US 5,498,994 AGranted

Active filter device

AssigneeMitsubishi Denki Kabushiki Kaisha

InventorMichihiro Furuta

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Abstract

An active filter device simple in construction and low in price in which higher harmonic components can be stably suppressed without requiring a passive filter even when a load to be compensated includes a capacitative load. Such an active filter device includes: a current transformer for detecting a load current; a frequency detection circuit for detecting higher harmonic components contained in the load current; a first three-phase/two-phase conversion circuit for determining a reference compensation current for compensating for the current with respect to a first frequency among the higher harmonic components; a first filter circuit; a first two-phase/three-phase conversion circuit; a first phase compensation circuit; an n-th three-phase/two-phase conversion circuit for determining a reference compensation current for compensating for the current with respect to an n-th frequency; an n-th filter circuit; an n-th two-phase/three-phase conversion circuit; an n-th phase compensation circuit; an adder for synthesizing the respective reference compensation currents with respect to the first frequency and the n-th frequency; an inverter circuit for outputting a resultant compensation current based on the output from the adder; and an inverter transformer.

Claims10

Dependent claims

An active filter device for filtering harmonic current components in a power line of a system including a power supply source coupled to a load, said active filter comprising:

a current detector coupled to said power line for detecting a load current
a frequency detection circuit coupled to said power line for detecting each of a first to an n-th frequency components contained in said load current so as to output them, wherein n is an integer greater than 1;
a first to an n-th reference compensation current processing circuits each of which performs the phase compensation for the corresponding frequency component detected by said current detector so as to determine a reference compensation current for corresponding frequency component, said first to n-th compensation current processing circuits being connected to said current detector and to said frequency detection circuit;
an adder for adding the output from each of said processing circuits so as to generate a resultant reference compensation current;
a control section connected to said adder for generating a control signal based on the output from said synthesizer;
an inverter circuit coupled to said control section driven by the control signal output from said control section;
and
an inverter transformer coupled between said power line and said inverter circuit for sending out to said system a compensation current for suppressing a higher harmonic contained in said load current on the basis of the output from said inverter circuit.

5 more elements

Dependencies are inferred from the claim text.