Switching Angular Velocity Observer for Rigid-Body Attitude Stabilization and Tracking Control

This paper provides a new switching angular velocity observer formulation to the classical problem of rigid-body attitude tracking control in the absence of angular rate measurements. Exponential convergence of the angular velocity state estimation errors is proven using a novel error signal definition through the use of this switching-type observer. The observer synthesis and convergence properties are independent of controller design. The switching ensures C-0 continuity for all the estimated states. Further, the maximum number of switches required by the observer is shown to be finite and that zeno-type behavior cannot occur. A "separation-property" type result for the attitude tracking problem is established, wherein a proportional-derivative controller uses angular velocity estimates from the proposed switching observer in the absence of actual angular rate measurements, while ensuring almost global asymptotic stability for the overall closed-loop tracking error dynamics. The separation property is also proven to hold when a gyroscopic nonlinear compensation term is added to the proportional-derivative controller.