Danfoss VLT FC 103 Programming Manual page 121

Parameter Description
20-94 PID Integral Time
Range:
30 [0.01 -
s 10000 s]
*
3 3
20-95 PID Differentiation Time
Range:
0.0 [0.00 =
s Off -
*
10.00 s]
20-96 PID Diff. Gain Limit
Range:
5 [1 - The differential function of a PID Controller
*
50 ] responds to the rate of change of the feedback. As
a result, an abrupt change in the feedback can
cause the differential function to make a very large
change in the PID Controller's output. This
parameter limits the maximum effect that the PID
Controller's differential function can produce. A
smaller value reduces the maximum effect of the
PID Controller's differential function.
This parameter is only active when 20-95 PID Differ-
entiation Time is not set to OFF (0 s).
120
Function:
Over time, the integrator accumulates a contri-
bution to the output from the PID controller as
long as there is a deviation between the
Reference/Setpoint and feedback signals. The
contribution is proportional to the size of the
deviation. This ensures that the deviation (error)
approaches zero.
Quick response on any deviation is obtained
when the integral time is set to a low value.
Setting it too low, however, may cause the
control to become unstable.
The value set, is the time needed for the
integrator to add the same contribution as the
proportional for a certain deviation.
If the value is set to 10,000, the controller will act
as a pure proportional controller with a P-band
based on the value set in 20-93 PID Proportional
Gain. When no deviation is present, the output
from the proportional controller will be 0.
Function:
The differentiator monitors the rate of change of
the feedback. If the feedback is changing
quickly, it will adjust the output of the PID
Controller to reduce the rate of change of the
feedback. Quick PID Controller response is
obtained when this value is large. However, if
too large of a value is used, the frequency
converter's output frequency may become
unstable.
Differentiation time is useful is situations where
extremely fast frequency converter response and
precise speed control are required. It can be
difficult to adjust this for proper system control.
Differentiation time is not commonly used in
VLT Refrigeration Drive applications. Therefore, it
is generally best to leave this parameter at 0 or
OFF.
Function:
MG16H102 - VLT
®
VLT Refrigeration Drive Programming Guide
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is a registered Danfoss trademark