Excitation control device

An excitation controller controls excitation of a synchronous machine, which is connected to a power transmission system through a transformer, so that a high-side voltage of the transformer is maintained at a target voltage with high accuracy. An output terminal target voltage of the synchronous machine is set to precisely compensate for a voltage drop in the transformer, corresponding to the transformer phase angle variation. To achieve this result, the excitation controller detects an output terminal voltage and an output current of the synchronous machine and calculates active and reactive currents of the output current, sets the output terminal target voltage of the synchronous machine from the active and reactive currents, the high-side voltage of the transformer, and the reactance of the transformer, and controls excitation of the synchronous machine to compensate for the voltage drop in the transformer corresponding to phase angle variation of the transformer.