Trajectory tracking of a quadrotor with unknown parameters and its fault-tolerant control via sliding mode fault observer

Based on the nonlinear equations of a quadrotor, position tracking with unknown parameters and fault-tolerant control scheme is proposed in this article. First, a multi-loop structure is designed with multiple time-scale analysis to make the system realizable. Then, to achieve the goal of accurate tracking, a sliding mode fault observer is added into each loop to accommodate the effects of all the uncertainties. This controller shows great applicability because of the simple structure. The only information the controller needs to know is the limits of uncertainties. In addition, since the above controller cannot guarantee robustness when the system model is unknown, an online adaptive estimation method is proposed to learn the parameter information. Stability of the overall closed-loop system is analyzed with the Lyapunov stability theory, and output tracks the expected trajectory. The simulation is presented with several situations (including adaptive estimation result test/robust test under parameter uncertainties and high-frequency noise/fault-tolerant ability under actuator faults) to verify the effectiveness and feasibility of the proposed scheme.