Feedback Handling - Danfoss VLT Refrigeration Drive FC 103 Design Manual

Product Overview

2.4.5 Feedback Handling

Feedback handling can be configured to work with
applications requiring advanced control, such as multiple
setpoints and multiple types of feedback (see
Illustration 2.13.
3 types of control are common:
Single zone, single setpoint
This control type is a basic feedback configuration.
Setpoint 1 is added to any other reference (if any) and the
feedback signal is selected.
Multi-zone, single setpoint
This control type uses 2 or 3 feedback sensors but only 1
setpoint. The feedback can be added, subtracted, or
averaged. In addition, the maximum or minimum value can
be used. Setpoint 1 is used exclusively in this configu-
ration.
Setpoint 1
P 20-21
Setpoint 2
P 20-22
Setpoint 3
P 20-23
Feedback conv.
Feedback 1 Source
P 20-01
P 20-00
Feedback conv.
Feedback 2 Source
P 20-04
P 20-03
Feedback conv.
Feedback 3 Source
P 20-07
P 20-06
Illustration 2.13 Block Diagram of Feedback Signal Processing
MG16G202
Design Guide
Multi-zone, setpoint/feedback
The setpoint/feedback pair with the largest difference
controls the speed of the frequency converter. The
maximum attempts to keep all zones at or below their
respective setpoints, while minimum attempts to keep all
zones at or above their respective setpoints.
Example
A 2-zone, 2-setpoint application. Zone 1 setpoint is 15 bar,
and the feedback is 5.5 bar. Zone 2 setpoint is 4.4 bar, and
the feedback is 4.6 bar. If maximum is selected, the zone 2
setpoint and feedback are sent to the PID controller, since
it has the smaller difference (feedback is higher than
setpoint, resulting in a negative difference). If minimum is
selected, the zone 1 setpoint and feedback is sent to the
PID controller, since it has the larger difference (feedback is
lower than setpoint, resulting in a positive difference).
Multi setpoint min.
Multi setpoint max.
Feedback 1 only
Feedback 1
Feedback 2 only
Feedback 3 only
Sum (1+2+3)
Feedback 2
Di erence (1-2)
Average (1+2+3)
Minimum (1|2|3)
Maximum (1|2|3)
Feedback 3
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Setpoint to
0% Reference
Handling
0%
0%
Feedback
0%
Feedback Function
P 20-20
2 2
23