Rockwell Automation SB3000 AC Power Modules - Manual (Page 69)

Theory of Operation C-5
C.2.1 Leading Power Factor Operation
The regulator has the capability to operate with a leading power factor. This allows the
regulator to calculate the Id current based on the capacity that is left over in the
SB3000 Power Module rating after the Iq current has been determined.
If the UDC application task provides a leading power factor current reference value
(IPF_REF%) in register 103/1103, the vector algorithm can compensate for a lagging
power factor in the total AC line load with the second component of the current vector
(Id). The Id current is calculated based on the value of Iq current and the current
reference value in register 103/1103. The leading power factor current reference value
is limited to not exceed the SB3000 Power Module’s current limit rating. When Id
current is near zero, due to a small load on the DC bus, it can approach the reference
value. As Iq current increases, Id current decreases. A status bit indicates when the
power factor current is being limited.
If capacity is left over after power has been supplied to the inverter load, the vector
algorithm can produce VARS (volt-amperes reactive) with a leading power factor to
compensate for other machines with lagging power factors on the same AC line. The
Id current is limited not to exceed the rectifier rating. The VARS produced will be
reported in register 211/1211.
Assuming power factor current is not being limited, Id current is calculated based on
the Iq current and IPF_REF%. See figure C.3. The amount of VAR that is produced
will be displayed in the feedback data.
When Iq current is near zero
because there is negligible load
on the DC bus, Id current can
be near the full value of
IPF_REF%. When Iq current becomes larger,
Id current becomes smaller. When Iq current becomes greater
than IPF_REF, Id current is
reduced to zero.
Figure C.3 – Leading Power Factor
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