LSIS Master-K K200S - Page 197

Chapter 15 The PID function of K200S MASTER-K
15-12
There are several methods to avoid the windup of actuator. The most popular two
methods are adding another feedback system to actuator, and modeling the actuator. The
figure 15.14 shows the block diagram of the anti-windup control system using the model
of actuator.
Fig. 15.14 The block diagram of anti-windup control system
As shown in the figure 15.14, the anti-windup system feedback the multiplication of gain
(1/Tt) and Es to the input of integral term. The Es is obtained as the difference value
between actuator output (U) and manipulation value of PID controller (MV). The Tt of the
feedback gain is tracking time constant, and it is in inverse proportion with the resetting
speed of integral term. Smaller Tt will cancel the windup of actuator faster, but too small
Tt can cause anti-windup operation even in derivation operation. The figure 15.15 shows
several Tt value and PV in the PI control system.
Fig. 15.15 The PV output characteristics with different Tt values
K × Td
K Actuator
1 / Tt
k / Ti
+
+
+
E = SV -PV
E = -PV
MV U
Actuator model
Es
–
+
Tt = 3
Tt = 2
Tt = 1
Tt = 0.1
Time
PV
SV