Danfoss VLT AQUA Drive FC 202 Programming Manual page 170

Parameter Description
3.17.5 20-9* PID Controller
Use these parameters to adjust the PID controller manually.
By adjusting the PID controller parameters, the control
performance may be improved. See the VLT
3 3
FC 202 Design Guide for guidelines on adjusting the PID
controller parameters.
20-91 PID Anti Windup
Option: Function:
NOTICE
Option [1] On is activated automatically, if 1 of
the following options is selected in parameters
in parameter group 21-** Ext. Closed Loop: [0]
Normal, [X] Enabled Ext CLX PID.
[0] Off The integrator continues to change value also after
output has reached 1 of the extremes. This can
afterwards cause a delay of change of the output of
the controller.
[1] On The integrator is locked if the output of the built-in
*
PID controller has reached 1 of the extremes
(minimum or maximum value) and therefore is not
able to add further changes to the value of the
process parameter controlled. This allows the controller
to respond more quickly when it can control the
system again.
20-93 PID Proportional Gain
Range:
2 [0 - 10 ] The proportional gain indicates the number of
*
If (Error x Gain) jumps with a value equal to what is set in
parameter 3-03 Maximum Reference, the PID controller tries
to change the output speed equal to what is set in
parameter 4-13 Motor Speed High Limit [RPM]/
parameter 4-14 Motor Speed High Limit [Hz]. However, in
practice it is limited by this setting.
The proportional band (error causing output to change
from 0–100%) can be calculated with the formula:
1
Proportional Gain
NOTICE
Set the value for parameter 3-03 Maximum Reference
before setting the values for the PID controller in
parameter group 20-9* PID Controller.
168
VLT
®
Function:
times the error between the setpoint and the
feedback signal is to be applied.
× Max Reference
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®
AQUA Drive FC 202
20-94 PID Integral Time
Range:
8 s [0.01 -
*
10000 s]
AQUA Drive
20-95 PID Differentiation Time
Range:
0 s [0 - 10
*
s]
20-96 PID Diff. Gain Limit
Range:
5 [1 -
*
50 ]
Function:
The integrator accumulates a contribution to the
output from the PID controller as long as there
is a deviation between the reference/setpoint
and feedback signals. The contribution is propor-
tional 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 10000, the controller acts as
a pure proportional controller with a P-band
based on the value set in parameter 20-93 PID
Proportional Gain. When no deviation is present,
the output from the proportional controller is 0.
Function:
The differentiator monitors the rate of change of
the feedback. If the feedback is changing quickly,
it adjusts 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 in 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
water/wastewater applications. Therefore, it is best
to leave this parameter at 0 or OFF.
Function:
The differential function of a PID controller
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 large
change in the PID controller output. This parameter
limits the maximum effect that the PID controller
differential function can produce. A smaller value
reduces the maximum effect of the PID controller
differential function.
This parameter is only active when
parameter 20-95 PID Differentiation Time is not set
to OFF (0 s).
MG20OB02