Danfoss VLT 2800 Design Manual page 101

Programming
NOTICE
If the frequency converter is running a the current limit
before the required start frequency is obtained, the
process regulator is not activated. For the regulator to
be activated anyway, the start frequency must be lower
to the required output frequency. This can be done
during operation.
PID start frequency may not be set higher than f
using pipe fill mode.
440 Proces PID proportioanl gain
Value:
0.0 - 10.00
Function:
The proportional gain indicates the number of times the
deviation between the setpoint and the feedback signal is
to be applied.
Description of choice:
Quick regulation is obtained by a high gain, but if the gain
is too high, the process may become unstable due to
overshoot.
441 Process PID integration time
Value:
0.01 - 9999.99 (OFF)
Function:
The integrator provides an increasing gain at a constant
error between the reference/setpoint and the feedback
signal. The greater the error, the quicker the integrator
frequency contribution increases. The integral time is the
time needed by the integrator to make the same change
as the proportional gain.
Description of choice:
Quick regulation is obtained at a short integral time.
However, this time may become too short, which can
make the process unstable due to overswing. If the
integral time is long, major deviations from the required
setpoint may occur, since the process regulator takes a
long time to regulate in relation to a given error.
442 Process PID differentiation time
Value:
0.00 (OFF) - 10.00 s
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 differen-
tiator. The gain is proportional to the speed at which the
deviation changes.
MG27E402
Design Guide
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
Value:
if
MIN 5.0 - 50.0
Function:
It is possible to set a limit for the differentiator gain. The
differentiator gain increases if there are fast changes.
Therefore it's necessary to limit this gain. Thereby a pure
differentiator gain is obtained at slow changes and a
0.01
constant differentiator gain where quick changes to the
deviation occur.
Description of choice:
Select a differentiator gain limit as required.
444
Value:
0.02 - 10.00
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
OFF
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 is 1/0.1=10 RAD/s, corresponding to (10/2 x
π)=1.6 Hz. The process regulator thus only regulates 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 is dampened by the lowpass filter.
445
Value:
Off (DISABLE)
OK - same direction
(OK-same direction)
OK - both directions
(OK-both directions)
DC brake and start
0.00 s
(DC-BRAKE BEF. START)
Function:
This function enables catching 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 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
Description of choice:
Select [0] Disable if this function is not required.
Danfoss A/S © Rev. May/2014 All rights reserved.
Process PID diff. gain limit
Process PID lowpass filter time
Flying start
.
MAX
5.0
4 4
0.02
[0]
[1]
[2]
[3]
99