| 摘要 |
PROBLEM TO BE SOLVED: To provide a signal-detecting circuit which can extract fundamental wave components or higher harmonics components of a current waveform, following a fluctuation or change in an AC frequency, and also provide an active filter device which can surely compensate for higher harmonic current of an AC power system, even if there is fluctuation or change in the AC frequency. SOLUTION: A load current waveform of a power system line 1 is detected by a load current detector 2, and the detected value is input to a switch capacitor filter (SCF) 3. Then a voltage waveform of the power system line 1 is detected by a phase voltage detector 4, and a switching signal having a frequency a specified times as large as that of the voltage waveform is output from a phase-locked loop circuit into the SCF 3. Then, the SCF 3 extracts the fundamental wave components included in the load current and then higher harmonic components are output from a subtractor 10. An inverter section 20 is controlled such that a higher harmonic wave controlled waveform IH output from a compensation current detecting section 25 and a compensation current waveform IC detected by a current detector 18 are squal. |
