Rockwell Automation 1395 DC Drive, 800-1250 Hp, FRN 5.XX-9.30 - Manual (Page 57)

Chapter 3
Functional Description
3-24
functional again, it would be possible to switch back to it through one of
two methods:
1. Change the value of the feedback device parameter (Parameter 621)
to the original feedback type. NOTE: If the drive is running while
this change is made, the drive will check to make certain the feedback
from the primary feedback device is within the tach loss window. If it
is, the switch will be honored and the parameter values will be
restored to their previous values. If not, the switchover will not be
allowed.
2. Issue a “Clear Faults” command to the Drive. The fault will be
cleared, and the Drive will be reset to it’s previous feedback device,
gains and field flux level. Note that this command is only honored
when the Drive is not running.
Current Reference Contro l (Circle 9)
The output of the Torque Reference Select block is applied to a limiting
function block. Forward Bridge Current Limit (Parameter 663) and
Reverse Bridge Current Limit (Parameter 664), specify the largest
allowable positive and negative motor armature current that can be
commanded. The limited current is then applied to a Torque Taper
function block. Start Taper Speed (Parameter 665) defines the motor speed
above which torque tapering will begin. End Taper Speed (Parameter 666)
defines the speed above which the Minimum Taper Current (Parameter
667) will be used as the upper limit for armature current reference. The
output of these function blocks is the Armature Current Reference
(Parameter 111). This value is scaled using Parameters 611 and 615, and
summed with Armature Current Feedback. The difference between the
reference and feedback value is filtered and modified through a P/I Control
Function. Armature Loop Proportional Gain (Parameter 735) determines
the proportional gain of the current regulator. Armature Loop Integral
Gain (Parameter 736) determines the integral gain. Parameter 734 is used
to linearize the armature current loop for discontinuous current operation.
The output of the Armature Current P/I Control block is converted to a
time and sent to the armature SCR bridge.
Field Flux Control (Circle 11 and 12 )
Provides information for field weakening, flux reference and field flux
linearization. Several parameters are required to develop this information:
– Feedback Device Type (Parameter 621) provides the Flux Reference
Selection block with feedback information.
– Flux Mode Select (Parameter 627) enables options in the flux control
module.
– Field Flux Reference (Parameter 676) defines the highest flux reference
that can be applied to the motor field.