Control barrier function based terrain and path following control of unmanned aerial vehicle considering attitude constraint

Abstract A terrain and path following control scheme is designed for ground detection mission of a fixed-wing unmanned aerial vehicle (UAV) considering the attitude constraint. The attitude of the UAV should be maintained for efficient exploration, leading to the degradation of mission performance. The proposed controller makes the attitude of the UAV remain in a desired range, which alleviates the mission performance degradation. The proposed algorithm consists of the guidance law and the nonlinear flight path controller. The guidance law is designed by combining a terrain-following altitude controller and a horizontal path following controller based on the Lyapunov control scheme. The generated command by the guidance law is used as a reference input to be followed in the flight path controller. The flight path controller is designed considering the attitude constraint. Especially, the roll and pitch angles of the UAV are considered as attitude constraints so that the angles remain within the desired range. To design a flight path controller satisfying the attitude constraint, the control system is decomposed into three feedback loops. State-feedback controllers are designed using the sliding mode control scheme for flight path control in the outermost loop as well as for angular rate control in the inner loop. In the second-outer loop, a quadratic programming (QP)-based controller is designed to control the sideslip angle while satisfying the attitude constraint. The control Lyapunov function is adopted to determine the QP constraint for the sideslip angle control, and the control barrier function is used to obtain the QP constraint for the attitude constraint. Numerical simulation is performed to demonstrate the effectiveness of the proposed algorithm.