Active Disturbance Rejection Attitude Control for a Quadrotor UAV With Control Input Constraints

External disturbances, model uncertainties and parameter mismatches of a quadrotor unmanned aerial vehicle (UAV) degrade its flight control performance and may even compromise flight safety. Active disturbance rejection control (ADRC) is feasible in a quadrotor UAV. However, various physical, safe and economic constraints are ubiquitous, and unlike the predictive control, the ADRC does not consider constraints in its design. To address this, we propose an ADRC with control input constraints (ADRC-CIC) by incorporating advantages of both the ADRC and the dynamic matrix control (DMC). Its inner loop is a closed-loop ADRC system, and its outer loop is a DMC control loop. A constraint transformation is performed, then the ADRC-CIC can explicitly deal with constraints. If proper parameters are chosen, the inner loop system approximates a linear time-invariant system, and its dynamics is taken as a predictive model. Then, a system, no matter stable or unstable, linear or nonlinear, becomes controllable in the framework of the ADRC-CIC. Theoretical analysis has been conducted. Experimental results of a quadrotor UAV confirm the ADRC-CIC.