The following is the structure diagram of the PI1 controller:
The
PI1 control structure is displayed in the
Structure diagram. Setting parameters for the function block takes place first of all for the elemental
PI parameters: the proportional action coefficient
GAIN and reset time
TI.
The limits YMAX and YMIN limit the output within the prescribed range. Therefore YMIN ≤ Y ≤ YMAX.
The markers QMAX and QMIN signal that the limits have been reached or the output signal is being limited.
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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
Should limiting of the manipulated variable take place, the anti-windup reset should ensure that the integral component "cannot go berserk". The anti-windup measure is only implemented if the I component of the controller is not disabled. Anti-windup limits are identical to those for the manipulated variable. The anti-windup-reset measure corrects the I component such that: YMIN - YP ≤ YI ≤ YMAX - YP
