Research and application of nonlinear control techniques for quadrotor UAV

Quadrotor UAV is a classical multi-input and multi-output system, which is nonlinear, complicated and dynamically unstable. Quadrotor dynamics is considered to consist of translation and rotational subsystems. Nonlinear control strategies that include backstepping method and sliding mode control (SMC) for both translational and rotational dynamics are implemented for the quadrotor. The stability of the control design is ensured by the Lyapunov global stability theorem. Additionally, in order to improve the dynamic response and avoid the violation of the control input constraints, the piecewise differentiable input is applied instead of the step input for the control of the rotational subsystem. The performance of the nonlinear control algorithm is evaluated by simulation, whose results validate the effectiveness of the designed control strategies for the quadrotor near quasi stationary (hover or near hover) flight. Finally, a comparison between backstepping and the slide mode is carried out briefly to highlight the respective characteristics.