Synchronous machine excitation control device for absorbing harmonics

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. Using the excitation current, a current having the same amplitude as, but opposite phase to, the harmonic current of the order of 6n.+-.1 flows as an armature current in the synchronous machine. Thus, the harmonic current of the specified order superposed onto the system current can be canceled.