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Aerial slung-load position tracking under unknown wind forces
P. Pereira, J. Cortés, D. V. Dimarogonas
IEEE Transactions on Automatic Control 66 (9) (2021), 3952-3968

Abstract

We propose a dynamic controller for position tracking of a point-mass load attached to an aerial vehicle by means of a cable. Both the load and the aerial vehicle are subject to unknown wind forces. We model the dynamics of the slung-load system and put it into canonical form, i.e., a form which is independent of the system's physical parameters. Following a backstepping strategy, we design a dynamic control law for the canonical system that contains four estimators, since each of the two wind disturbances has two separate effects: an effect on the linear acceleration and another on the angular acceleration. Loosely speaking, the difference between the wind forces is an input-additive disturbance, while the wind force on the load is not, which makes removing the wind force on the load non-trivial. We identify conditions on the desired position trajectory and on the wind on the load which guarantee that a well-defined equilibrium trajectory exists. The designed controller guarantees simultaneously that (i) the latter trajectory is asymptotically tracked and (ii) the cable remains taut, provided that the system is initialized in a suitable set. Simulations illustrate our results.

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