Fault- Tolerant Control of a Tethered Aircraft for Airborne Wind Energy

Reliability and fault tolerance are crucial aspects for the industrialization of Airborne Wind Energy (AWE) systems, yet the scientific literature on this topic is still scarce. A study on fault tolerant control of a hybrid rigid-wing/quad- copter tethered aircraft used in AWE is presented. The fault tolerant control structure features a combination of passive measures. The former combine daisy chain control allocation with Internal Model Control (IMC), enabling the system to immediately counteract saturations or faults of one or more actuators. The active measure employs a quantitative model-based fault detection and isolation (FDI) approach to identify a failure in one or more of the discrete control surfaces (rudder, ailerons, elevator). The faulty actuator is then excluded from the control allocation strategy. The FDI approach is based on a residual indicator of the discrepancy between the actual system behavior and the one predicted by a dynamical model fed by the commanded control signals. Simulations of a realistic model of the tethered aircraft show promising performance of the method.