A QFT design methodology for neutrally stable plants under input amplitude saturation

A control system design methodology for neutrally stable plants under input amplitude saturation is presented. Based on Horowitz´s (1983) original 3 DOF design and extensions developed in Wu and Jayasuriya (1999, 2000) and Wu (2000), this approach concentrates on neutrally stable, type n ≥ 1, plants. Again, the 3 DOF non-interfering loop structure is used for synthesis, along with the proposed structure of the additional loop transmission around the saturating element to design the third degree of freedom H(s). Robust stability and performance are investigated. The circle criterion, describing function, and non-overshooting conditions are utilized to obtain design constraints. Finally, all these design constraints are expressed in frequency domain bounds and synthesis follows from loop shaping methods such as QFT.