ABB ACSM1 - Page 25

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25
Speed filtering
The measured speed always has a small ripple because of electrical and mechanical interferences,
couplings and encoder resolution (i.e. small pulse number). A small ripple is acceptable as long as
it does not affect the speed control chain. The interferences in the speed measurement can be
filtered with a speed error filter or with an actual speed filter.
Reducing the ripple with filters may cause speed controller tuning problems. A long filter time
constant and fast acceleration time contradict one another. A very long filter time results in unstable
control.
If the used speed reference changes rapidly (servo application), use
the speed error filter to filter the possible interferences in the speed
measurement. In this case the speed error filter is more suitable than
the actual speed filter:
- Set the filter time constant.
26.06 SPD ERR FTIME
If the used speed reference remains constant, use the actual speed
filter to filter the possible interferences in the speed measurement. In
this case the actual speed filter is more suitable than the speed error
filter:
- Set the filter time constant.
If there are substantial interferences in the speed measurement, the
filter time constant should be proportional to the total inertia of the load
and motor, i.e. approximately 10…30% of the mechanical time
constant
t
mech
= (n
nom
/ T
nom
) × J
tot
× 2π / 60, where
J
tot
= total inertia of the load and motor (the gear ratio between the
load and the motor must be taken into account)
n
nom
= motor nominal speed
T
nom
= motor nominal torque
22.02 SPEED ACT
FTIME
Manual speed controller tuning
Select the following signals to be monitored with the DriveStudio Data
Logger or Monitoring Window:
- 1.01 SPEED ACT, filtered actual speed
- 1.06 TORQUE, motor torque.
Start the motor with a small speed reference.
Give a speed reference step and monitor the response. Repeat the test for few speed reference
steps across the whole speed range:
Set the speed ramp time to a suitable value (according to the used
application).
25.03 ACC TIME
Set a suitable speed step (according to the used application): 10% or
20% of the maximum speed of the drive. Accept the new value by
pressing the Set new reference button.