B. Fine-tuned PID controller The individual effect of K
P
, K
i
and K
d
summarized in Table 3.2 can be very useful in fine tuning
of PID controller. Beginning with the values of K
P
, K
i
and K
d
obtained from Z-N step response
method, unit step response for different combination of K
P
, K
i
and K
d
were observed [9].
Closed loop
Response
Overshoot Settling time
Steady-state
Error
Increase K
p
Increase
Small Increase
Decrease
Increase K
i
Increase
Increase
Large Decrease
Increase k
d
Increase
Decrease
Minor change
Table 3. 3 Effect of Kp ,Ki and Kd in . Fine-tuning technique
C. Cohen Coon Method The Cohen-Coon method is a more complex version of the Ziegler-Nichols method [9] .This
method is more sensitive than the Ziegler-Nichols method. The controller parameters with this
method are given in table3.4.
Table 3. 4 Cohen Coon PID controller parameter for first order plus dead time model
For PID controller
For PID controller
K
c
=0.1466
k
i
= 0.00383(
=37.9381)
K
d
=0.9308(
=6.3492)
Thus, the controller transfer function is:
Controller
P
(
⁄ )(
⁄ )(
⁄
)
PI
(
⁄ )(
⁄ )(
⁄
)
( )
⁄
( )
⁄
PID
(
⁄ )(
⁄ )
( )
⁄
( )
⁄
( )
⁄
Fuzzy PID Based Temperature Control of Electric Furnace for Glass Tempering Process M.Sc. Thesis, Addis Ababa University, December 2016 37
( )
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