User Manual

6
The SED2 reduces input line harmonic
currents without using line reactors or
DC link chokes
The resulting SED2 line current is appro-
ximately equivalent to a standard VSD
equipped with additional AC line reactors
or a DC link choke. Rather than perfor-
ming vector control calculations, the
controller now uses powerful new cont-
rol technologies to compensate for the
effects of the higher ripple DC link vol-
tage to assure smooth and quiet opera-
tion of the fan or pump motor.
■
Conclusion
Test results have demonstrated the abi-
lity of the SED2 to significantly reduce
the lower order harmonic currents drawn
from the AC power system without the
need for additional components.
Harmonic performance is equal or better
than that of conventional VSDs equipped
with additional AC line reactors or DC
link chokes.
■ HarmonEE
HarmonEE is a program specifically
de signed to calculate the harmonic cur-
rents, total harmonic current distortion
and total harmonic voltage distortion.
The data is then used to compare the
results against various international gui-
delines and standards such as IEEE519.2
(USA), EA G5/4 (UK and Hong Kong),
EN 61000-2-2 (Europe) and IEC (AS/NZ)
61000-3-6 (used globally). HarmonEE
will also be able to show the difference
of the LHT performance of the SED2
compared to a traditional VSD.
Siemens has introduced the SED2, a
family of VSDs designed specifically for
the HVAC market. Typical applications for
this drive are fan and pumps with vari-
able torque load characteristics. The fact
that these applications are low dynamic
by nature means the overall topology of
the SED2 now provides a new method of
reducing the input line harmonic cur-
rents without the addition of extra com-
ponents. It is known as LHT (Low Harmo-
nic Technology). Industrial VSDs are
typically designed with a 160 % + over-
load characteristic whereas the SED2
only requires 110 % overload to satisfy
the dynamics of a fan or pump. This fact
allows operation with significantly redu-
ced values of DC link capacitors – typi-
cally 2 % of a conventional VSD. This
means that the level of the DC link vol-
tage of the SED2 is lower and has more
ripple content than a conventional VSD
and this in turn results in a longer con-
duction period for the diodes in the rec-
tifier section. The SED2 input line current
no longer has the high amplitude narrow
pulse of charging current seen with
other VSDs but rather a quasi 120º con-
duction period per diode.