flow direction. This means that the returned energy from the
motor and mechanical systems that are decelerated, is
passed on to the mains as regenerated electrical energy. A
passive diode rectifier front end would require a braking
resistor to consume the surplus energy as heat. In
applications with frequent decelerations an AFE is thus more
energy efficient. Also the practical aspects with removing the
heat from a braking resistor is eliminated.
The LCL filter reduces the ripple current of the switching
frequency and its harmonics into the mains. A damping
resistor Rd is connected in series with the filter capacitor Cf
to stabilize the filter resonance.
The three standard power units operate in parallel to achieve
the required power levels. The standard power units in the
AFE are identical to the power units in the frequency
converters. One AFE centralized controller regulates and
controls the three parallel power units.
Transformer
460 V
AFE
560 kW
Master
560 kW
Slave
560 kW
Slave
Control signals
130BA771.10
L
m
L
t
C
f
L
C
R
d
Illustration 2.1 Active Front End Topology
Safety Instructions and Gen...
VLT
®
Active Front End AFE 302 Operating Instructions Liebherr
MG.33.X2.02 - VLT
®
is a registered Danfoss trademark 7
2 2
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