Research On Singular Perturbation Control For Path Following Of Underactuated AUVs

Land resources are being depleted and therefore fail to match the demand of human activities.So that,the exploitation of marine resources has become an inevitable choice for human society to realize sustainable development.As is known,the autonomous underwater vehicle(AUV)plays an important role in ocean exploration and exploitation,meeting the needs of economic,military and scientific activities.Certainly,effective motion control is essential for AUVs to perform the underwater mission safely.It is therefore a great significance in theory and engineering to research on the path following control.Owing to a variety of objective factors,the linear control techniques are commonly used in practical cases.But they usually suffer from small domains of attraction and being sensitive to perturbations and so on,and thus have been unable to satisfy the increased requirement of control performance.To this end,a wide range of different nonlinear control techniques have been studied.However,they usually yield relatively complicated controllers which may be prohibitive in the real world.Moreover,with the growth of complexity of motion control,how to reduce the difficulty and complexity of control design is also a research issue.Hence,this essay will discuss the path following control problem of underactuated AUVs based on the singular perturbation theory,so as to reduce the complexity of control design and develop nonlinear path following controllers which should be simple,easy to implement in reality and also meet the requirement of control performance.More details about the research are as follows:1.Regarding the bottom following control problem for underactuated AUVs,the time scale separation caused by different rates of numerous variables is first exploited via a singular perturbation model formulation,using the concept of the speeds of state variable.On the basis of that,a time scale decomposition method is applied to decompose the full system into two lower order subsystems with different time scales.Then,the control strategies are designed in each subsystem independently,leading to a bottom following control law which is compact and uncomplicated to implement in practice.And the sufficient condition of asymptotically stability for the resultant close-loop system is obtained by calculating the derivative of the composite Lyapunov function along the trajectory of full system.Moreover,the input-output stability for the resultant close-loop system is also analyzed by using the small-gain theorem.2.Regarding the horizontal path following control problem for underactuated AUVs subject to unknown internal and external disturbances,a novel method for the design of disturbance observer(DO)is first developed,based on the integral control technique and singular perturbation theory.So that,the problem of control system design given unknown disturbances is reduced to a problem of model-based control.And then,the time scale separation caused by different rates of numerous variables is exploited via a singular perturbation model formulation.On the basis of that,a three-time scale singularly perturbed control strategy is proposed,which allows independent design in each time scale,leading to a reduction of control complexity and a relatively simple control law.The asymptotically stability for closed-loop system is performed by constructing a composite Lyapunov function candidate,in term of the time scale decomposition method,which also allows to provide upper bounds on the singularly perturbed parameters.Moreover,it shows that the proposed method for stability analysis can be extended to arbitrary multi-time scale singularly perturbed system.3.To address the control problem for three-dimensional(3D)path following of underactuated AUVs in the presence of unknown internal and external disturbances,a DO is first designed,using the method mentioned above.So that,the problem of control system design given unknown disturbances is reduced to a problem of model-based control.Then,forcing the dynamics into distinct time scales without analysis,a novel composite system control method is proposed.As illustration,it can obviate the increasing complexity of implementation of backstepping by leaving out the interconnection conditions at each step of the design,and thus leads to a simpler path following controller without command derivatives.Moreover,the asymptotically stability for closed-loop system is analyzed by using Lyapunov stability theory and M-matrices method.On the basis of that,the mathematical bound on the control gains is provided.4.Regarding the 3D path following control problem for underactuated AUVs subject to unknown hydrodynamic parameters,external disturbances and input saturation,a DO is first developed to estimate the model uncertainties,in term of the singular perturbation theory.Then,a stabilizing controller is designed based on the composite system method.And the mathematical bound on the control gains is obtained by means of the Lyapunov stability theory.Following that,an anti-windup control strategy is proposed to compensate the impact of input saturation by tuning the control gains.Using the implicit relation among the control gains,the resultant control system is proved still asymptotically stable in the presence of input saturation.Finally,numerical simulation and water-tank experiment are conducted to illustrate the effectiveness of proposed method.This essay focuses on the control design and stability analysis for path following of underactuated AUVs based on the singular perturbation theory.Following that,an novel method has been provided.