Control Structure Closed Loop - Danfoss VLT HVAC Basic Drive FC 101 Design Manual

Product Overview
Local reference forces the configuration mode to open-
loop, independent on the setting of
parameter 1-00 Configuration Mode.
Local reference is restored at power-down.

3.2.4 Control Structure Closed Loop

The internal controller allows the frequency converter to
become a part of the controlled system. The frequency
converter receives a feedback signal from a sensor in the
system. It then compares this feedback to a setpoint
reference value and determines the error, if any, between
these 2 signals. It then adjusts the speed of the motor to
correct this error.
+
Reference
S
_
Feedback
Illustration 3.19 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.
MG18C702
Design Guide
PI
*[-1]
7-30 PI
Normal/Inverse
Control
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For example, consider a pump application where the speed
of a pump is to be controlled to ensure a constant static
pressure in a pipe. 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
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
control
speed
27
3 3