Rockwell Automation Publication 8720MC-RM001K-EN-P - September 2018 55
Connect the 8720MC-RPS Unit Chapter 5
Regenerative Mode Input Power Diagrams
It is possible to select the 8720MC-RPS units based on regenerative power
when only regenerated power of the unit integrating converter and inverter is
used. See the figures on page 56
and page 57 for example diagrams. In these
examples, the 8720MC-RPS unit is used as a converter for regenerative mode
power only.
Observe the following Regenerative mode installation best practices:
• Rating of regenerative power of the 8720MC-RPS is less than rated
power in the instantaneous rating and continuous rating.
• When the rectifier portion of the inverter is composed of a thyristor, the
CR snubber circuit between anode and cathode of thyristor can become
overloaded. Therefore, treating time for regenerative power must be
within five seconds for three minutes. Because the current ICR flowing
through the CR snubber circuit in the power regeneration mode is
represented by the following formula, verify the specifications of CR
snubber circuit.
• Connect the line reactor (ACL) unit of 3% impedance toward inverter
rating with the AC input line of inverter. Without the line reactor unit,
excessive circulating current flows between the 8720MC-RPS units.
• Even during the power running, current is supplied from the
8720MC-RPS unit to DC-bus proportionally to the impedance ratio of
both reactors at the 8720MC-RPS unit and inverter. This current must
not exceed the rating of the 8720MC-RPS unit.
• Set the parameter of the FWD Current Limit (U.001) to zero (0).
• Set the parameter of the Discharging Function Enable (F.017) to zero
(OFF).
• Set the DC-bus voltage to start power regeneration to the parameter of
the DC-bus voltage reference (U.000).
• Open the PR1, PR2, and PR3 terminals for connecting the precharge/
discharge resistor. Because these terminals are open, the unit does not
perform precharge/discharge operations. Precharge/discharge must be
performed on the inverter side.
• Connect the READY signal of the inverter to PWR.
I [A] = (8–0.03 • R [Ω) •
CR
C [μF]
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