What you post is true, but is not an answer to the original question. The OP has now told us that this is a full sized alternator of 2.7megawatts, not a baby one in a car for a kilowatt or so, and the rectifiers are rotating, to avoid the need for exciter slip rings and brushes.
Varying the Vdc allows the magnet strength to be adjusted to separate the functions of voltage control and rotation rate.
A noddy diagram to illustrate what is under discussion is reproduced below, the main generation occurs in the stator not show around the armature of the mains machine.
The attraction is that there are no high current paths that involve moving contacts, so no brushes to wear etc.
What you post is true, but is not an answer to the original question. The OP has now told us that this is a full sized alternator of 2.7megawatts, not a baby one in a car for a kilowatt or so, and the rectifiers are rotating, to avoid the need for exciter slip rings and brushes.
Varying the Vdc allows the magnet strength to be adjusted to separate the functions of voltage control and rotation rate.
A noddy diagram to illustrate what is under discussion is reproduced below, the main generation occurs in the stator not show around the armature of the mains machine.
The attraction is that there are no high current paths that involve moving contacts, so no brushes to wear etc.
