ABB ACSM1 - Page 26

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26
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
To get a fast dynamic torque or speed response with a speed
feedback value other than (0) Estimated (see parameter 22.01
SPEED
FB SEL
), the actual speed filter time must be set to zero.
22.02 SPEED ACT
FTIME
Speed controller tuning
For the most demanding applications, the P- and I-parts of the speed controller of the drive can be
tuned either manually or automatically. See parameter 28.16 PI TUNE MODE.
If it is necessary to adjust acceleration (deceleration) compensation, it must be done manually.
Acceleration (deceleration) compensation can be used to improve the
speed control dynamic reference change (when the speed ramp times
> 0). In order to compensate inertia during acceleration, a derivative of
the speed reference is added to the output of the speed controller.
Set the derivation time for acceleration (deceleration) compensation.
The value should be proportional to the total inertia of the load and
motor, i.e. approximately 50…100% of the mechanical time constant
(t
mech
). See the mechanical time constant equation in section Speed
filtering on page 26.
26.08 ACC COMP
DERTIME