Mitsubishi Electric MELSEC iQ-R Series User Manual page 336

■One-degree-of-freedom PID control and two-degree-of-freedom PID control
• General PID control is called one-degree-of freedom PID control. In the one-degree-of freedom PID control, when PID
constants to improve the "response to the change of the set value (SV)" have been set, the "response to the disturbance"
degrades. Conversely, when PID constants to improve the "response to the disturbance" have been set, the "response to
the change of the set value (SV)" degrades.
• In the two-degree-of-freedom PID control, a manipulated value (MV) is determined considering a set value (SV) and
variation amount. In the two-degree-of-freedom PID control, the "response to the change of the set value (SV)" and the
"response to the disturbance" can be compatible with each other.
Added function for two-degree-of-freedom
Set value
(SV)
-
+
The appropriate setting of , , and  in the above figure can achieve the optimum control. However, required parameter
settings increase and PID constants can hardly be automatically set by the auto tuning function for complete two-degree-
offreedom PID control. Therefore, the temperature control module operates in the simple two-degree-of-freedom PID control
for which parameters have been simplified.
APPX
334
Appendix 4 PID
+
+
+ -
1
1 + T · s
I
PID control
+
1
K (1 + )
P
T · s
Manipulated
I
+
value (MV)
+
K · T · s
P D
1 + T · s
D
-
Object to be
controlled
Disturbance D
G(s)
Temperature
process value (PV)