Patent ID: 7701090

Claim:
An active filter connected between a power system and a load to supply compensation current used to restrain a harmonic component in load current, comprising: voltage and current detecting means for detecting instantaneous voltage and instantaneous current at the power system; A/D converting means for converting the detected instantaneous voltage and the detected instantaneous current into digital data; active power instantaneous value and reactive power instantaneous value calculating means for calculating an active power instantaneous value and a reactive power instantaneous value using the instantaneous voltage and the instantaneous current converted to the digital data; active power effective value and reactive power effective value calculating means for calculating an active power effective value and a reactive power effective value using the calculated active power instantaneous value and the calculated reactive power instantaneous value by integration method; system side fundamental wave current calculating means for calculating fundamental wave current on the power system side using the calculated active power effective value and the calculated reactive power effective value; and compensation current output means for outputting the difference between the load current and the system side fundamental wave current as the compensation current.