Nonlinear attitude control of tiltrotor aircraft based on active disturbance rejection sliding mode method

Tiltrotor aircraft is a kind of aircraft which can fly as a fixed wing aircraft or a helicopter by tilting its two rotors' mast angle, which means it has both the advantages of helicopter and fixed wing aircraft. To control it well, a nonlinear mathematical model based on Pitt-Peters dynamic inflow theory is established. Since traditional control method based on linearized model needs extensive gain scheduling with the mast angle and flight state, a novel control method named active disturbance rejection sliding mode controller (ADRSMC) based on active disturbance rejection controller (ADRC) and sliding mode controller (SMC) is designed. First of all, a tracking differentiator (TD) is utilized to get the command of attitude and angular rate. Because the disturbance of the novel model includes the model error and coupling between different channels, a novel sliding mode extended state observer (SMESO) base on sliding mode theory is developed to estimate the disturbance of model. After that, a novel control law based on dynamic surface control theory is developed. And the stability of ADRSMC is proved. The parameters of ADRSMC are not changed during the whole process of simulation. Simulation results in various flight conditions show that ADRSMC is feasible and parameters are available in a wide range.