Rockwell Automation 20D PowerFlex 700S AC Drives with Phase II Control Reference Manual - Manual (Page 169)

Rockwell Automation Publication PFLEX-RM003E-EN-E - January 2011 169
Detailed Drive Operation Chapter 1
• The speed error becomes positive (the speed feedback becomes less than
the speed reference). This is forced speed mode. By forcing the drive to
enter speed mode, the transition occurs earlier than it would have in the
maximum torque mode, resulting in less velocity overshoot.
Parameter 119 [SLAT ErrorSetpnt] and parameter 120 [SLAT Dwell Time]
allow you to set 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
ErrorSetpnt] sets how much more the speed feedback 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 to torque mode, forced speed
mode (if active) must first be turned off. Forced speed mode will turn off when
the speed error is less than the SLAT error set point for the SLAT dwell time.
With default parameter settings, this will occur when the speed error becomes
negative.
When forced speed mode is off, the drive will switch back to torque mode when
the speed regulator output becomes less than the torque reference. This is the
same condition that exists in maximum torque mode.
Application
Dependant Speed
Reference Bias
Motor Speed
Feedback
+
-
Speed Error
PI
Regulator
Speed Regulator
Output (SRO)
Max
Select
External Torque
Reference (ETR)
Internal Torque
Reference (ITR)
Off
Forced Speed
Mode (FSM)
FSM = On
Low Pass
Filter
On Off
Speed Error > 0
Speed Error < SLAT Setpoint
for SLAT Time
FSM State Controller
P119 SLAT Error Setpoint
P120 SLAT Dwell Time