Circutor AFQm Series, Instruction Manual

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38
AFQm
Instruction Manual
4�1�3�- HARMONIC COMPENSATION
Active filters are devices responsible for the compensation of harmonic currents.
Compensation is achieved by injecting harmonic currents equal to those in the installation in
counter phase.
This means that upstream of the filter connection point, the signal shows virtually no harmonic
distortion (
Figure 31
).
L1
L2
L3
S1 S2
P1
P2
S1
S2
P1 P2
CARGAS / LOADS
RED / MAIN
N
S1 S2
P1
P2
I
F
I
C
I
R
AFQm
Figure 31: General connection diagram of an active filter.
4.2.- OPERATING PRINCIPLE
Active filters are based on the following principle:
I
FILTER
= I
MAINS
- I
LOAD
Equation 4:Operating principle�
In other words, they detect the difference between the desired sine wave ( I
M
ainS
) of the current
and the signal deformed by the harmonics ( I
LOAD
). And they inject the difference between both
waves ( I
FILTER
).
Figure 32
shows the wave shapes of the currents injected by the active filters.
These show the required wave ( I
M
ainS
), the existing deformed wave ( I
LOAD
) and the filter current
( I
FILTER
).