Uniform Passive Fault-Tolerant Control of a Quadcopter with One, Two, or Three Rotor Failure (2211.12972v2)

Abstract: This study proposes a uniform passive fault-tolerant control (FTC) method for a quadcopter that does not rely on fault information subject to one, two adjacent, two opposite, or three rotors failure. The uniform control implies that the passive FTC is able to cover the condition from quadcopter fault-free to rotor failure without controller switching. To achieve the purpose of the passive FTC, the rotors' fault is modeled as a disturbance acting on the virtual control of the quadcopter system. The disturbance estimate is used directly for the passive FTC with rotor failure. To avoid controller switching between normal control and FTC, a dynamic control allocation is used. In addition, the closed-loop stability has been analyzed and a virtual control feedback is adopted to achieve the passive FTC for the quadcopter with two and three rotor failure. To validate the proposed uniform passive FTC method, outdoor experiments are performed for the first time, which have demonstrated that the hovering quadcopter is able to recover from one rotor failure by the proposed controller and continue to fly even if two adjacent, two opposite, or three rotors fail, without any rotor fault information and controller switching.

• The paper presents a passive fault-tolerant control method that models rotor failures as disturbances to maintain stability across varying fault scenarios.
• It employs dynamic control allocation to adapt the same control strategy for single, double, or triple rotor failures without redesign.
• Experimental validation shows robust hovering and accurate path following even when up to three rotors fail, enhancing UAV reliability.

Overview of Uniform Passive Fault-Tolerant Control of a Quadcopter with Rotor Failures

This paper presents a uniform passive fault-tolerant control (FTC) method for quadcopters that is capable of addressing rotor failures without the requirement of rotor fault information or controller switching. This research focuses on enhancing the reliability and safety of quadcopters, particularly in scenarios where one, two, or three rotors may fail, by employing a method that integrates disturbance modeling, dynamic control allocation, and stability analysis.

Key Contributions and Methods

The research stands out for its ability to manage fault conditions uniformly for different rotor failure scenarios: one rotor, two adjacent rotors, two opposite rotors, and three rotor failures. The central feature of the proposed method is its passive FTC approach, which addresses the rotor failure by modeling it as a disturbance in the virtual control framework, allowing the control system to maintain stability across all fault conditions without necessitating real-time fault detection and diagnosis (FDD) or switching between controllers.

1. Disturbance Model: The rotor fault is modeled as a lumped disturbance acting on the system. This disturbance is accounted for using an estimation approach that dynamically compensates for the faults, thereby eliminating the need for precise fault information about the rotor failures.
2. Dynamic Control Allocation: The control allocation technique utilized ensures that the system adapts to different rotor faults seamlessly, allowing the same control strategy to be applied across various failure conditions without any redesign or parameter adjustment.
3. Stability Analysis and Control Strategy: The paper offers a theoretical framework for the stability of the proposed FTC method. It presents an analysis ensuring that the closed-loop system remains stable despite the presence of faults. The controller is enhanced through a virtual control feedback mechanism that improves the response time and resilience of the quadcopter under failure conditions.

Experimental Validation and Results

The research findings have been validated through extensive outdoor experiments, featuring scenarios with various rotor failures while recovering from states where up to three rotors have failed. The experiments demonstrate a stable hovering capability and ability to follow predetermined navigation paths even when multiple rotors are inoperable.

Implications and Future Directions

This paper provides significant implications for the design of reliable flight control systems within the domain of unmanned aerial vehicles (UAVs). By eliminating the dependency on FDD systems and controller switching mechanisms, the passive FTC framework reduces computational burdens and potential delays in failure response times.

This method's practical application extends beyond quadcopters, with potential adaptations suitable for other types of UAVs, such as hexacopters, which could benefit from increased redundancy and fault-tolerance capabilities. Future research could explore further integration with sensor fusion technologies and machine learning for even more robust fault diagnostics and automated tuning of controllers in response to varying flight dynamics and operational environments. Moreover, expanding the scope to include networked multi-agent UAV systems could pave the way for resilient swarm operations in complex indoor and outdoor environments.