Variable Structure Observers for Nonlinear Interconnected Systems

In this chapter, a variable structure observer is designed for a class of nonlinear large-scale interconnected systems in the presence of uncertainties and nonlinear interconnections. The modern geometric approach is used to explore system structure and a transformation is employed to facilitate the observer design. Based on the Lyapunov direct method, a set of conditions are developed such that the proposed variable structure systems can be used to estimate the states of the original interconnected systems asymptotically. The internal dynamical structure of the isolated nominal subsystems as well as the structure of the uncertainties are employed to reduce conservatism. The bounds on the uncertainties are nonlinear and are employed in the observer design to enhance robustness. A numerical example is presented to illustrate the results and simulation studies show that the proposed approach is effective.