Incremental nonlinear dynamic inversion based path-following control for a hybrid quad-plane unmanned aerial vehicle

Hybrid quad-plane unmanned aerial vehicles (UAVs), which combine the advantages of multicopters and fixed-wing UAVs, are gaining increasing attention. However, quad-planes are characterized by complex structures, high nonlinearity, strong coupling, and three flight regimes (hover, transition, and fixed-wing flight), which bring great challenges to the research of their control laws. This article aims to design control laws for a quad-plane in fixed-wing and hover flight regimes based on a robust nonlinear control method, incremental nonlinear dynamic inversion (INDI), so that the quad-plane can follow a given path autonomously. Firstly, a mathematical model of the quad-plane is established on the basis of kinematics and dynamics. Subsequently, cascade control structures are proposed and divided into inner and outer loops. A control law is designed for each control loop based on INDI. To improve the performance of the designed control law, reference models are added to the inner loops to shape the input commands and provide feedforward inputs. Finally, simulation results corroborate the performance and robustness of the proposed control law. Compared with the control law designed by active disturbance rejection control and proportional-integral-derivative control methods, the INDI-based control law is more robust.