Danfoss VLT FCD 311 Design Guide

VLT
®
FCD Series
which can make the process unstable due to over-
swing.
443
443 Process PID diff. gain limit
(PROC. DIFF.GAIN)
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 beneficial to limit
this gain. Thereby a pure differentiator gain is ob-
tained 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
444 Process PID lowpass filter time
(PROC 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 fre-
quency for the lowpass filter will be 1/0.1 = 10 RAD/
sec., corresponding to (10 / 2 x
 ) = 1.6 Hz. The
process regulator 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
445 Flying start
(FLYINGSTART )
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 fre-
quency converter, e.g. because of a mains drop-out.
The function is activated each time a start command
is enabled. For the frequency converter to be able to
’catch’ the rotating 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 directions when cutting in.
Select DC brake and start [3] if the frequency con-
verter is to be able to brake the motor using the DC
brake first, followed by start. It is assumed that pa-
rameters 126-127/132 DC brake are enabled. In the
case of higher ’Windmilling’ (rotating motor) effects,
the frequency converter is not able to ’catch’ a rotat-
ing motor without selecting DC brake and start.
Limitations:
- Too low inertia will lead to load acceleration,
which can be dangerous or prevent correct catch-
ing of a rotating motor. Use the DC brake instead.
- If the load is driven, e.g. by ’Windmilling’ (rotating
motor) effects, the unit may cut out because of
overvoltage.
- Flying start does not work at lower values than
250 rpm.
451
451 Speed PID feedforward factor
(FEEDFORWARD FACT)
Value:
0 - 500 %
✭ 100 %
Function:
This parameter is only active if in parameter 100
Configuration the selection made is Speed regula-
tion, 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
✭
= factory setting. () = display text [] = value for use in communication via serial communication port
MG.04.A1.02 - VLT is a registered Danfoss trade mark
92

Danfoss VLT FCD 311 Specifications

General

Brand	Danfoss
Model	VLT FCD 311
Category	DC Drives
Language	English