Block diagram of the PPI cascade controller
Setting parameters for the function block takes place firstly through the proportional correction value (gain1) and the offset for the output of the p-controller (OFF).
Subsequently setting parameters for the PI controller takes place through the proportional correction value gain2 and the reset time ti.
The I component can be disabled by setting ti = 0.
The limits ymax and ymin limit the output within the prescribed range.
The outputs qmax and qmin signal that the output has reached a limit, and thus been capped.
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qmax = 1, if Y ≥ ymax
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qmin = 1, if Y ≤ ymin
Manipulated variable limiting
After summation of the components manipulated variable limiting takes place, so that: ymin ≤ Y ≤ ymax
Anti-windup reset (PI controller)
If manipulated variable limiting takes place, the anti-windup reset should make sure that the integral component of the master controller "is not able to exceed all limits". The anti-windup measure can only be used if the I component of the sub-controller is not disabled.
The anti-windup reset takes place if:
Y ≥ ymax or Y ≤ ymin
In this case, it is:
YI = Y - YP
