Rockwell Automation 20Y PowerFlex Active Front End - Manual (Page 154)

154 Rockwell Automation Publication 20Y-UM001E-EN-P - July 2014
Appendix C Application Notes
Paralleling AFEs The power of the AFE input group can be increased by connecting several groups
in parallel. Paralleling refers to AFE units connected on the same input
transformer and the same DC bus. No communication between the units is
required—they work independently.
Paralleling is typically used when the power range of a single frame size is not
enough, or when redundancy is needed. For additional information, see Drives in
Common Bus Configurations, publication DRIVES-AT002.
Guidelines for AFEs in IP20 2500 MCC Style Enclosure
• For AFEs in IP20 2500 MCC Style enclosures, a maximum of two AFEs
of the same power size (for example, two Frame 10 AFEs) and same voltage
class can be paralleled.
• Each AFE must have its own LCL filter.
• Each AFE must have its own short-circuit protection on AC and DC
sides. See
Appendix A for fusing information. When paralleling, you must
check the sufficient short-circuit capacity of the system.
• The AFE units must be derated by 5% of their power rating.
• Configure the following parameters for parallel operation:
–
Set Parameter 42 - [Modulation Type] to ‘3’.
– Set Parameter 82 - [Ground I Lvl] to 100%.
– Set Parameter 85 - [Droop] to 5% for current sharing of the AFEs.
– Set Parameter 86 - [PWM Synch] to ‘1’ to reduce circulating currents
between AFEs connected to the same DC bus and fed from the same
power source.
• If one of the paralleled AFEs is to be isolated from the AC and DC
voltages, you must isolate the AC input and DC output. The AC input
can be isolated with a circuit breaker or a disconnect switch. Contactors
are not suitable for isolating the AC input because they cannot be locked
in the safe position. The DC output can be isolated with a disconnect. A
load isolation switch or safety isolation switch can be used to isolate the
precharging circuit from the AC input.
• Each AFE must use a separate precharging circuit, precharging control
switch, DC bus output fusing, and main contactor.
Each AFE controls its own precharging and main contactor. Therefore, it
is possible to disconnect the AFE when other parallel AFEs are powered
up but not modulating.
• The fault relay of both AFEs must be interlocked with each other, such
that both AFEs are disabled (not running) when either AFE is faulted.