Patent ID: 7787267

Claim:
An active power filter, comprising: an energy storage capacitor providing a regulated DC voltage; an inverter including a plurality of power electronic switches, with the inverter electrically connecting with two terminals of the energy storage capacitor for switching the regulated DC voltage; a filtering circuit providing two sets of terminals with one of the two sets electrically connecting to the inverter and another of the two sets electrically connecting to power lines between a power source and a load; and a controller outputting control signals transmitted to the inverter for driving the power electronic switches; wherein the controller detects a source current, a source voltage and an energy storage capacitor voltage for calculating a reference signal and detects an output current tracking the reference signal through a feedback control of the controller, so as to control the power electronic switches of the inverter generating a compensating current; wherein the controller further comprises a harmonic current loop having a first current sensor, a band-rejection filter and a harmonic calculating and amplifying circuit, with the first current sensor detecting the source current and transmitting a signal through the band-rejection filter to filter out the signal of a fundamental component, the harmonic calculating and amplifying circuit receiving an output of the band-rejection filter to calculate the harmonic component of each specified order and then amplifying the harmonic component of each specified order by different gains to form a part of the reference signal; wherein the compensating current comprises the harmonic components of specific assigned orders to attenuate a compound of the harmonic currents of specific orders with a predetermined attenuating ratio.