Feedforward Control - Omron CS1W-LC001 Operation Manual

Examples of Applied Control Types
5-2-2

Feedforward Control

Example
002-086
Secondary Auto/Manual
Before the influence of disturbances such as load fluctuation appears in the
process result, disturbance is detected beforehand to correct MV so that its
influence is canceled. Feedforward control is used in combination with
feedback control.
Function block used: Lead/Delay (Block Model 147)
Disturbance
PV
The output of the Lead/Delay block is added to the MV output of the
Advanced PID block.
Note 1 Though cascade control can suppress the influence of disturbance on the
secondary loop, it cannot suppress the influence of disturbance on the
primary loop. Whereas, feedforward control can suppress the influence of
disturbance on the primary loop in cascade control.
Set Point
+
SP
−
PV
Note 2 A general feedforward control model is obtained by dividing the disturbance
characteristics by the process characteristics. The transfer function of
feedforward control is as follows when the disturbance characteristic is
K2/(T+T2•s) as its transfer function is approximated by the first-order lag, and
the process characteristic is K1/(1+T1•s) as its transfer function is
approximated by the first-order lag:
K2/K1 x (1+T1•s) / (1+T2•s)
where,
T1: Time constant of process
T2: Time constant of disturbance
K1: Process gain
001-085
• The MV tracking switch turns OFF when PID2
is set to Auto, and turns ON when PID2 is set
to Manual.
MV tracking switch
Lead/Delay
Block Model 147
MV compensation (ITEM074)
MV
Advanced PID
Block Model 012
Disturbance
Feedforward control
PID control
Section
Disturbance
characteristics
−
Process
+
characteristics
+
+
5-2
Control
output
165