Observer-based anti-windup compensator design for nonlinear systems

Abstract

This paper presents a method for observer-based nonlinear anti-windup compensator (AWC) design using decoupled architecture for the class of nonlinear systems under input saturation by considering the unavailability of state variables. Novel observer-based nonlinear decoupled and equivalent decoupled anti-windup compensator architectures are proposed for the class of nonlinear systems with input saturation and unmeasured states. The designed constraints are formulated by utilizing Lyapunov function, L2 gain reduction, global sector condition and Lipschitz inequality. Linear matrix inequality (LMI) based conditions are derived for simultaneous design of dynamic nonlinear anti-windup compensator and the state observer gain. Global design of dynamic nonlinear anti-windup compensator and observer gain is provided in order to ensure global exponential L2 stability of the closed-loop system. Furthermore, anti-windup compensation constraints using local exponential L2 stability are also provided to ensure regional closed-loop stability and performance. In contrast to the conventional dynamic AWC schemes for nonlinear systems, the proposed approach can be employed when states of a system are not measurable. Numerical example of the nonlinear DC motor under input saturation is considered to demonstrate effectively of the proposed technique.