ABB ACS850 - Harmonic Distortion; Regenerative Power

27
•
ave,mot
aven,recave,recave,rec
)i(ave,rec
)i(ave,mot
I
)P...PP(
P
.I ×
+++
×=
21
201
•
,maxmot
n,maxrec,maxrec,maxrec
)i,max(rec
)i,max(mot
I
)P...PP(
P
.I ×
+++
×=
21
201
Where:
• I
mot,ave(i)
and I
mot,max(i)
are the AC input currents of the concerned AC input
• P
rec,ave(i)
and P
rec,max(i)
are the power ratings of the drive module connected to the
concerned AC input
• P
rec,ave1
… P
rec,aven
and P
rec,max1
… P
rec,maxn
are the power ratings of the drive modules
connected to the AC input
• the factor 1.20 covers the load unbalance due to the variation of the characteristics
of the individual choke(s) and drive module(s) from the nominal ones
• I
mot,ave
and I
mot,max
are calculated from P
mot,ave
and P
mot,max
as in the single AC input
case.
Harmonic distortion
If there are requirements for harmonic distortion level, a mains choke (CHK-xx) is
typically needed in ACS850 frames A and B. Other drive types have a choke as
standard.
Total harmonic distortion is about 40…45%, when a choke is used according to default
selection. Then also the requirements for harmonic distortion according to standards
IEC 61000-3-2, IEC 610003-4, and IEC 610003-12 are typically fulfilled.
A more accurate harmonics analysis can be made with the sizing tool DriveSize. See
also ABB’s Guide to Harmonics with AC Drives in AC Drives Technical Guide Book for
basic theory about this topic.
Regenerative power
Regenerative power is fed by the motor to the DC link when the motor produces
negative torque and then brakes. This is typical when the motor is decelerating or
when the motor is in a so called generator mode (for example, unwinder). If the other
drive modules do not take enough active power from the DC link at the same time, the
braking energy is stored in the DC link capacitors and the DC link voltage increases. A
low amount of regenerative energy can be handled within the common DC capacitors if
the DC link voltage stays below the trip limit.
The regenerative energy should be removed from the system if the energy capacity of
the common DC system is not enough. This can be done by braking resistors or by
feeding the excess energy back to the supply network. Either resistor braking or an
external regenerative supply unit can be used.
Common DC configurations