Rockwell Automation 20D PowerFlex 700S AC Drives with Phase II Control Reference Manual - Manual (Page 154)

154 Rockwell Automation Publication PFLEX-RM003E-EN-E - January 2011
Chapter 1 Detailed Drive Operation
Current Limit Stop
When a current limit stop is commanded, parameter 157 [Logic Ctrl State], bit 6
“CurrLim Stop” is set. Then a zero speed reference command is sent into the
speed regulator, bypassing the ramp and speed trim.
Speed Error
The summed speed reference becomes parameter 301 [Motor Speed Ref ]. Then
the filtered motor speed feedback (parameter 300 [Motor Spd Fdbk]) is
subtracted from the motor speed reference to create a speed error.
There is a lead/lag filter that can be used to filter the motor speed feedback. The
filter is setup by parameters 93 [SRegFB Filt Gain] and 94 [SReg FB Filt BW].
The filtered speed feedback is configured in parameter 71 [Filtered SpdFdbk].
The speed error can be filtered by a low pass filter by adjusting parameter 89 [Spd
Err Filt BW]. For more information on lead/lag and low pass filters see
Lead-Lag
Filter on page 50 .
Servo Lock
Servo lock is used for servo or positioning applications. The effect of servo lock is
to increase stiffness of the speed response to a load disturbance. It behaves like a
position regulator with velocity feed forward, but without the pulse accuracy of a
true position regulator. The output of the servo lock block is summed with the
filtered speed error.
Parameter 85 [Servo Lock Gain] sets the gain of an additional integrator in the
speed regulator. The units of [Servo Lock Gain] are radians/second. Gain should
0
1
157 06
0
Logic Ctrl State
from Speed Limits to Speed Error
(CurrLim Stop)
93
94
89
301
71
300
100
SReg FB Filt Gain
SReg FB Filt BW
Motor Spd Fdbk
from Current
Limit Stop
from
Feedback
to Servo
Lock
Motor Speed Ref
Speed Error
Spd Err Filt BW
2 nd Order
LPass
Filter
+
-
Lead Lag
(kn * s)+ wn
s + wn
Filtered SpdFdbk