Chapter 7 Usage of Various Functions
7-
ౌ
e
Ti
K
dt
dI
= e = (SV – PV) : deviation value
The digitized formula is as following;
)(
)()1(
ne
Ti
K
h
nInI
=
−+
h : sampling period
)()()1( ne
Ti
Kh
nInI +=+
c) D control
The continuous formula of derivative term is as following;
dt
dy
KTdDD
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
)( −−
+
−−
+
−
= nyny
hNTd
KTdN
nD
hNTd
hNTd
nD
d) 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
KBi ×=
: integral gain
)2(
)2(
hNTd
hNTd
Ad
×+×
×−×
=
: derivation gain
)2(
)2(
hNTd
TdNK
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
3) Instruction and parameter setting
For the PID operation of MK80S, following 2 instruction are included in the KGLWIN software. (version 2.0 or later)
No. Name Description
1 PID8 Perform the PID operation
2 PID8AT Perform the auto tuning operation
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