A new brushless excitation method for 4-pole three-phase synchronous generator with cylindrical-rotor

For a 4-pole three-phase synchronous generator with cylindrical-rotor, a new brushless excitation method is proposed. The stator of the generator is provided with a 4-pole three-phase main winding and a 6-pole single-phase exciting winding. The generator has a nonsalient-pole rotor. The field winding is a distributed winding placed in slots and arranged so as to produce an approximately sinusoidal 4-pole field. When the 6-pole stator exciting winding is excited by DC current, the AC voltage is induced in each rotor field coil. The rotor field coils are connected with diodes, respectively, so as to make the same 4-pole magnetic field as the stator main winding. The each field coil consists of a half-wave rectification circuit. The rotor field excitation is controlled proportionally by the stator DC exciting current. By this scheme a brushless 4-pole three-phase synchronous generator without exciter has been achieved. In the paper the operating principle and the circuit configuration of the generator are described in detail, and experimental results using a 2 kVA prototype machine are shown