Improving local anti-windup performance: preliminary results on a two-stage approach

To obtain improved local performance while retaining the property of global stability, this paper proposes a new two-stage approach to anti-windup compensation for systems containing input saturation. The method ensures that (i) if no saturation occurs, then linear operation continues unhindered; (ii) if mild saturation occurs, an aggressive local antiwindup compensator becomes active and; (iii) if severe saturation occurs a globally stabilising anti-windup algorithm enters the fray. A notable feature of the scheme is that, for stable plants, a two-stage compensator will always exist. Another interesting aside, is that simple, possibly ad hoc techniques can be combined to yield a good two-stage compensator which may perform better, locally, than many 'optimal' schemes.