Singularity Free Dynamic Control Allocation for Tilt-Rotor Multirotor Unmanned Aerial Vehicles.

Tilt-rotor multi rotor unmanned aerial vehicles (UAV s) are a developing field of research due to their advantages of flexible flight capability and pose-omnidirectionality. Although numerous control allocation algorithms have been presented with relatively good reliability, some singularity configurations of tilt-rotor UAV can cause the algorithm to fail in generating a stable solution. This paper proposes a singularity-free dynamic control allocation algorithm that improves the stability of tilt-rotor multi rotor UAV s in 6 degrees of freedom (DOFs). The control allocation is formulated as a constrained optimization problem by introducing the inequality constraints derived from singular configurations. The barrier function is embedded into the objective function for constraints enforcement. The Lagrange function is then used to form the unconstrained optimization objective function. A Lyapunov-like function is proven to be negative semidefinite, time invariant and bounded. Through Barbalat's lemma, the algorithm is Uniformly Globally Stable. Simulation results obtained from trajectory tracking at singularities of the tilt-rotor multi rotor UAVs in 6 DOFs demonstrate validity of the proposed dynamic control allocation approach.