Abstract: An excitation control device controls excitation of a synchronous machine so as to absorb the harmonic current of a specified order superposed onto the current flowing between an electric power system to the synchronous machine.A harmonic detector selectively passes a harmonic component of the order of 6n.+-.1 in the detection signal detected by a current transformer. A pass signal of the harmonic detector is. 3-phase/2-phase converted by a rotating coordinate circuit into components on the orthogonal 2 axes on the rotating coordinate system rotating at an angular frequency of a fundamental current of the electric power system. At this time, the pass signal is calculated as a 6n-order harmonic current represented by the components on the normal two axes. The obtained 6n-order harmonic current is retrieved through a 6n-order harmonic filter, amplified by a power amplifier, and provided as an excitation current for the synchronous machine.

Abstract: A synchronous machine effectively absorbs higher harmonics in an AC system to which the synchronous machine is linked. The synchronous machine includes a damper winding, disposed on each magnetic pole and constituting by itself an independent closed circuit; capacitors, each of which is connected in parallel with each of several damper winding divisions obtained by dividing the damper winding at predetermined winding turns; a DC reactor for blocking flowing-in of higher harmonics to a DC power supply for DC excitation; a series resonant circuit further including the damper winding and the capacitors; and a series resonant circuit including the field winding and capacitors. Resonant frequencies of both series resonant circuits are set at 6 nf (n: an integer, f: a fundamental frequency) so as to greatly reduce impedance of the damper winding and the field circuit seen from an armature of the synchronous machine, by which to extinguish or reduce higher harmonics (6n.+-.1)f of the AC system.