Pid Gain Adjustments & Control Characteristics - Hitachi L100 300 User Manual

2-2 PID Gain Adjustments & Control Characteristics
The optimal gain factors of PID vary from condition to condition, and from system to system. That
means it is necessary to set those parameters by taking into account the individual control characteristics
of your particular system. The following are the characteristics that are required for a good PID control:
l
Stable performance
l
Quick response
l
Small steady-state deviation
You adjust each parameter K
increase each gain (K
response. But if you increase them too much, the control will be unstable, because the feedback value is
continuously increasing and decreasing, which leads to an oscillation of the control. In the worst case the
system is led to a divergence mode. (Refer to Fig. 2-4)
Following are the procedures to adjust each parameter.
(1) After changing target,
(2) Target and feedback
(3) Even after increasing Kp, response is still slow
Target
Controlled
object
Target
Controlled
object
Fig. 2-4 Example of good control and bad control (in case of step response)
, T and K
p i d
, K , K ) parameter (= decrease Integration time : T
p i d
response is slow
response is quick but unstable
do not become equal
become equal after unstable vibration
it is still unstable
NG : Divergence
time
Good Control
time
SJ100/L100 / PID / 6
inside the stable performance area. Generally, when you
--- Increase P-gain (K
--- Decrease P-gain (K
--- Decrease Integration time (T
--- Increase Integration time (T
--- Increase D-gain (K
--- Decrease D-gain (K
Target
Controlled
object
NG : Damped oscillation
Controlled
object
Target
), you can obtain quick
i
)
p
)
p
)
d
)
d
time
NG : Slow response, big
steady state deviation
time
)
i
)
i