3 Introduction to VLT Active Filter AAF00x
3.1.1 Working Principle
VLT
®
Active Filter AAF00x is a device for harmonic current
mitigation and reactive current compensation. The unit is
designed for installation in various systems and
applications as centrally installed filter(s) or combined with
a VLT frequency converter as a packaged low harmonic
drive solution.
M
M
M
130BB717.10
The active shunt filter monitor all three phase line currents
and process the measured current signal via a digital
signal processor system. The filter then compensates by
actively imposing signals in counter phase to the
unwanted elements of the current.
130BB718.10
The counter phase signals are generated by setting
different IGBT switches in real time feeding a DC-voltage
into the grid. The compensated current waveform is
smoothened via a built-in LCL filter making sure that the
IGBT switching frequency and DC-component is not
imposed to the grid. The filter is able to operate on
generator or transformer supply and is able to reduce
individual motor, non-linear loads or mixed loads. All
nonlinear-loads (diode feed loads) must hold AC coils to
protect these units against over current of the input
diodes.
Control
Manual
Disconnect
Fuse
Option
Soft charge
circuit
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0B
B7
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.1
0
The factory settings allow for fast start-up but dedicated
programming is possible through the local user control
panel LCP allowing adaptation to more demanding
applications.
The filter allows either overall or selective harmonic
compensation modes. In overall compensation mode all
harmonics will be reduced towards zero. The filter will in
this operation mode also balance out the load to reduce
uneven load distribution between the three phases. The
steady state performance will allow compensate of
harmonics until 40th order but the ultra-quick current
injection allow the filter also to compensate flicker and
other quick and short term phenomenon. In selective
mode the filter allows the user to program acceptable
individual harmonic levels between 5th and 25th order.
The filter will in selective mode not reduce even harmonic
orders nor triplings and will not support phase load
balancing and flicker reduction.
Beside the harmonic compensation mode the filter also
allow the user to program the filter priority from either
reactive current or harmonic compensation. If harmonic
compensation is chosen as the 1st priority, the filter will
use needed current for harmonic reduction and use energy
for reactive current correction only if excessive energy is at
hand. The filter will automatically and continuously assign
energy between 1st and 2nd priority to provide highest
Introduction to VLT Active ...
VLT Active Filter AAF 00x
MG.90.V2.02 - VLT® is a registered Danfoss trademark
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