Rockwell Automation Publication 750-RM100A-EN-P - August 2019 97
Droop Control for Parallel Operation of PowerFlex 755TM AFE Bus Supplies Chapter 10
Modes of Operation
There are two modes of operation: Linear and Nonlinear. The default mode of
operation is Linear. To change the mode of operation in the PowerFlex 755T,
adjust parameter 13:350 [DroopCtrlModeSel].
Linear Mode
The Linear Mode uses a piecewise linear function to determine the DC bus
voltage reference. In this function, the active current reference is the input (X-
axis). The DC bus voltage reference is the output (Y-axis).
Figure 40 - Linear Mode
Minimum DC bus voltage reference is the same as the automatic (optimized)
DC bus voltage reference. This is 2% above the peak of the naturally rectified
voltage level. For example, if the incoming voltage is 480 V
rms
, then minimum
DC Bus voltage reference is 692.4V DC (VDC = VRMS x SQRT(2) x 1.02).
There are four regions of operation. The Motoring Full Load region is between
positive ‘Trans Droop Current’ and positive full load current. The Motoring No
Load region is between zero current and positive ‘Trans Droop Current’. The
Regen No Load region is between zero current and negative ‘Trans Droop
Current’. The Regen Full Load region is between negative ‘Trans Droop Current’
and negative full load current. The value in parameter 13:353 [Trans Droop Cur]
defines the positive and negative ‘Trans Droop Current’ points on the X-axis.
You determine the horizontal boundaries of the regions by entering the value of
parameter 13:353 [Trans Droop Cur]. This value determines the locations of the
inflection points on DC bus voltage droop curve.
In the Motoring Full Load and Regen Full Load regions, the value in parameter
13:351 [FullLd DroopGain] determines the slope of the curve. Set the value of
this parameter as percent increase in DC bus voltage reference (percent of
minimum DC bus voltage) over the positive current range (zero load to full
load).
Regenerating
Motoring
Zero Current +Trans Droop
Current
-Trans Droop
Current
-Full Load
Current
+Full Load
Current
Active Current
Zero Current
Minimum DC
Bus Voltage
DC Bus
Voltage
Reference
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