Danfoss VLT AQUA Drive FC 200 Programming Manual page 140

Parameter Description
3.17.6 20-9* PID Controller
This group provides the ability to manually adjust this PID
controller. By adjusting the PID controller parameters, the
3 3
control performance may be improved. See the
Introduction to VLT AQUA Drive in the VLT AQUA Drive
Design Guide, MG20N for guidelines on adjusting the PID
Controller parameters.
20-91 PID Anti Windup
Option: Function:
[0] Off [0] Off The integrator will continue to change value also
after output has reached one of the extremes. This can
afterwards cause a delay of change of the output of the
controller.
[1] On [1] On The integrator will be locked if the output of the
built-in PID controller has reached one of the extremes
(min or max value) and therefore not able to add
further change to the value of the process parameter
controlled. This allows the controller to respond more
quickly when it again can control the system.
20-93 PID Proportional Gain
Range:
0.50 [0 - 10 ] The proportional gain indicates the number of
*
If (Error x Gain) jumps with a value equal to what is set in
3-03 Maximum Reference, the PID controller will try to
change the output speed equal to what is set in
4-13 Motor Speed High Limit [RPM]/4-14 Motor Speed High
Limit [Hz] but in practice of course limited by this setting.
The proportional band (error causing output to change
from 0‒100%) can be calculated by means of the formula:
(
1
Proportional Gain
NOTICE!
Always set the desired value for 3-03 Maximum Reference
before setting the values for the PID Controller in
parameter group 20-9* PID Controller.
20-94 PID Integral Time
Range:
20 [0.01 -
s 10000 s]
*
3-114
Function:
times the error between the setpoint and the
feedback signal is to be applied.
)
× ( Max Reference )
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.
MG20O622 - VLT
®
VLT AQUA Drive Programming Guide
20-94 PID Integral Time
Range:
8 s
*
10000 s]
20-95 PID Differentiation Time
Range:
0 s [0 -
*
10 s]
20-96 PID Diff. Gain Limit
Range:
5 [1 -
*
50 ]
®
is a registered Danfoss trademark
Function:
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.
[0.01 -
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 a value that is too large is used,
the adjustable frequency drive's output frequency
may become unstable.
Differentiation time is useful in situations where
extremely fast adjustable frequency drive 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/
waste water applications. Therefore, it is generally
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 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).