Design of sliding mode controllers for quadrotor vehicles via flatness-based feedback and feedforward linearization strategies

Unmanned Aerial Vehicles (UAVs) have to operate in complex environments, characterized by disturbances of different nature that affect the system performance. Moreover, system dynamics can be altered by unavoidable modeling uncertainties, that can further decrease the control performance. This motivates the introduction of robust control strategies and, among them, Sliding Mode Control (SMC) represents a viable solution, provided that the UAV model is led back to a normal form, suitable for control design purposes. This paper investigates two flatness-based linearization approaches, a feedback and a feedforward one, that transform the nonlinear and coupled quadrotor model into a canonical form eligible to design a trajectory tracking controller based on a battery of Higher-Order Sliding Mode (HOSM) regulators. Simulation results, based on a realistic model of a quadrotor, are presented to assess the performance of the proposed control system.