Robust anti-windup control of SISO systems

This paper provides some perspectives on the robust anti-windup (AW) control problem by focusing on the simplest case of AW compensation for uncertain linear single-input-single-output (SISO) systems. Using Quantitative Feedback Theory (QFT)-style frequency domain analysis, and through numerical examples, it is shown that even for simple systems, certain popular AW techniques may fail to provide robust stability when saturation is encountered. A QFT-based AW method, in which uncertainty is explicitly incorporated into the design procedure, is revised to employ less conservative stability multipliers and employed to overcome these robustness deficiencies. Through a robust AW example the paper highlights: the importance of explicitly designing the AW controller to be robust to system uncertainty; the potential failure in designing for robustness based on only the nominal plant, with IMC AW shown to unstable in one case; and the significant reduction in the problem difficulty that can arise from the use of less conservative saturation multipliers.