Novel barrier Lyapunov function-based backstepping fault tolerant control system for an ROV with thruster constraints

Abstract

This paper proposes a novel Barrier Lyapunov Function (BLF)-based fault tolerant control system for a work-class Remotely-Operated Vehicle (ROV) with thruster saturation and rate limits. The proposed control system is composed of a fixed-time state and fault observer, and a novel BLF-based backstepping controller. The novel BLF-based controller is introduced to eliminate the sensitivity of conventional BLF-based algorithms to rate limitations of the thrusters. In addition, it helps to improve the performance during initial transients and provides faster response to fault and failures. The observer combines the dynamics of the ROV with the dynamics of the thruster system. This combination facilitates estimation of thruster faults and failures independently of the system uncertainties, so highly improved performance is expected compared to conventional extended-state observers. To account for thruster constraints and provide fault tolerance, control allocation is utilized. Stability analysis is performed for the observer and controller, and it is shown that the state estimation error is fixed-time convergent, the fault estimation unit is bounded-input bounded-output stable, and the controller is exponentially stable. Simulations are carried out and comparisons are made with several asymptotic and finite-time BLF-based control systems. The simulations confirm the superior performance of the proposed control system.