Vacon 100X series, Applications Manual

Page: 147 / 172

Parameters vacon • 144
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6
6.2.17 FeedForward
P3.13.4.1 F
EEDFORWARD FUNCTION
Feedforward usually needs accurate process models, but in some simple cases a gain + offset
type of feedforward is enough. The feedforward part does not use any feedback measurements
of the actual controlled process value (water level in the example on page 144). Vacon feedfor-
ward control uses other measurements which are indirectly affecting the controlled process
value.
Example 1:
Controlling the water level of a tank by means of flow control. The desired water level has been
defined as a setpoint and the actual level as feedback. The control signal acts on the incoming
flow.
The outflow could be thought of as a disturbance that can be measured. Based on the mea-
surements of the disturbance, we can try to compensate for this disturbance by simple feed-
forward control (gain and offset) which is added to the PID output.
This way the controller would react much faster to changes in the outflow than if you just had
measured the level.
Figure 51. Feedforward control
PID
+ +
LT
FT
9099.emf
FFW
Level ref
Level control
Outflow
control