Velocity-constrained distributed formation tracking of fixed-wing UAVs with multiple leaders

This paper addresses the safety-critical formation tracking of fixed-wing unmanned aerial vehicles, where both the velocity constraint and multiple leaders are taken into consideration. A hierarchical control strategy, consisting of a distributed observer and a formation controller, is elaborately constructed to achieve the desired configuration with the velocity in a safe range. First, a novel distributed observer is designed to estimate the formation error, which promises the practical fixed-time convergence of the estimation error despite unknown inputs of leaders and disturbances. Then, the velocity constraint is enforced through the forward invariance of a safety set, for which a robust control barrier function is carefully constructed considering the effect of disturbances. Further, a local formation controller is established by embedding the robust control barrier function into quadratic programming. Compared with existing results, the proposed controller is able to achieve the formation configuration while satisfying velocity safety, even in the presence of disturbances. Simulations are conducted to demonstrate the proposed method's capability in guaranteeing velocity constraint and stabilizing formation errors.