Saturation in Engineering Simulation

The wind-up effect is a phenomenon known mostly from implementing PI(D) controllers in real operation when saturation of the manipulated variable may occur and cause worse control results. Nowadays many publications exist on this topic where several anti wind-up mechanisms are presented and discussed. However, the wind-up phenomenon, i.e. the problem of continued integration after the output has become limited (saturated), is a problem appearing not only in connection with numerically calculated control actions of digital controllers, but also in computer models of controlled plants. In this field, existence of the wind-up effect is somehow missed. Results and conclusions obtained by such inaccurate simulation may be misleading. Surprisingly, occurrence of this situation is not so rare, because use of amplitude limiting blocks in simulation is considered to be the only necessary precaution. In education of many control engineers, information about wind-up effect in simulation is not sufficiently pointed out. In models of higher than first order, the same approach as the one used the filed of PI(D) controllers is not always correct. The publications focused on the solutions for this case seem to be rare, if any exist. This paper presents one possible approach to wind-up and anti wind-up mechanism in modeling and simulations.