5.6 CONTROL ELEMENTS
A general form of a PID regulator in the s domain is shown below.
5
The following terms apply to the block diagram:
•
y is the process signal
•
r is the setpoint signal
•
w is the tracking signal
•
u is the regulator output
•
K is the proportional gain
•
b is the setpoint weighting
•
T
is the derivative time constant
d
•
N is the derivative limit
•
T
is the integral time constant
i
•
T
is the anti-windup time constant
t
•
s is the domain
In discrete form, the equations for the regulator are:
Where T
is the sampling time and AW is a flag which enables anti-windup. The incremental form of the above equation is:
S
5-108
Figure 5–42: PID BLOCK DIAGRAM
e k ( )
r k ( ) y k ( )
=
–
p k ( )
K br k ( ) y k ( )
(
)
=
–
T
d
d k ( )
----------------------- -
×
d k 1
(
)
=
–
T
NT
+
d
S
u k ( )
p k ( )
i k ( )
d k ( )
=
+
+
e k ( )
KT
T
S
(
)
i k ( )
---------------------- -
------
i k
1
+
=
+
+
T
i
Du k ( )
u k ( ) u k 1
=
Dp k ( )
=
C30 Controller System
kT
N
d
----------------------- -
×
(
y k ( ) y k 1
(
–
–
–
T
NT
+
d
S
S
×
(
w k ( ) u k ( )
)
×
AW
–
T
t
(
)
–
–
Di k ( )
Dd k ( )
+
+
5 SETTINGS
)
)
(EQ 5.1)
(EQ 5.2)
GE Multilin