Output feedback stabilization of uncertain nonholonomic systems with external disturbances via active disturbance...

This paper investigates a class of nonholonomic systems with multifarious uncertainties including unmodeled dynamics, linear or nonlinear parameterization and unknown external disturbances. The objective is to deal with all uncertainties in a unified framework and simultaneously realize the global stabilization of the nonholonomic system. In terms of the nonholonomic constraints, a concise switching strategy is employed for stabilizing the whole system. Active disturbance rejection control (ADRC) is designed for an uncertain lower-triangular subsystem which is transformed from the nonholonomic system by using an input-state scaling technique. All system uncertainties are involved as the equivalent total disturbance which can be estimated by extended state observer (ESO) and compensated for by a feedback control input. Closed-loop performance analysis clarifies that the uncertain subsystem can be stabilized and the observation errors can be regulated to zero by tuning the bandwidth of the ESO. Simulations on a bilinear model illustrate the effectiveness of the proposed method.