WEG CFW700 User Manual - page 38
CFW700 | 33
Keypad (HMI) and Basic Programming
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4.2.1.1 Academic PID
The PID controller implemented in CFW700 is the academic type. The equations that characterize
the Academic PID, which is the base of this function algorithm, are presented next.The transfer
function in the Academic PID regulator frequency dominion is:
y(s) = Kp x e(s) x [1 +
1
+ sTd]
sTi
By replacing the integrator by a sum and the derivative by the incremental quotient, one gets
an approximation for the discrete transfer equation (recursive) presented next:
y(k) = y(k-1) + Kp[(1 + Ki.Ta + Kd/Ta).e(k) – (Kd/Ta).e(k-1)]
Being:
y(k): current PID output, can vary from 0.0 to 100.0 %;
y(k-1): PID previous output;
Kp (Proportional gain): Kp = P1020;
Ki (Integral gain): Ki = P1021 x 100 = [1/Ti x 100];
Kd (Differential gain): Kd = P1022 x 100 = [Td x 100];
Ta = 0.05sec (PID regulator sampling time);
e(k): current error [SP*(k) – X(k)];
e(k-1): previous error [SP*(k-1) – X(k-1)];
SP*: reference, can vary from 0.0 to 100.0 %;
X: process variable (or feedback), read through one of the analog inputs (AIx), can vary from
0.0 to 100.0 %.
The parameters related to this application are:
P1010 – Version of the PID Regulator Application
Adjustable
Range:
0.00 to 10.00
Factory
Setting:
-
Properties:
ro
Access Groups
via HMI:
SPLC
Description:
Read only parameter that presents the software version of the PID regulator application
developed for the SoftPLC function of the CFW700.
P1011 – PID Setpoint
Adjustable
Range:
0.0 to 3000.0
Factory
Setting:
-
Properties:
ro
Access Groups
via HMI:
SPLC
Description:
Read only parameter that presents, in the wxy.z form without engineering unit, the feedback
value of the PID regulator according to the scale defined at P1018.