Three-Dimensional Composite Approach Angle Constrained Guidance Law with Actuator Lag Consideration

This paper considers the problem of unmanned aerial vehicle (UAV) aerial collision net recovery in a three-dimensional non-decoupling environment and approach angle constraint. A robust control-observer framework-based guidance law was designed via the nonsingular fast terminal sliding mode control (NFTSMC) technique and adaptive sliding mode disturbance observer (ASMDO). To estimate the disturbance of the guidance system in finite time, an ASMDO is presented in which the parameters are autonomously adjustable according to the estimation error. The proposed control implementation uses the nonsingular fast terminal sliding mode (NFTSM) technique to drive the line-of-sight (LOS) angle error and LOS angular rate fast convergence under model coupling and external disturbance. Furthermore, regarding the actuator of UAV with second-order dynamic, a backstepping guidance law to compensate for actuator dynamics is proposed with the aid of a finite-time converged differentiator, which can estimate directly the derivative of the virtual control law and guarantee the finite-time convergent characteristic of the partially integrated guidance and control system. Simulation studies and comparisons verified the efficiency of the proposed guidance law in the presence of a complex disturbance lump.