A new QFT design methodology for feedback systems under input saturation

Presented in this paper is a design methodology for robust stability and ro bust performance for a large class of plants subject to an input saturation nonlinearity. Based on Horowitz's 3-DOF linear design method, a more gener al form for the additional loop transmission around the saturating element is proposed to design the third degree of freedom H(s), for Type n plants, n greater than or equal to1. Robust stability is established with the circl e criterion and the describing function technique, and robust performance i s improved by imposing nonovershooting conditions. All stability and perfor mance requirements are then transferred into frequency domain design bounds which are easily obtained using QFT design techniques: This procedure appl ies to all SISO, Type n, stable plants with uncertainties (parametric or no nparametric), and to marginally stable and conditionally stable plants as w ell.