Rockwell Automation WebPak 3000 DC Drive Application Workbook Version 1.1 - Manual (Page 22)

3-12 WebPak 3000 DC Drive Application Workbook, Version 1.1
3.3.3 Selecting the Outer Loop Type
þ
To select the outer loop type:
▲
Set OCL TYPE (P.818). The choices are:
CASCADE - The outer control loop trim signal is added to the speed loop
reference. The dynamics of the outer control loop and the inner speed loop
are interactive in the cascade mode.
PARALLEL - The outer control loop trim signal is used as the input level for both
the high and low current limits of the speed loop PI block. The speed loop
operates in a limit mode, and the limited output of speed loop PI block is set by
the dynamics of the outer control loop.
Certain processes and electro-mechanical systems may favor the parallel
type of outer control loop operation because of its apparent simpler design.
However, the cascade design, when used with dynamic gain profiling, will
typically provide better overall dynamic response and stability over a greater
range of machine and process characteristics.
þ If OCL TYPE (P.818) = PARALLEL , an offset to drive the speed regulation
loop into limit is required.
▲ Set OCL PARALLEL OFFSET (P.810). This is typically set to 10% of TOP
LINE SPEED , which would infer a setting for P.810 of 409 counts.
3.3.4 Current Compounding
Some drives, when operating as speed regulators, may have application requirements
for a softening or a drooping of speed with motor load. The current compounding
function uses a scaled percentage of
CML FEEDBACK (P.397), which is subtracted from
the SPEED RAMP OUTPUT (P.199).
Current compounding should be used only when no outer control loop has been
selected.
þ
To use current compounding:
▲
Set CURRENT COMPOUNDING (P.209) to specify the trim that is subtracted from
the speed reference based on motor load.
CURRENT COMPOUND TP (P.293) reads the percentage of CML FEEDBACK (P.397) that is
subtracted from the speed reference.
Range: CASCADE , PARALLEL P.818 =
Range: -4095 to 4095 COUNTS (4095 = TOP LINE SPEED ) P.810 = COUNTS
Current Compounding Example
Requirement: Change the motor speed by 5% when the motor is operating at 50% full load
and at
TOP LINE SPEED .
5% motor speed x 100 = 10% = setting of CURRENT COMPOUNDING (P.209)
50% motor load
Range: -50% to 50% OF THE MOTOR LOAD P.209 = %