LG Industrial Systems GLOFA GM6 Series, Руководство пользователя

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Chapter 15. The PID functions
15-14
15.2.2.3 D control
The continuous formula of derivative term is as following;
dt
dy
KTd D D
dt
d
N
Td
− = + ×
N : high frequency noise depression ration
y : the object to be controlled (PV)
The digitized formula is as following (Use Tustin approximation method)
[ ]
) 1 ( ) (
2
2
) 1 (
2
2
) (
− −
+
− −
+
−
=
n y n y
hN Td
KTdN
n D
hN Td
hN Td
n D
15.2.2.4 Pseudo code of PID control
The pseudo code of PID control is as following;
Step 1 : Get constants that are used for PID operation
Ti
h
K Bi
× =
: integral gain
) 2 (
) 2 (
h N Td
h N Td
Ad
× + ×
× − ×
=
: derivation gain
) 2 (
) 2 (
h N Td
Td N K
Bd
× + ×
× × ×
=
Tt
h
A
=
0
: anti-windup gain
Step 2 : Read SV and PV value
PV = adin(ch1)
Step 3: Calculate the proportional term.
P = K
×
(b
×
SV – PV)
Step 4 : Update the derivative term. (initial value of D = 0)
D = As
×
D – Bd
×
(PV – PV_old)
Step 5 : Calculate the MV. (initial value of I = 0)
MV = P + I + D
Step 6 : Check the actuator is saturated or not.
U = sat(MV, U_low, U_high)
Step 7 : Output the MV value to the D/A module
Step 8 : Update the integral term.
I = I + bi
×
(SV – PV) + A0
×
(U – MV)
Step 9 : Update the PV_old value.
PV_old = PV