240 Rockwell Automation Publication MOTION-RM003I-EN-P - February 2018
Bit Usage Status Condition Description
20 Optional/
BD
DC Bus Unload
This bit is set by a CIP Motion converter, or a CIP Motion drive
containing an integral converter, or a CIP Motion drive connected
to an external non-CIP converter, to indicate that the converter
cannot continue supplying DC Bus power to other drives on a
shared DC Bus. This is usually th
e result of a shutdown fault action
initiated by the drive or converter, or a shutdown request from
the controller. Thus, when the DC Bus Unload bit is set, the
Shutdown bit (bit 18) should also be set. When there is no AC
Contactor Enable output to drop the DC Bus, a method is needed
to unload the converter from all other drives sharing the DC Bus.
By monitoring the DC Bus Unload status bit, the control system
can propagate Bus Power Sharing exceptions to all drives on the
shared DC Bus that are configured for Shared AC/DC or Shared DC
operation. This Bus Power Sharing exception invokes the
configured Exception Action that, by default, disables the drive
power structure, thereby unloading the bus. The Bus Power
Sharing Fault on these drives is a persistent fault that cannot be
cleared as long as the DC Bus Unload bit is set on this originating
drive or converter. The control system will simply regenerate the
Bus Power Sharing Faults based on the DC Bus Unload status bit
still being set.
Note that only the originating drive or converter with the DC Bus
Unload condition can cause Bus Power Sharing Faults on other
shared drives. In other words, no device with a Bus Power Sharing
Fault can cause a Bus Power Sharing exception on other shared
drives by setting its DC Bus Unload bit. This qualification prevents
DC Bus recovery deadlock. To recover full DC Bus operation, the
originating drive with the DC Bus Unload condition must first be
reset through a Shutdown Reset Request. Once clear, the Bus
Power Sharing Faults on the shared drives can then be
successfully cleared by either a Fault Reset Request, or a
Shutdown Reset Request, allowing these drives to become
operational.
21 Optional/
BD
AC Power Loss
This bit is set when a CIP Motion converter, or a CIP Motion drive
containing an integral converter, or a CIP Motion drive connected
to an external non-CIP converter, has detected a loss of AC input
power. This bit is cleared when AC input power is determined to
be sufficient for converter operation.
When an AC Power Loss condition is detected by a converter
supplying power to other drives over a shared DC Bus, a method is
needed to generate a Converter AC Power Loss exception on any
drive whose power structure is enabled. To accomplish this, the
control system monitors the AC Power Loss status bits of
converters supplying DC Bus power and propagates AC Power
Loss status to all drives on the shared DC Bus, such as drives that
are configured for Shared AC/DC or Shared DC operation. Upon
notification of AC Power Loss, drives that have enabled power
structures will assert a Converter AC Power Loss exception and
invoke the programmed Axis Exception Action. Disabled drives
will not generate an exception action on AC Power Loss. Thus, no
drive faults will occur on removal of AC Power from a converter as
long as no drive power structures drawing power from that
converter are enabled.
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