Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 274)

274 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 4 Motor Control
SLAT Maximum Mode
Choose SLAT Maximum mode when material direction and speed reference is
considered “Reverse” and a negative speed reference value for the Speed
Regulator. The Speed Regulator output then creates a negative Torque Reference
command value.
In SLAT Maximum mode, a speed reference is typically configured to force the
speed regulator into saturation (the speed reference is slightly below the speed
feedback which is equivalent to maintain planned line speed). In this scenario the
drive follows the torque reference until there is breakage or slippage in the
application.
In SLAT Maximum mode, the drive switches from Torque mode to Speed mode
when either one of the two following conditions occur.
• The output of the speed regulator becomes more than the torque
reference. This is the same condition that exists in Maximum Torque/
Speed mode without SLAT features.
Or
• The speed error becomes positive (the speed feedback becomes less than
the speed reference). This forces the control into speed regulator mode, a
condition called Forced Speed Mode (FSM).
By forcing the drive to enter FSM, the transition occurs earlier than it would have
if the reaction was triggered at the very point that the torque reference value in
speed mode is mathematically more than the value in torque mode, generally
resulting in less velocity overshoot.
P314 [SLAT Err Stpt] and P315 [SLAT Dwell Time] allow for setting some
hysteresis for turning off the forced speed mode. They are set to 0 as default so
that there is no hysteresis. In SLAT maximum mode, [SLAT Err Stpt] sets how
much more the speed feedback (algebraically sign sensitive) should be than the
speed reference before turning off the forced speed mode. [SLAT Dwell Time]
sets how long the speed error must be less than the SLAT error set point before
turning off the forced speed mode.
At the time that the drive switches from torque mode to speed mode the speed
regulator output is loaded with the value from the torque reference to create a
smooth transition.
In order for the drive to switch from speed mode back to torque mode, forced
speed mode (if active) must first be turned off. FSM will turn off when the speed
error is less than the SLAT error set point for the SLAT dwell time.