Active disturbance rejection controller for small fixed-wing UAVs with model uncertainty

The mathematical model of small fixed-wing UAV is difficult to determine precisely, especially for low-cost UAVs due to the limitation of the body material. Control of small UAVs with model uncertainty is an open problem both in the control community and engineering field. Active disturbance rejection control (ADRC) proposed by Jingqing Han has been shown to be an effective tool in dealing with real world problems of dynamic uncertainties, disturbances, nonlinearities, etc. To increase the robustness of the inner-loop controllers of small fixed-wing UAVs with model uncertainty, three ADRC controllers are designed for roll, pitch and speed control respectively. The subsistent coupling between the decoupled control loops is considered as unmodeled dynamics, which can be estimated and compensated using an extended state observer (ESO). The performance and robustness of the inner-loop attitude controllers are evaluated by numerical simulation as well as actual flight test.