Systematic closed-loop design in the presence of input saturations

This contribution distinguishes between two conceptually different windup p henomenons, namely controller and plant windup. Even in the absence of dyna mic controller elements, saturating nonlinearities can trigger undesired os cillations. This effect is obviously due to inappropriate plant states, and is therefore called plant windup. Based on the frequency response of the l inear part, a design aid for plant windup prevention is presented. It facil itates the search for suitable closed-loop dynamics, or for an appropriate additional dynamic network. State and disturbance observers add dynamic ele ments to the compensator, and in the presence of very slow or unstable cont roller modes, the well-known reset windup or integral windup occurs. This e ffect, the controller windup, is related to mismatched controller states. B y feeding the limited plant input signal into the observer it is completely removed, so that the remaining effects of input saturation are solely attr ibutable to plant windup. Various known windup prevention techniques can be explained within the presented framework. (C) 1999 Elsevier Science Ltd. A ll rights reserved.