Danfoss VLT FCD 300 Series Design Manual page 96

®
VLT Decentral FCD 300 Design Guide
Description of choice:
Quick regulation is obtained through a short integral time. However, if
this time is too short, it can make the process unstable. If the integral
time is long, major deviations from the required reference may occur,
since the process regulator will take long to regulate if an error has oc-
curred.
419 Speed PID differential time
Value:
0.00 (OFF) - 200.00 ms
Function:
The differentiator does not react to a constant error. It only makes a
contribution when the error changes. The quicker the error changes, the
stronger the gain from the differentiator will be. The contribution is pro-
portional to the speed at which errors change.
Description of choice:
Quick control is obtained by a long differential time. However, if this time
is too long, it can make the process unstable. When the differential time
is 0 ms, the D-function is not active.
420 Speed PID D- gain limit
Value:
5.0 - 50.0
Function:
It is possible to set a limit for the gain provided by the differentiator. Since
the D-gain increases at higher frequencies, limiting the gain may be use-
ful. This enables obtaining a pure D-gain at low frequencies and a
constant D-gain at higher frequencies.
Description of choice:
Select the required gain limit.
421 Speed PID lowpass filter time
Value:
20 - 500 ms
Function:
Noise in the feedback signal is dampened by a first order lowpass filter
to reduce the noise's impact on the regulation. This might be an advant-
age, e.g. if there is a great amount of noise on the signal. See drawing.
Description of choice:
If a time constant (t) of 100 ms is programmed, the cut-off frequency for
the lowpass filter will be 1/0.1 = 10 RAD/sec., corresponding to (10 / 2
x π) = 1.6 Hz. The PID regulator will then only regulate a feedback signal
that varies with a frequency of less than 1.6 Hz. If the feedback signal
varies by a higher frequency than 1.6 Hz, it will be dampened by the
lowpass filter.
423
Value:
20.00 ms
0.0 - 999.0 V
Function:
Parameters 423-428 are used when in parameter 101
teristic a selection has been made of
is possible to determine a U/f characteristic on the basis of four definable
voltages and three frequencies. The voltage at 0 Hz is set in parameter
Start voltage
133
5.0
Description of choice:
Set the output voltage (U1) that is to match the first output frequency
(F1), parameter 424
424
100 ms
Value:
0.0 - par. 426
Function:
See parameter 423
Description of choice:
Set the output frequency (F1) that is to match the first output voltage
(U1), parameter 423
425
Value:
0.0 - 999.0 V
Function:
See parameter 423
Description of choice:
Set the output voltage (U2) that is to match the second output frequency
(F2), parameter 426
426
Value:
Par. 424
Function:
See parameter 423
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MG.90.S1.02 - VLT is a registered Danfoss trademark
U1 voltage
Special motor characteristic
.
F1 frequency
.
F1 frequency
F2 frequency
Par. 104
U1 voltage
.
U1 voltage .
U2 voltage
U1 voltage .
F2 frequency.
F2 frequency
F1 frequency - par. 428 F3 frequency
U1 voltage .
4 Programming
par. 103
4
Torque charac-
[8]. It
Motor frequency
par. 103
Motor
Par. 104
frequency
95