Low Altitude Control of the VTOL UAV Tolerant to Ground Effect and Actuator Failures

This paper proposes a novel robust control law to stabilise the altitude of a vertical take-off and landing (VTOL) aircraft subject to ground effect and thrust faults. The VTOL UAV dynamics consider external disturbances, unmodeled dynamics, ground effect, and time-varying additive actuator faults. We perform extensive numerical simulations at altitudes between 0.05-0.2 m for a small Bitcraze Crazyflie 2.0 multirotor through three ground effect models. The VTOL UAV operates at low altitudes close to the ground in a hover state. Numerical simulations show that the control algorithm is precise and robust enough to stabilise the aircraft at low altitudes without including a ground effect compensator. A new form of active disturbance rejection control approach is proposed to guarantee asymptotic stability with endogenous and exogenous disturbances.