Par. Group 7 - Controllers; Process Pid Feedback; Speed Pid Lowpass Filter Time - Danfoss VLT CDS 303 Operating Instructions Manual

Parameter Descriptions

6.8 Par. Group 7 - Controllers

7-06 Speed PID Lowpass Filter Time

Range:
Size
related - 100
*
ms]
6 6
NOTICE!
Severe filtering can be detrimental to dynamic
performance.
This parameter is used with parameter 1-00 Configuration
Mode [1] Speed closed loop and [2] Torque control.
The filter time in flux sensorless must be adjusted to
3-5 ms.
76
Function:
[0.1 Set a time constant for the speed control low-
pass filter. The low-pass filter 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 Figure 6.10. 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/s., 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 parameter 7-06 Speed PID
Lowpass Filter Time taken from the number of
pulses per revolutions from encoder:
Encoder PPR Parameter 7-06 Spee
d PID Lowpass Filter
Time
512 10 ms
1024 5 ms
2048 2 ms
4096 1 ms
Danfoss A/S © Rev. 2013-07-03 All rights reserved.
®
VLT Compressor Drives CDS 302/CDS 303
Feedback
Disturbed feedback signal
Feedback
Filtered feedback signal
Figure 6.10 Feedback Signal

6.8.1 7-2* Process PID Feedback

Select the feedback sources for the Process PID Control,
and how this feedback should be handled.
0.6
Lowpass lter
f = 10 Hz
g
0.6
t (Sec.)
t (Sec.)
MG34M422