Direct adaptive actuator failure compensation control: a tutorial

A resilient control system is expected to have the capacity to restore the desired system stability and tracking performance in the presence of uncertain system faults such as actuator failures. While redundant actuators are used for actuator failure accommodation, uncertain actuator failures, whose failure time, pattern, and values may be unknown, can bring new challenges to feedback control design as such uncertain failures can introduce large structural, parametric, and actuation uncertainties. Two technical issues are associated with using redundant actuators: how redundant actuators should be coordinated for effective failure compensation control, and how a feedback control law should be adaptively designed to compensate uncertain actuator failures. In this paper, we present a tutorial on direct adaptive failure compensation-based solutions to these issues for different types of control systems: state tracking using state feedback, output tracking using state feedback or output feedback, for linear, non-linear, and multi-input multi-output systems. We give an overview on such adaptive actuator failure compensation designs which have special capacities to effectively use actuation redundancy to handle uncertain actuator failures, using either direct or indirect adaptive control approaches for direct adaptive actuator failure compensation without explicit failure detection, for fast and effective failure accommodation.