which could be jeopardized by vibrations, for example, a
crane with a heavy load then you can limit the bandwidth
in which the PID controller should function.
32-64 PID
Bandwidth
of 300 makes a limitation of 30% possible. The
build-up of a vibration is thus prevented since the control
is only moved to with 30% of the calculated set value.
However, then it is necessary also to use the feed-forward
part of the controller in order to achieve the
corresponding control.
4.4 Optimizing your Controller Settings
Step-by-Step
Before adjusting the controller parameters it is important
to determine which controller behavior is to be achieved.
NOTE
The drive elements must never be operated outside of the
technical specifications. Thus the maximum acceleration is
determined by the “weakest” drive element.
-
“Stiff” axis: the fastest reaction possible is mainly
influenced by the
Proportional Factor
. You can
judge the results on the basis of the velocity
graph.
-
Damping of vibrations is mainly influenced by the
Derivative Value
. The results can best be assessed
in the velocity graph.
-
Temporary (static) deviations in position are
mainly reduced by the
Integral Factor
and can
best be judged on the basis of the positioning
graph.
For best results use the functions in the
Tune Oscilloscope
for this purpose; these help you to evaluate and optimize
the PID controller on the basis of graphs of the set and
actual curves.
However, it is recommended only to change one value at a
time and subsequently determining the improvement with
a
Testrun
.
Click on
Controller
→
Parameter
→
Axis and select the
frequency converter, of which you are currently adjusting
the settings.
4.4.1 Ten Steps for Optimum Control
The following procedure will optimize your controller
settings in most applications:
1.
Make sure that you have specified correct values
for VLT AutomationDrive
3-03 Maximum Reference
,
as well as
32-80 Maximum Velocity (Encoder)
, the
encoder type and resolution in
32-00 Incremental
Signal Type
and
32-01 Incremental Resolution
, and
32-81 Shortest Ramp
. If these settings change
again at a later point, the controller may need
optimizing again.
Par. #
Typical Settings
3-03
Maximum Reference
1500,000
32-80
Max. Velocity (Encoder)
1500
32-00
Incremental Signal Type
[1] RS422
32-01
Incremental Resolution
1024
32-81
Incremental Resolution
1.000
2.
Set
32-67 Max. Tolerated Position Error
to a very
high value e.g. 1000000 to avoid getting the error
108 during the following tests.
NOTE
To avoid damaging the system, make sure to set
32-67 Max. Tolerated Position Error
within the limits of the
system, because the position error monitoring is not active
with extremely high values.
3.
Optimize the Velocity Feed-forward control: Click
on Execute Testrun and Start a testrun with
following parameter settings:
32-6* PID-Controller
32-60 Proportional factor
0
32-61 Derivative factor
0
32-65 Velocity Feed-Forward
100
32-66 Acceleration Feed-Forward
0
View the velocity profiles: If the Actual Velocity profile is
lower than the Commanded Velocity profile, increase
Velocity Feed-forward
and
→
Start
the testrun again. Of
course if the Actual Velocity profile is higher than the
specified Commanded Velocity you should decrease
Velocity Feed-forward
.
Run successive test runs until the two velocity profiles
shown in the Testrun graph have the same maximum
value.
Velocity Feed-forward
is now optimized, save the current
value.
4.
In systems with large inertia and/or rapid changes
in the reference velocity it is a good idea to use
and optimize the Acceleration Feed-forward
control (make sure the inertial load is connected
when optimizing this parameter):
Execute a Testrun with KPROP=0, KDER=0,
KINT=0, FFACC=0, and FFVEL at the optimized
value found above. Use the highest possible
acceleration setting. If
32-81 Shortest Ramp
is
adjusted properly an acceleration value of 100
and a deceleration value of 100 should be
sufficient. Start out with a low setting of
Acceleration Feed-forward
approx. 10.
Optimizing the PID controll...
MCO 305 Operating Instructions
22
MG.33.K3.02 - VLT
®
is a registered Danfoss trademark
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