8.2.17 FeedForward
P3.13.4.1 Feedforward 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 Feedforward control). RSI feedforward 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 measurements of the
disturbance, we can try to compensate for this
disturbance by simple feedforward 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.
9099
Feedforward control
Pos. Description
1 Level ref
2 Level control
3 Outflow control
Related information
8.1.14 Group 3.13: PID Controller
156
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