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PID Controls
+
Ref.
Handling
% [unit]
_
Feedback
Handling
% [unit]
Illustration 16.2 Process PID Control Diagram
16.2.1 Process PID Control Parameters
The following parameters are relevant for the process control
Parameter
Description of function
Parameter 7-20 Process CL
Selects from which input the process PID gets its feedback.
Feedback 1 Resource
Parameter 7-22 Process CL
Optional: Determines if and from where the process PID gets an additional feedback signal. If an additional
Feedback 2 Resource
feedback source is selected, the 2 feedback signals are added before being used in the process PID
control.
Parameter 7-30 Process PID
Under [0] normal operation, the process control responds with an increase of the motor speed if the
Normal/ Inverse Control
feedback lower than the reference. In the same situation, but under [1] inverse operation, the process
control responds with a decreasing motor speed.
Parameter 7-31 Process PID
The anti-windup function ensures that when either a frequency limit or a torque limit is reached, the
Anti Windup
integrator is set to a gain that corresponds to the actual frequency. This function avoids integrating on an
error that cannot be compensated with a speed change. Disable this function by selecting [0] Off.
Parameter 7-32 Process PID
In some applications, reaching the required speed/setpoint can take a long time. In such cases, it is
Start Speed
beneficial to set a fixed motor speed from the frequency converter before the process control is activated.
Set the fixed motor speed by setting a process PID start value (speed) in parameter 7-32 Process PID Start
Speed.
Parameter 7-33 Process PID
The higher the value, the quicker the control. However, too large a value can lead to oscillations.
Proportional Gain
Parameter 7-34 Process PID
Eliminates steady state speed error. Lower value means quick reaction. However, too small a value can lead
Integral Time
to oscillations.
Parameter 7-35 Process PID
Provides a gain proportional to the rate of feedback change. A setting of 0 disables the differentiator.
Differentiation Time
Parameter 7-36 Process PID
If there are quick changes in reference or feedback in a given application, the differentiator gain can be
Diff. Gain Limit
limited to allow setting of a reasonable differentiation time for slow error changes.
Parameter 7-38 Process PID
In applications where there is a good and approximately linear correlation between the process reference
Feed Forward Factor
and the motor speed necessary for obtaining that reference, the feed forward factor can be used to
achieve better dynamic performance of the process PID control.
MG37N102
Design Guide
Process PID
P 7-38
Feed forward
%
%
[unit]
[speed]
PID
*(-1)
P 7-30
normal/inverse
Danfoss A/S © 6/2016 All rights reserved.
100%
0%
0%
Scale to
speed
-100%
100%
-100%
P 4-10
Motor speed
direction
To motor
control
16
16
147
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