Rockwell Automation 1336E IMPACT Adjustable Frequency AC Drive User Manual V 1-4.XX - Manual (Page 355)

Control Block Diagrams B-17
The 1336 IMPACT drive takes the speed reference that you specify to
the drive and compares that value to the value of the speed feedback
that is coming from the motor. The drive tries to make the two values
match as close as possible by sending a speed error value to the speed
PI regulator. The speed PI regulator uses the Kp (proportional) and Ki
(integral) gains to adjust the torque reference value that is sent to the
motor to try to get the actual speed of the motor as close to the speed
you specified as possible. This can be shown as:
The Kp and Ki gains are set during the auto-tune procedure. Once you
find gains that provide a good speed of response for your system
without making your system unstable, you should not change the Kp
and Ki parameters. The Kp and Ki gains are covered in the Inertia
Test portion of Chapter 13, Understanding the Auto-tuning
Procedure. The following information about Kp is also provided to
show what happens if you are not using the proper gains for your
system.
The following information is provided about Ki:
Speed Reference
Speed Regulator
Motor
Encoder
Speed Feedback
+
–
Speed Error
Kp
+
+
Ki
If Kp is: Then:
Too low
The response time decreases. This means that it takes the regulator a
longer time to get the speed feedback value close to the speed
reference value that you specified.
Too high
A torque ripple can be produced. If you have an encoder on your
system, the torque ripple can be produced typically when Kp is around
50. If you do not have an encoder on your system, the maximum is less
than 50.
0
The speed PI regulator is strictly an integral regulator. This causes
unstable operation.
If Ki is: Then:
Too low
The time that it takes to recover from a speed or load disturbance
increases. This means that the regulator takes a longer time to get the
speed feedback value close to the speed reference value that you
specified.
Too high Your system will not be stable, and it may oscillate.
0 The speed PI regulator is strictly a proportional regulator.