Rockwell Automation Publication 750-RM100A-EN-P - August 2019 99
Droop Control for Parallel Operation of PowerFlex 755TM AFE Bus Supplies Chapter 10
This results in a smooth and progressive curve for the DC bus voltage reference.
Figure 43 - DC Bus Voltage Reference
Derating for Voltage Boost
In standalone operation (not parallel), PowerFlex® 755TM bus supplies are
designed to operate with the DC bus voltage reference equal to the optimized or
minimum DC bus level. This optimization maximizes energy efficiency. Because
the Droop function raises the DC bus voltage reference, you must account for
this when sizing the bus supplies.
Consider the DC bus voltage reference at full load in the regenerating direction
with default values. The reference at that operating point is:
Minimum DC Bus Voltage + (No Load Droop Gain/100) x Minimum DC Bus
Voltage + (Full Load Droop Gain/100) x Minimum DC Bus Voltage
Or
Minimum DC Bus Voltage x [1 + (No Load Droop Gain/100) + (Full Load
Droop Gain/100)]
Consider a 480V
rms
example with default values in the gain parameters.
• Minimum DC Bus Voltage = 480 x SQRT(2) x 1.02 = 692.4V DC
•No Load Droop Gain = 1%
• Full Load Droop Gain = 5%
• Trans Droop Cur = 50%
• DC bus voltage reference = 692.4 x (1 + 0.01 + 0.05) = 733.9V DC
This is a considerable boost to the DC bus voltage. For information about
derating for this, see PowerFlex 750-Series Products with TotalFORCE® Control,
publication 750-TD100
.
Regenerating
Motoring
Zero Current +Trans Droop
Current
-Trans Droop
Current
-Full Load
Current
+Full Load
Current
Active Current
Zero Current
DC Bus Voltage
Reference
Minimum DC Bus Voltage
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