Danfoss VLT Micro Drive FC 51 Design Manual page 21

Product Overview
For example, consider a pump application where the speed
of a pump is to be controlled so that the static pressure in
a pipe is constant. The static pressure value is supplied to
the frequency converter as the setpoint reference. A static
pressure sensor measures the actual static pressure in the
pipe and supplies this data to the frequency converter as a
feedback signal. If the feedback signal is greater than the
+
Reference
S
_
Feedback
Illustration 3.3 Control Structure Closed Loop
While the default values for the closed-loop controller of
the frequency converter often provide satisfactory
performance, the control of the system can often be
optimized by adjusting parameters.
MG02K402
Design Guide
PI
*[-1]
7-30 PI
Normal/Inverse
Control
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setpoint reference, the frequency converter slows the
pump down to reduce the pressure. In a similar way, if the
pipe pressure is lower than the setpoint reference, the
frequency converter automatically speeds the pump up to
increase the pressure provided by the pump.
100%
0%
100%
-100%
P 4-10
Motor speed
direction
To motor
Scale to
speed control
19
3 3