Danfoss VLT AutomationDrive FC 300, Design Manual, Page: 44 / 296

3.4.7 Process PID Control Parameters
The following parameters are relevant for the process control
Parameter Description of function
7-20 Process CL Feedback 1
Resource Selects from which input the Process PID should get its feedback.
7-22 Process CL Feedback 2
Resource Optional: Determines if and from where the process PID should get an additional feedback signal. If an
additional feedback source is selected, the two feedback signals are added together before being used in
the process PID control.
7-30 Process PID Normal/
Inverse Control Under [0] normal operation , the process control responds with an increase of the motor speed if the
feedback lower than the reference. In the same situation, but under [1] inverse operation , the process
control responds with a decreasing motor speed.
7-31 Process PID Anti Windup The anti-windup function ensures that when either a frequency limit or a torque limit is reached, the
integrator is set to a gain that corresponds to the actual frequency. This avoids integrating on an error
that cannot be compensated for by means of a speed change. Disable this function by selecting
[0] Off .
7-32 Process PID Controller
Start Value In some applications, reaching the required speed/setpoint can take a long time. In such cases, it is
beneficial to set a fixed motor speed from the adjustable frequency drive before the process control is
activated. This is done by setting a process PID start value (speed) in
7-32 Process PID Controller Start Value .
7-33 Process PID Proportional
Gain The higher the value, the quicker the control. However, too large a value may lead to oscillations.
7-34 Process PID Integral
Time Eliminates steady state speed error. Lower value means quick reaction. However, too small a value may
lead to oscillations.
7-35 Process PID Differen-
tiation Time Provides a gain proportional to the rate of feedback change. A setting of zero disables the differentiator.
7-36 Process PID Differen-
tiation Gain Limit If there are quick changes in reference or feedback in a given application, the differentiator gain can be
limited to allow setting of a reasonable differentiation time for slow error changes.
7-38 Process PID Feed
Forward Factor In applications where there is a good and approximately linear correlation between the process reference
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.
5-54 Pulse Filter Time
Constant #29 (Pulse term.
29), 5-59 Pulse Filter Time
Constant #33 (Pulse term.
33), 6-16 Terminal 53 Filter
Time Constant (analog term
53), 6-26 Terminal 54 Filter
Time Constant (analog term.
54) If there are oscillations of the current/voltage feedback signal, these can be dampened by means of a low-
pass filter. This time constant represents the speed limit of the ripples occurring on the feedback signal.
Example: If the low-pass filter has been set to 0.1 s, the limit speed is 10 RAD/s (the reciprocal of 0.1 s),
corresponding to (10/(2 x π))=1.6 Hz. This means that all currents/voltages that vary by more than 1.6
oscillations per s are damped by the filter. The control is only carried out on a feedback signal that varies
by a frequency (speed) of less than 1.6 Hz.
The low-pass filter improves steady-state performance, but selecting too large a filter time deteriorates the
dynamic performance of the process PID control.
Table 3.10 Process Control Parameters
Product Introduction Design Guide
42 Danfoss A/S © Rev. 2014-02-10 All rights reserved. MG34S222
3 3