Design of finite-time active fault tolerant control system with real-time fault estimation for a remotely operated vehicle

In this paper, a new approach is introduced for active fault tolerant control system of an underwater vehicle with unknown dynamics in the presence of thruster system faults and constraints. For this, a finite-time observer is proposed to estimate unknown system dynamics and the faults and failures of the thruster system simultaneously. In the observer, a novel unit based on acceleration feedforward is introduced into conventional extended-state observer so that real-time estimation of fault can be obtained regardless of uncertainties and disturbances. Stability analyses are carried out for the observer and it is proved that system states and uncertainties can be estimated in finite time and fault estimation error is proved to be globally uniformly ultimately bounded. In order to actively accommodate thruster system faults and failures, and to take saturation and rate limits into account, control allocation is utilized. To outline the advantages of the proposed control system, comparisons are made with previous works. The results show that the proposed observer has effectively estimated thruster system faults and failures. It is also shown that the post-failure/-fault behavior of the vehicle has significantly improved and despite keeping the position more accurately, the performance of the thruster system has considerably improved.