Fixed-time control of underwater unmanned vehicle formations: a cooperative strategy based on bipolar homogeneous integral sliding mode

This paper presents a fixed-time formation control method for underwater unmanned vehicles (UUVs) based on dual-level homogeneous integral sliding mode control, tackling challenges from unknown disturbances and acoustic communication constraints. A distributed fixed-time observer is first developed to overcome communication limitations, allowing each follower to estimate the leader's position and velocity within fixed time using its own state and locally available neighbor information. Then, to handle unknown external disturbances, a fixed-time formation controller is designed by combining dual-level homogeneous theory with integral sliding mode control. The proposed controller guarantees that followers converge to the desired formation in fixed time while compensating for disturbances, thus improving system robustness. Simulation results confirm the effectiveness of the method.