This paper investigates the problem of robust guidance law design for multiple unmanned aerial vehicles to achieve desired formation pattern for standoff tracking of an unknown ground moving target. The proposed guidance law consists of two main parts: relative range regulation and space angle control. For the first mission, a novel control law is proposed to regulate the relative distance between the unmanned aerial vehicle and the ground moving target to zero asymptotically based on adaptive sliding mode control approach. Considering the discontinuous property of the sign function, which is often used in traditional sliding mode control and will result in high-frequency chattering in the control channel, the proposed controller adopts the continuous saturation function for chattering elimination. Besides the continuous property, convergence to the origin asymptotically can be guaranteed theoretically with the proposed controller, which is quite different from traditional boundary layer technique, where only bounded motion around the sliding manifold can be ensured. For asymptotic stability, it is only required that the lumped uncertainty is bounded, but the upper bound may be unknown by virtue of the designed adaptive methodology. For space angle control, a new multiple leader–follower information architecture is introduced and an acceleration command is then derived for each unmanned aerial vehicle to space them about the loiter circle defined by the first controller. Simulation results with different conditions clearly demonstrate the superiority of the proposed formulation.
A review on fault-tolerant cooperative control of multiple unmanned aerial vehicles
