Research On Multi-UUV Formation Control With Time Delay

The depth control of multi-UUV formation is the basis for completing missions such as Marine environment construction,submarine pipeline inspection and military reconnaissance.At present,nonlinearity,model uncertainty and underactuation are common problems in UUV,as well as the limitations of complex Marine environment and underwater acoustic communication,which increase the difficulty of UUV formation control at fixed depth.In recent years,UUV has gradually realized modularization and intelligentization,which makes the Network Control System(NCS)widely used in the internal Control structure of UUV.The Network Control System improves the stability of the internal communication of the vehicle,but at the same time produces communication delay.Aiming at the time delay in UUV formation communication topology and the state delay in UUV internal network system,a more stable and efficient fixed-depth formation controller is designed,taking into account the influence of ocean current and model uncertainty on the controller.Based on the analysis and research on the underactuated UUV fixed-depth formation with time delay,it is divided into three parts: depth control,path tracking control and formation coordination control.Depth controller is designed by sliding mode variable structure method,path tracking controller is designed by reverse step method,and formation coordination controller is designed based on consistency theory.Firstly,the hardware architecture based on NCS and layered control in underactuated UUV are described in detail.Secondly,the 5-degree-of-freedom model of underactuated UUV is established(rolling is not considered).The 5-degree-of-freedom model is decoupled into a vertical plane model and a horizontal plane model,and the two models are simulated and verified.Secondly,state delay and model uncertainty are introduced on the basis of underactuated UUV vertical plane model to establish a new mathematical model.The integrated sliding mode surface and sliding mode equivalent control law with state delay are designed based on the state observer model,so that the state points are in the ideal sliding mode at the beginning,without any influence of approaching motion and external interference,and completely in line with the idea of global robust control.For the discontinuous part of the system,the sliding mode switching control law is designed based on adaptive parameter estimation to keep the state points sliding on the integral sliding mode surface.Compared with the traditional sliding mode controller,the proposed controller has almost no output chattering and higher control accuracy.Furthermore,due to the influence of complex environment and the limitation of underwater acoustic communication bandwidth,there must be time delay in UUV formation communication network.The communication time delay of any two UUVs in the topology is unified to simplify the controller design.The state at time t is estimated iteratively according to the state at time t-τ,so the time-delay system is transformed into a non-time-delay system.The design process of parameters is given,and the stability of the formation control system is proved.Finally,the effectiveness of the designed formation coordination controller is verified by simulation.Finally,considering the influence of ocean current and unmodeled part on formation coordination control,a current observer is designed for the ocean current.An adaptive method is adopted to correct the unmodeled part of the system in real time,and a tracking controller is designed based on the reverse step method.Considering the time-delay problem of underwater acoustic communication,the expected velocity of each UUV is controlled according to the expected arc length difference of each node’s expected path point,that is,the output of the formation controller is used as the input of the tracking controller to realize the formation coordination control,and the stability is proved.Finally,the effectiveness of formation control is verified by simulation.