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 Adjustable frequency drive as a packaged low
harmonic drive solution.
M
M
M
130BB717.10
The active shunt filter monitors all three phase line
currents and processes 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 overcurrent of the input diodes.
Control
Manual
Disconnect
Fuse
Option
Soft charge
circuit
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0B
B7
19
.1
0
The factory settings allow for fast start-up, though
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. In this operation
mode the filter will also balance out the load to reduce
uneven load distribution between the three phases. The
steady state performance will allow the compensation of
harmonics until the 40th order, though the ultra-quick
current injection allows the filter to also compensate flicker
and other quick and short-term phenomenon. In selective
mode, the filter allows the user to program acceptable
individual harmonic levels between the 5th and 25th
orders. In selective mode the filter will not reduce even
harmonic orders or triplings, nor will it support phase load
balancing and flicker reduction.
In addition to the harmonic compensation mode the filter
also allows the user to program the filter priority from
either reactive current or harmonic compensation. If
harmonic compensation is chosen as the first priority, the
filter will use the necessary current for harmonic reduction
and energy for reactive current correction, though only if
Introduction to VLT Active ...
VLT Active Filter AAF 00x
MG.90.V2.22 - VLT
®
is a registered Danfoss trademark
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