Stability and robustness for discrete-time systems with control signal saturation

All practical control systems exhibit control signal saturation. The effect that this saturation has on the control system performance, especially sta bility and robustness, can be significant and must be understood at the con troller design stage. This paper presents conditions for global asymptotic stability and measures of stability robustness for such systems. These are demonstrated through simulation examples, and it is shown how an understand ing of the stability conditions can inform the controller design process. T he off-axis circle criterion is used as the basis for a sufficient conditio n for stability, and it is argued that this is not overly restrictive in pr actice. The derivations are carried out in discrete time, and servo-system control is envisaged as an important application area for the techniques; h owever, the results are applicable more widely.