New results in the global stabilization of nonlinear systems via measurement feedback with application to nonholonomic systems

We study the problem of globally stabilizing through smooth time-varying measurement feedback a wide class of time-varying uncertain nonlinear systems, consisting of a linear nominal time-varying system perturbed by nonlinear terms, model uncertainties and disturbances. The nominal time-varying system is both controllable and observable. Both the uncertainties and nonlinearities are supposed to have a lower triangular structure. We propose a step-by step design, based on splitting the system into n one-dimensional interconnected systems Σ_j, j=1,...,n; assuming that for each disconnected system Σ_j there exists a smooth time-varying measurement feedback stabilizing controller C_j which achieves for the closed-loop system Σ_j oC_j, j=1,..., n, some stability properties, we give conditions under which the interconnection of Σ_j oC_j, j=1,..., n, maintains the same stability properties of the disconnected systems. In general, uniform global asymptotic (not exponential) stability can be obtained. We apply these results to nonholonomic systems with uncertainties in lower triangular form