine

A new variable-speed synchronous generator system is proposed. The system consists of a brushless self-excited-type synchronous machine and a voltage source PWM frequency changer. In the generator, the field current is obtained by superimposing another field on the stator rotating field, which is achieved by control of the PWM converter so that AC voltages are induced and half-rectified in the rotor field windings. Neither an exciter nor additional exciting equipment is required for this generator. In order to superimpose the additional field on the stator field, two modulation schemes of the PWM converter of the frequency changer are given and the characteristics of this generation system are discussed on simulation and experimental results