Real time Optimal Allocation for I-AUV with Interacting Thrusters

Energy saving is a relevant issue for battery powered Intervention Autonomous Underwater Vehicles which are designed for both short and long-range mission. The energy consumption of an I-AUV is affected by several effects like hydrodynamics, onboard electronics and thrusters cross-couplings. I-AUVs are usually over-actuated system, thus the actuator's interaction takes relevance and should take part within the energy saving process. In this paper the authors present a study on optimal control allocation that aims at considering the interactions between the propellers of an over actuated vehicle where usually two or more thrusters can interfere each other resulting in reduction of the allocation efficiency. The paper presents the mathematical formulation for interacting propeller considering the wake effect and proposes to dynamically adjust the control allocation matrix in order to obtain a cost effective control allocation without modifying the control layer. The existence of a minimum in the energy consumption during the cruising task in function of the parametric control allocation matrix is proved numerically. Thus a perturbation-based extremum seeking approach is used in order to dynamically adapt the parametric allocation matrix and seek the optimal allocation setpoint without explicit knowledge of the real coupling.