Rockwell Automation SB3000 High Pwr SB3000 AC Pwr Modules (RCS) - Manual (Page 63)

Theory of Operation B-3
B.2 SB3000 Regulator
The main purpose of the SB3000 regulator is to maintain the proper voltage on the DC
bus through the use of a vector algorithm executed in the PMI Processor.
The application task in the UDC module controlling the SB3000 Power Module passes
the desired DC bus voltage reference command to the PMI Processor in register
102/1102. The PMI Processor uses proportional-integral-derivative (PID) logic to
calculate DC bus current in response to the voltage reference and error values. See
figure B.2.
The commanded current is actually made up of two parts: Iq and Id. The Iq current is
in phase with the AC line voltage when motoring and is 180 degrees out of phase with
the AC line when regenerating. The Id current leads the AC line voltage by 90
degrees. The Iq current is the real current that powers the DC bus. The Id current is
the reactive current that produces the leading power factor.
The PMI Processor uses the AC line period to determine the frequency to command.
It uses the offset between the zero crossing of the AC line and the commanded zero
crossing to determine the angle offset. The AC line frequency may change up to 1 Hz
per second.