Hierarchical fault-tolerant formation control for unmanned helicopters based on fully-actuated system approach

To address the problem that the existing active fault-tolerant control methods for unmanned helicopters fail to consider the influence of fault estimation errors on the formation control accuracy, the game relationship between fault estimation errors and auxiliary controllers is established. By integrating zero-sum differential game theory and the full-actuated system approach, a hierarchical fault-tolerant formation control strategy is developed. Firstly, virtual control variables are introduced, and the high-order fully actuated system model of the unmanned helicopter with actuator fault is established, including the position outer-loop and attitude inner-loop high-order fully actuated subsystems. Subsequently, an adaptive fault estimator is designed to estimate the fault of unmanned helicopter effectively. Then, combining the fault estimation information and the fully actuated system approach, the position and attitude fault-tolerant controllers are designed in a hierarchical manner for the inner and outer loops of the unmanned helicopter, ensuring that the system state satisfies the formation control objective under faults. Furthermore, a zero-sum differential game model between auxiliary controller and fault estimation error is introduced, and the approximate optimal solution is obtained by adaptive dynamic programming algorithm under the dynamic event-triggered mechanism, effectively compensating for the impact of the fault estimation error on the formation performance at minimum cost. Finally, the effectiveness and superiority of the proposed control strategy are demonstrated by simulation experiments. The results show that, under fault conditions, the proposed control strategy can further improve the formation performance of the unmanned helicopter system.