LSIS Master-K K1000S - Page 196

Chapter 15 The PID function of K200S MASTER-K
15-11
The figure 15.13 shows the PV and MV of PI control system when the windup occurs. As
shown as the figure 15.13, the actuator is saturated because of the large initial deviation.
The integral term increase until the PV reaches to the SV (deviation = 0), and then start to
decrease while the PC is larger than SV (deviation < 0). However, the MV keeps the
saturated status until the integral term is small enough to cancel the windup of actuator.
As the result of the windup, the actuator will output positive value for a while after the PV
reached to the SV, and the system show a large overshoot. A large initial deviation, load
disturbance, or mis-operation can cause windup of actuator.
Fig. 15.13 An example of integral windup
PV
SV
Time
PV
MV
SV
Time
MV (without windup)
MV (with windup)
Integral term
Proportional term