11.2. Antireset Windup

Reset (Integral) Windup

The phenomenon of reset windup occurs when a controller with integral action operates with the manipulated variable at a constraint for a period of time. When the manipulated input hits the constraint, the integral term in a PID controller continues to accumulate the error, requesting more and more manipulated variable action; the manipulated input cannot increase, however, since it is already constrained. Owing to this integral windup, the manipulated variable may stay saturated longer than is necessary. A block diagram for a process with manipulated input constraints is shown in Figure 11-1a, where v represents the unconstrained input from the controller, while u represents the actual constrained ...

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