Danfoss VLT AQUA Drive FC 202 Programming Manual page 143

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
Introduction to VLT AQUA Drive in the VLT
202 Design Guide for guidelines on adjusting the PID
Controller parameters.
20-91 PID Anti Windup
Option: Function:
[0] Off The integrator continues 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 The integrator is locked if the output of the built-in PID
controller has reached one of the extremes (min or max
value) and therefore is 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: Function:
2 [0 - 10 ] The proportional gain indicates the number of
*
times the error between the set point and the
feedback signal is to be applied.
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], 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
Max Reference
×
Proportional Gain
NOTICE
Always set the desired value for
parameter 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: Function:
8 s [0.01 - Over time, the integrator accumulates a contri-
*
10000 s] 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.
MG20O702
Programming Guide
20-94 PID Integral Time
Range:
®
AQUA Drive FC
20-95 PID Differentiation Time
Range:
0 s
*
20-96 PID Diff. Gain Limit
Range:
5
*
Danfoss A/S © Rev. 2014-01-21 All rights reserved.
Function:
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 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:
[0 - 10 The differentiator monitors the rate of change of
s] 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
generally best to leave this parameter at 0 or OFF.
Function:
[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
parameter 20-95 PID Differentiation Time is not set
to OFF (0 s).
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