Lateral guidance and control of UAVs using second-order sliding modes

An innovative sliding mode based partially integrated lateral guidance and control scheme for UAVs is proposed in this paper. Guidance and control framework based on second order sliding modes is presented to solve the problem of two dimensional path-following. The overall closed-loop system generally consists of an inner control (designed considering system dynamics) and outer guidance (designed considering system kinematics) loop configuration. The main contribution of the technique presented here is the partial integration of the two loops i.e., a guidance and control system via series interconnection of two stable sliding manifolds. In the outer guidance loop, the proposed guidance scheme relies on a nonlinear switching surface with the real twisting algorithm derived at the kinematic level, generating roll error commands. The autopilot based on the super-twisting algorithm using a linear sliding surface forms the inner loop. Proof of existence of the 2-sliding mode, control boundedness and stability of the closed-loop, i.e., the overall guidance and control path-following system with the UAV kinematics and autopilot dynamics, is given. The proposed guidance and control system performance is verified via extensive flight tests of a scaled YAK-54 UAV. Flight results validate the proposed framework for guidance and control design.