Rockwell Automation Publication DRIVES-AT005D-EN-P - May 2022 51
Chapter 5 Paralleling Two PowerFlex 755TM Regenerative Bus Supplies
For recommended settings and instructions for modifying the position of the power jumpers see the following publications:
• PowerFlex 750-Series Products with TotalFORCE® Control installation instructions, publication 750-IN100
, or PowerFlex 755TM IP00 Open
Type Kits installation instructions, publication 750-IN101
.
• PowerFlex 750-Series AC Drive installation instructions, publication 750-IN001
.
• Kinetix 5700 Servo Drives user manual, publication 2198-UM002
.
Precharge Interlocking
For more information about DC bus precharging and inverter precharging circuit configurations, see Precharge on page 11.
• If a disconnect switch is used between the common DC bus and the inverter DC input, the inverter must have precharging capability. In
addition, an auxiliary contact on the disconnect switch that opens when the disconnect is open must be wired to an inverter digital input. The
corresponding digital input must be assigned to the 'Precharge' enable function.
- PowerFlex 750-Series - assign to parameter 0:189 [DI Precharge]. See the PowerFlex 750-Series AC Drives programming manual,
publication 750-PM001
, for more information.
- PowerFlex 755TM - assign to parameter 0:190 [DI Precharge]. See the PowerFlex Drives with TotalFORCE Control programming manual,
publication 750-PM100
, for more information.
This configuration provides the proper precharge interlocking, which guards against possible damage to the drive when reconnecting the drive to
an energized DC bus.
• The precharge status of the PowerFlex 755TM regenerative bus supply should be interlocked with the connected drives, such that the drives
are disabled (aren’t running) when the PowerFlex 755TM regenerative bus supply is in a precharge state. This interlocking can be
accomplished by monitoring bus supply line side converter parameter 13:225.25 [Line Side Sts 1]. This status bit can be connected to the
PowerFlex 'Enable' and Kinetix 5700 'Regeneration OK' control via:
- hardwired bus supply I/O connection to inverter/drive local I/O
- Logix controller I/O
- communication DataLink within the Logix control program task
Product may require optional I/O modules if hardwired interlocking methods are used.
Parallel Operation of Two PowerFlex 755TM Regenerative Bus Supplies
When bus supplies are paralleled, the two units must be powered by dedicated isolation transformers.
• One of the regenerative bus supply AC sources must be ungrounded to help prevent circulating common mode currents between the two
bus supplies.
• There are several acceptable methods for isolation of the two regenerative bus supplies:
- Dual secondary transformer with delta and wye secondary windings
- Two separate isolation transformers could also be used. Secondary windings can be either delta or wye
• One of the regenerative bus supply AC sources can be solid grounded (this diagram), high resistance grounded or ungrounded with zig-zag
transformer, neutral ground resistor (NGR), and ground indicator filter. See Chapter 2
for more information about regenerative bus AC source
grounding methods and recommendations.
• AC source and DC Bus bar configuration must be symmetrical when installing a parallel PowerFlex 755TM regenerative bus supply system.
• Parameter 13:45 [DC Bus Ref Sel] must be set to 2 'Droop Ctrl' on each of the PowerFlex 755TM regenerative bus supplies.
ATTENTION: The DC bus power jumpers for PowerFlex 755T bus supplies (PE-B),
all connected PowerFlex inverters (PE-B), and all Kinetix 5700 servo drives
(ground screw/jumper) must all be set to the same condition: all removed (out).
Risk of equipment damage exists if the DC bus power jumpers aren’t all set to the
same condition.
ATTENTION: The Kinetix family of drives and some PowerFlex AC drives
have no external means of controlling the precharge; therefore, a DC
disconnect switch must not be used without the use of an external
precharge device. See Precharge on page 11
.
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