setpoint may occur, since the process regulator will take a long time to
regulate in relation to a given error.
442
Process PID differentiation time
Value:
0.00 (OFF) - 10.00 sec.
0.00 sec.
Function:
The differentiator does not react to a constant error. It only makes a gain
when an error changes. The quicker the deviation changes, the stronger
the gain from the differentiator. The gain is proportional to the speed at
which the deviation changes.
Description of choice:
Quick regulation is obtained with a long differentiation time. However,
this time may become too long, which can make the process unstable
due to overswing.
443
Process PID diff. gain limit
Value:
5.0 - 50.0
5.0
Function:
It is possible to set a limit for the differentiator gain. The differentiator
gain will increase if there are fast changes, which is why it can be bene-
ficial to limit this gain. Thereby a pure differentiator gain is obtained at
slow changes and a constant differentiator gain where quick changes to
the deviation occur.
Description of choice:
Select a differentiator gain limit as required.
444
Process PID lowpass filter time
Value:
0.02 - 10.00
0.02
Function:
Noise in the feedback signal is dampened by a first order lowpass filter
to reduce the noise's impact on the process regulation. This can be an
advantage e.g. if there is a lot of noise on the signal.
Description of choice:
Select the required time constant (t). If a time constant (t) of 0.1 s 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 process regu-
lator will thus only regulate a feedback signal that varies by a frequency
lower 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.
445
Flying start
Value:
Off (DISABLE)
[0]
OK - same direction
(OK-same direction)
[1]
OK - both directions
(OK-both directions)
[2]
DC brake and start
(DC-BRAKE BEF. START)
[3]
Function:
This function makes it possible to 'catch' a rotating motor shaft, which is
no longer controlled by the adjustable frequency drive, e.g. because of a
mains drop-out. The function is activated each time a start command is
enabled. For the adjustable frequency drive to be able to 'catch' the ro-
tating motor shaft, the motor speed must be lower than the frequency
that corresponds to the frequency in parameter 202
Output frequency,
high limit, f
MAX
.
Description of choice:
Select
Disable
[0] if this function is not required.
Select
OK - same direction
[1] if the motor shaft is only able to rotate in
the same direction when cutting in.
OK - same direction
[1] should be
selected if in parameter 200
Output frequency range
a selection has been
of
Clockwise only
.
Select
OK - both directions
[2] if the motor is able to rotate in both di-
rections when cutting in.
Select
DC brake and start
[3] if the adjustable frequency drive is to be
able to brake the motor using the DC brake first, followed by start. It is
assumed that parameters 126-127/132
DC brake
are enabled. In the case
of higher 'Windmilling' (rotating motor) effects, the adjustable frequency
drive is not able to 'catch' a rotating motor without selecting
DC brake
and start
.
Limitations:
-
Too low inertia will lead to load acceleration, which can be dan-
gerous or prevent correct catching of a rotating motor. Use the
DC brake instead.
-
If the load is driven, e.g. by 'Windmilling' (rotating motor) ef-
fects, the unit may cut out because of overvoltage.
-
Flying start does not work at lower values than 250 rpm.
451
Speed PID feedforward factor
Value:
0 - 500 %
100 %
Function:
This parameter is only active if in parameter 100
Configuration
the se-
lection made is
Speed regulation, closed loop
. The FF function sends a
larger or smaller part of the reference signal outside the PID controller in
such a way that the PID controller only has an influence on part of the
control signal. Any change to the set point will thus have a direct effect
on the motor speed. The FF factor provides high dynamism when chang-
ing the set point and less overswing.
Description of choice:
The required % value can be selected in the interval f
MIN
- f
MAX
. Values
over 100 % are used if the set point variations are only small.
452
Controller range
Value:
0 - 200 %
10 %
Function:
This parameter is only active if in parameter 100
Configuration
the se-
lection made is
Speed regulation, closed loop
.
The controller range (bandwidth) limits the output from the PID controller
as a % of motor frequency f
M,N
.
Description of choice:
The required % value can be selected for motor frequency f
M,N
. If the
controller range is reduced the speed variations will be less during initial
tuning.
VLT
®
Decentral FCD 300 Design Guide
4 Programming
MG.90.S1.02 - VLT
®
is a registered Danfoss trademark
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