P 20-81
PID Normal/Inverse
Control
PID
Ref.
Handling
Feedback
Handling
Scale to
speed
P 4-10
Motor speed
direction
To motor
control
(Illustra-
tion)
(Illustra-
tion)
130BA359.12
100%
0%
-100%
100%
*[-1]
_
+
Illustration 2.26 Block Diagram of Closed Loop Controller
While the default values for the frequency converter’s closed loop controller often provides satisfactory performance, the
control of the system can often be optimised by adjusting some of the closed loop controller’s parameters. It is also
possible to autotune the PI constants.
2.8.7 Feedback Handling
Setpoint 1
P 20-21
Setpoint 2
P 20-22
Setpoint 3
P 20-23
Feedback 1 Source
P 20-00
Feedback 2 Source
P 20-03
Feedback 3 Source
P 20-06
Feedback conv.
P 20-01
Feedback conv.
P 20-04
Feedback conv.
P 20-07
Feedback 1
Feedback 2
Feedback 3
Feedback
Feedback Function
P 20-20
Multi setpoint min.
Multi setpoint max.
Feedback 1 only
Feedback 2 only
Feedback 3 only
Sum (1+2+3)
Difference (1-2)
Average (1+2+3)
Minimum (1|2|3)
Maximum (1|2|3)
Setpoint to
Reference
Handling
0%
0%
0%
0%
130BA354.12
Illustration 2.27 Block Diagram of Feedback Signal Processing
Feedback handling can be configured to work with
applications requiring advanced control, such as multiple
setpoints and multiple feedbacks. 3 types of control are
common.
Single Zone, Single Setpoint
Single Zone, Single Setpoint is a basic configuration.
Setpoint 1 is added to any other reference (if any, see
Reference Handling) and the feedback signal is selected
using
20-20 Feedback Function
.
Multi Zone, Single Setpoint
Multi Zone Single Setpoint uses 2 or 3 feedback sensors,
but only one setpoint. The feedbacks can be added,
subtracted (only feedback 1 and 2) or averaged. In
addition, the maximum or minimum value may be used.
Setpoint 1 is used exclusively in this configuration.
If
[13] Multi Setpoint Min
is selected, the setpoint/feedback
pair with the largest difference controls the speed of the
frequency converter.
[14] Multi Setpoint Maximum
attempts
to keep all zones at or below their respective setpoints,
Introduction to VLT® HVAC D...
Design Guide
36
Danfoss A/S © Rev. 06/2014 All rights reserved.
MG11BC02
2
2
