HARMONIC CURRENT DETECTING METHOD FOR ACTIVE FILTER

摘要

PURPOSE: To eliminate necessity for setting up a plurality of auxiliary CTs so that leveling at the detection of each load current can be performed, by obtaining a signal by filtering only a reference frequency component, from a synthesized signal of directly adding to each other a current transformation ratio-corrected current detection signal, to serve as a required harmonic current detection signal. CONSTITUTION: In a current/voltage converter circuits 31a,..., 31n, a both end voltage drop of a resistor is utilized, to perform current/voltage conversion, also to correct a voltage signal output in accordance with a current transformation ratio correcting coefficient set by correction coefficient setting circuits 32a,..., 32n. Each voltage signal is directly added on the output side of each converter circuit, to input a synthetic signal to a harmonic current detecting circuit 33. In the harmonic current detecting circuit 33, an addition signal of each reference frequency component is filtered to be subtracted from the synthetic signal, also to be multiplied by a suitable constant, and a required harmonic current detection signal is input to a control circuit 2. In this way, the required harmonic current detection signal is obtained by a voltage signal transformed from a secondary side detection current i1 to in of each CT.