ABB ACS850 series, Application Manual

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29
The available energy capacity now depends on the criteria for the
U
dc,lim
and the actual
DC link voltage supplied into the common DC system. The selection of the value for
U
dc,lim
depends on the common DC system configuration and its general requirements.
Here are the common alternatives for the
U
dc,lim
based on the drive module DC voltage
limits (see also section DC voltage limits ):
•
the absolute maximum limit is defined according to the DC overvoltage trip limit
including some safety margin
•
840
≤
V DC
,lim dc
U
•
DC over voltage control is enabled, but not activated
810
≤
V DC
lim , dc
U
•
DC link voltage level where the braking choppers are not yet activated
780
≤
V DC
,lim dc
U
To determine whether the energy capacity is adequate (that is, the selected
U
dc,lim
voltage level is not reached), the following condition must be fulfilled:
•
W
dc
> E
gen
Where
E
gen
is the regenerative energy to the DC link during the generating period:
•
dt P E
gen gen
∫
=
Resistor braking
The braking chopper is either included as standard in the drive modules or it is a built-
in option, depending on the drive type. For a list, see
Chokes, braking choppers and
charging circuits . The external braking resistor can be connected to the drive module.
The braking chopper can then feed the braking energy to the resistor to keep the DC
link voltage below the trip limit.
M M M M
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~
~
~
~
~
~
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Common DC configurations