Multi-level Thrust Allocation Method Based on Fuzzy Logic for a Remotely Operated Vehicle with Hybrid Propulsion System

For a remotely operated vehicle (ROV) with hybrid propulsion system, a multi-level thrust allocation method based on fuzzy logic is proposed, to combine the advantages of high efficiency and large capacity of electric propulsion system, and the advantage of fast response of hydraulic propulsion system. Firstly, a three-dimensional fuzzy controller is constructed to distribute the increment of the expected longitudinal force. Then, the allocation of the desired longitudinal force is calculated considering the thrust capabilities of the two propulsion systems, and the expected longitudinal force is divided into two parts, corresponding to the two propulsion systems respectively. Finally, the thrust allocation is carried out respectively for the electric propulsion system and the hydraulic propulsion system, and the thrust command for each thruster is obtained. Comparative simulation results show that the allocation proportion of the expected longitudinal force can be adjusted dynamically according to requirements of thrust and states of the propulsion systems, which brings the ROV a good performance in terms of motion ability and operation efficiency. It is verified that the proposed method is more flexible and effective than the pseudo-inverse method.