Rockwell Automation 20D PowerFlex 700S with Phase I Control Reference Manual - Manual (Page 123)

Rockwell Automation Publication PFLEX-RM002D-EN-E - August 2013 123
Detail Drive Configuration and Operation Chapter 1
There is a lead/lag filter that can be used to filter the motor speed feedback. The
filter is setup by parameters 95 [Sreg FB Filt Gain] and 94 [Sreg FB Filt BW].
The filtered speed feedback is seen in parameter 71 [Filtered SpdFdbk].
The speed error is filtered by a low pass filter by adjusting [Spd Err Filt BW].
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 rad/sec. Gain should
normally be set to less than 1/3 speed regulator bandwidth, or for the desired
response. Set [Servo Lock Gain] to zero to disable Servo Lock.
Speed Regulation Anti-Backup
Parameter 84 [SpdReg Anti Bckup] modifies the drive's response to the speed
reference. With the value minimized, the drive will follow the reference very
closely, minimizing error, which is desirable for typical process applications.
However, it will exhibit some over-shoot and under-shoot. Increasing the value of
this term decreases the over-shoot and under-shoot, which is desirable where
back-up cannot be tolerated. However, this tends to increase the following error:
93
94
89
301
71
300
100
SReg FB Filt Gain
SReg FB Filt BW
Motor Spd Fdbk
Motor Speed Ref
Speed Error
Spd Err Filt BW
2 nd Order
LPass
Filter
+
-
Lead Lag
(kn * s)+ wn
s + wn
Filtered SpdFdbk
+
85
ServoLck
ks
s
Servo Lock Gain