| Robust design of single-input single-output (SISO) uncertain linear time invariant (LTI) systems subject to input saturation is studied. A frequency domain design methodology implemented using QFT procedures is proposed for single saturation (amplitude or rate) via a 3DOF (degrees-of-freedom) control loop structure, and for both rate and amplitude saturation via a 4DOF control loop structure.; In the case of only amplitude or rate saturation, introduction of a 3rd DOF improves the system nonlinear responses significantly. Frequency domain design constraints on the 3rd DOF are derived for three sub-classes of type n ≥ 1 plants: stable plants, neutrally stable plants, and unstable plants, respectively. However, identical results obtained implies the direct applicability of this methodology to the general class of type n ≥ 1 plants. Under saturation, both robust stability and robust performance of the linear design are preserved substantially through proposed strategies.; In the case of having both rate and amplitude saturation, a design methodology utilizing 4DOFs in the control loop is proposed. It is a natural integration of individual designs for amplitude and rate saturation. It applies to the general class of type n ≥ 1 plants. Again, overall system behaviours under saturation are greatly enhanced using the proposed methodology. |
