ROBUST CONTROLLER SYNTHESIS FOR SYSTEMS WITH INPUT NONLINEARITIES - ATRADE-OFF BETWEEN GAIN VARIATION AND PARAMETRIC UNCERTAINTY

A feedback control-system design problem involving input nonlinearitie s and structured plant parameter uncertainities is considered. Multiva riable absolute stability theory is merged with the guaranteed cost co ntrol approach to robust stability and performance to obtain a theory of full- and reduced-order robust control design that accounts for inp ut time-varying sector bounded nonlinearities. The principal result is a sufficient condition for characterizing dynamic controllers of a fi xed dimension which are guaranteed to provide robust stability for pla nt parametric variations and absolute stabilization for input nonlinea rities. The proposed framework provides a systematic design trade-off between classical robustness guarantees (i.e., gain and phase margins) versus parametric robustness. Furthermore, the framework is directly applicable to uncertain systems with saturating controls and provides fixed-order dynamic output feedback controllers with guaranteed domain s of attraction. (C) 1998 John Wiley & Sons, Ltd.