Rockwell Automation SB3000 Configuration and Programming - Manual (Page 101)

SB3000 Control Algorithm C-1
A
PPENDIX
C
SB3000 Control Algorithm
SB3000 Synchronous Rectifiers regulate DC bus voltage using a vector control
algorithm. This algorithm, which is executed in the PMI processor, is also referred to
as the minor loop. (The major control loop is executed in the AutoMax processor.)
The UDC application control task passes the desired DC bus voltage reference
command to the PMI Processor in register 102/1102. The PMI Processor uses PID
(proportional/integral/derivative) logic to calculate DC bus current (referred to as Iq) in
response to the voltage reference and voltage error. In motoring quadrants, the Iq
component of current is in phase with the AC line voltage. In regenerating quadrants,
the Iq component is 180 degrees out of phase with the AC line.
The PMI Processor uses the AC line period to determine the frequency to command.
The offset between the zero crossing of the AC line and the commanded zero
crossing is used to determine the angle offset. The AC line frequency may change by
up to 1 Hz per second.
If the UDC application task provides a leading power factor current reference in
register 103/1103, the vector algorithm can compensate for a lagging power factor in
the load inverter with the second component of the current vector, referred to as Id. Id
is calculated from the value of Iq and the reference in register 103/1103. When Iq is
near zero due to a small load on the DC bus, Id can approach the reference value. As
Iq becomes larger, Id becomes smaller.
If capacity is left over after power has been supplied to the load, the vector algorithm
can produce reactive power (VARS) with a leading power factor to compensate for
other machines with lagging power factors on the same AC line. Id will be limited not to
exceed the rectifier rating. The VARS produced will be reported in register 211/1211.