Full Attitude Control of an Efficient Quadrotor Tail-sitter VTOL UAV with Flexible Modes
For UAV control engineers, this work provides a practical method to compensate for flexible modes in tail-sitter VTOLs without control surfaces, though it is incremental in applying known frequency-domain techniques to a specific platform.
The paper presents a full attitude control system for a quadrotor tail-sitter VTOL UAV with flexible modes, achieving superior tracking performance and robustness by optimizing controller parameters and filters based on frequency response models. Tests in hovering, forward accelerating, and decelerating flights validated the system.
In this paper, we present a full attitude control of an efficient quadrotor tail-sitter VTOL UAV with flexible modes. This control system is working in all flight modes without any control surfaces but motor differential thrusts. This paper concentrates on the design of the attitude controller and the altitude controller. For the attitude control, the controller's parameters and filters are optimized based on the frequency response model which is identified from the sweep experiment. As a result, the effect of system flexible modes is easily compensated in frequency-domain by using a notch filter, and the resulting attitude loop shows superior tracking performance and robustness. In the coordinated flight condition, the altitude controller is structured as the feedforward-feedback parallel controller. The feedforward thrust command is calculated based on the current speed and the pitch angle. Tests in hovering, forward accelerating and forward decelerating flights have been conducted to verify the proposed control system.