Controller and plant windup prevention in MIMO loops with input saturation

For SISO control loops with input saturation, there is a systematic two stage windup prevention scheme, namely controller windup prevention by an appropriate realization of the compensator, and plant windup prevention either by a modification of the controlled plant dynamics or by the introduction of an additional dynamic network. The observer technique for controller windup prevention can also be applied to MIMO systems, whereas the phase criterion, indicating the danger of oscillatory plant windup, only exists for open loop stable SISO plants so far. Besides oscillatory plant windup, input saturation can give rise to a second kind of plant windup in MIMO loops, namely deadlock, where all or some of the plant inputs stay saturated permanently. In this paper, a MIMO version of the phase criterion is presented, which for stable plants allows a systematic plant windup detection and removal as in the SISO case. Also, an additional dynamic MIMO network is introduced, so that the two stage windup prevention scheme now becomes feasible for MIMO loops too. A simple MIMO example demonstrates the effects.