Nonlinear observer-based adaptive thruster allocation for thruster fault tolerant control of over-actuated UUV

  Objective  To deal with the external time-variance disturbances and possible failure of actuators during the dynamic positioning operation of an unmanned underwater vehicle (UUV), this paper proposes a nonlinear observer-based adaptive allocation strategy to achieve thruster fault tolerance.

  Method  The control scheme is first established by means of the power sliding mode control technique to obtain the dynamic position. Meanwhile, a nonlinear disturbance observer is designed to estimate external disturbances. Then, based on the estimated external disturbance and state deviation sequence under the failure mode, a quadratic programming problem is constructed and solved to obtain the efficiency factor of each thruster, and the thrust distribution matrix is modified to achieve adaptive control allocation under thruster fault tolerance.

  Results  The simulation results show that the UUV control system can effectively estimate external environmental disturbances and the efficiency factor of each thruster. Even if the actuator fails, the UUV can still accomplish its dynamic positioning mission.

  Conclusion  The results of this study show that the proposed adaptive thruster allocation and sliding mode control algorithm is reasonable and can be effectively applied to UUVs under external environmental disturbances and actuator failure.