Magnetic Field Control Device and Magnetic Field Control Method of Synchronous Machine

The present invention provides a magnetic field control device and a magnetic field control method for a synchronous machine, which can fundamentally cope with the problem of the lack and fluctuation in the voltage maintaining ability from a point of view of a power generation of a power system. A magnetic field control device of the present invention is a device for a synchronous machine that controls a magnetic field of the synchronous machine connected to a power system. The magnetic field control device comprises a magnetic field control system operating electric current flowing through a magnetic field coil of the synchronous machine; a regulator of the magnetic field control system; and a compensation circuit variably regulating a control constant of the magnetic field control system according to a magnitude of magnetic field current or an equivalent of the magnetic field current.