Danfoss VLT AutomationDrive FC 300 Programming Manual page 99

Parameter Descriptions
7-06 Speed PID Lowpass Filter Time
Range:
Application
dependent
*
3 3
98
Function:
[1.0 - Set a time constant for the speed control
100.0 low-pass filter. The low-pass filter
ms] improves steady-state performance and
dampens oscillations on the feedback
signal. This is an advantage if there is a
great amount on noise in the system, see
illustration below. For example, if a time
constant (τ) of 100 ms is programmed, the
cut-off frequency for the low-pass filter
will be 1/0.1= 10 RAD/sec., corresponding
to (10/2 x π) = 1.6 Hz. The PID regulator
only regulates a feedback signal that
varies by a frequency of less than 1.6 Hz. If
the feedback signal varies by a higher
frequency than 1.6 Hz, the PID regulator
does not react.
Practical settings of 7-06 Speed PID
Lowpass Filter Time taken from the number
of pulses per revolutions from encoder:
Encoder PPR 7-06 Speed PID
Lowpass Filter Time
512 10 ms
1024 5 ms
2048 2 ms
4096 1 ms
Note that severe filtering can be
detrimental to dynamic performance.
This parameter is used with 1-00 Configu-
ration Mode Speed closed loop [1] and
Torque [2] control.
The filter time in flux sensorless must be
adjusted to 3-5 ms.
MG.33.MB.02 - VLT
FC 300 Programming Guide
Feedback
Disturbed feedback signal
Feedback
Filtered feedback signal
®
is a registered Danfoss trademark
0.6
Lowpass lter
f = 10 Hz
g
0.6
t (Sec.)
t (Sec.)