Rockwell Automation 20D PowerFlex 700S AC Drives with Phase II Control Reference Manual User 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

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

Off

Speed Error > 0

Speed Error < SLAT Setpoint

for SLAT Time

FSM State Controller

P119 SLAT Error Setpoint

P120 SLAT Dwell Time