Step by step robust nonlinear PI for attitude stabilisation of a four-rotor mini-aircraft

Based on the Euler angles parameterization, a new approach for the attitude control of a vertical take-off and landing (VTOL) quadrotor aircraft is proposed. It rests on the combination of the backstepping technique and a nonlinear robust PI controller. The integral action gain is nonlinear and based on a switching function that ensures a robust behaviour for the overall control law. One of the strengths of the proposed approach is its robustness with respect to plant parameters uncertainties. The proposed approach has been tested in simulation and shows good performance.