50 Rockwell Automation Publication DRIVES-AT005D-EN-P - May 2022
Chapter 5 Paralleling Two PowerFlex 755TM Regenerative Bus Supplies
Figure 13 - PowerFlex 755TM Regenerative Bus Supply with Parallel PowerFlex 755TM Regenerative Bus Supply
Compatibility Table
See Table 1 on page 19.
General Considerations
• All system components must be selected for the same AC-line voltage.
• A low inductance type DC bus must be used. See DC Bus Connections on page 10
for details.
• The common DC bus system may require feeder and branch circuit protection and disconnect devices. Provide appropriate circuit
protection as required by national and local electrical safety codes and regulations.
• Depending on product family and frame size, AC and/or DC fuses may be provided internally or must be supplied external to the product.
See Appendix A
and the product technical data manuals for recommended fuse information.
• PowerFlex 755T AC drives and bus supplies must not be used on undersized or high-impedance AC supply systems. The supply system kVA
must be equal to or greater than the product-related kW, and the system impedance must be less than 10%. Operation outside these limits
can cause instability and product shutdown. You must account for the kVA of all PowerFlex 755T drives and bus supplies on the distribution
system and the system impedance of upstream transformers.
- System Impedance = (PowerFlex 755T kVA ÷ Transformer kVA) x Transformer % Impedance
• Wiring of inverters connected to the DC bus must go to a common point on the DC bus bars to make sure that the system is symmetrical
between the two PowerFlex 755TM regenerative bus supplies.
• The mixture of different frame size drives in this arrangement can cause high ripple current in the smaller frame drives. In this case, place
the larger power drives physically closer to the bus supply. This helps current sharing among the various drives on the bus
• The AC input power jumpers (PE-A) must be placed in the correct positions according to the power source grounding method. The PowerFlex
755T regenerative bus supply and all connected inverters must have the DC bus jumpers (PE-B) removed or set to 'out' regardless of the AC
power source grounding method. The Kinetix 5700 servo drives must have the ground screw/jumpers removed. The PowerFlex 755T
regenerative bus supply is an active converter.
+DC
-DC
L1
L2
L3
PE
+DC
-DC
L1
L2
L3
PE
• AC and DC circuit protection devices are required but not
shown. See Appendix A
for more information.
• The bus supplies must be sized to power all inverters
connected to the DC bus. See Sizing Regenerative Bus
Supply on page 23 for more information.
• Additional DC bus capacitance may be required. See DC
Bus Capacitance Calculation Method on page 87 for more
information.
• Additional DC bus conditioner units may be required. See
Table 1 on page 19
.
• Inverter units aren’t shown in this diagram. See Table 1 on
page 19 for more information.
• Several methods are acceptable for isolation of the two
regenerative bus supplies. This diagram shows a 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) or high resistance grounded.
High-resistance grounded power sources require a ground
fault indicator filter. See Appendix B
for more information.
• Delta secondary power sources require a Zig-Zag
Transformer and ground fault resistor (GFR) to convert the
ungrounded power system to resistance grounded. See
Appendix B
for more information.
•See Chapter 2
for more information about regenerative bus
AC source grounding methods and recommendations.
• One of the regenerative bus supply AC sources must be
ungrounded to help prevent circulating common mode
currents between the two converters.
3-Phase
AC Supply
Isolation
Transformer
Bus Supply Converter
Precharge
PowerFlex 755TM
Regenerative Bus Supply
PowerFlex 755TM
Regenerative Bus Supply
Bus Supply Converter
Precharge
Bus
Cond
Bus
Cond
Cap
Bank
DC
Bus
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