Allen-Bradley PowerFlex 70 Reference Manual page 175

Figure 39
Load Step (Decrease)
Speed Feedback
Sum Mode
Configuring the drive in this mode allows an external torque input to be summed
with the torque command generated by the speed regulator. The drive requires
both a speed reference and a torque reference to be linked. This mode can be used
for applications that have precise speed changes with critical time constraints. If
the torque requirement and timing is known for a given speed change, then the
external torque input can be used to preload the integrator. The timing of the
speed change and the application of an external torque command change must be
coordinated for this mode to be useful. The sum mode will then work as a feed
forward to the torque regulator.
Zero Torque Mode
Operation in zero torque mode allows the motor to be fully fluxed and ready to
rotate when a speed command or torque command is given. For a cyclical
application where through put is a high priority this mode can be used. The
control logic can select zero torque during the "rest" portion of a machine cycle
instead of stopping the drive. When the cycle start occurs, instead of issuing a
start to the drive, a speed regulate mode can be selected. The drive will then
immediately accelerate the motor without the need for "flux up" time.
Important: Zero Torque may excessively heat the motor if operated in this mode
for extended periods of time. No load or flux current is still present
when the drive is operating in zero torque mode. A motor with an
extended speed range or separate cooling methods (blower) may be
required.
Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013
Internal Torque Command
308
RPM
Speed/Torque Select
At Speed Relay
175