Zhilin Liu

Containment control of autonomous surface vehicles: A nonlinear disturbance observer–based dynamic surface control design:

This study presents a solution to the problem of containment control of multiple fully actuated autonomous surface vehicles subject to environmental disturbances. Using finite-time stability theory, a nonlinear disturbance observer is constructed to provide an estimation of unknown disturbances online. By employing nonlinear disturbance observer to compensate disturbances, a robust containment controller is constructed by combining backstepping technique and dynamic surface control technique. It is proved that the proposed containment control scheme can force all the followers to move into the convex hull spanned by the leaders and guarantee that all the signals in the closed-loop system are globally uniformly ultimately bounded. Finally, four simulation examples are provided to demonstrate the effectiveness of the containment controller and its robustness to external disturbances.

Predictive control for multi-joint manipulator with polytopic model

A model predictive control (MPC) is proposed for a multi-joint manipulator with constrained input. With linearization around the equilibrium manifold, the manipulator was transformed into a continous linear parameter varying system with respect to the equilibrium manifold. The corresponding manipulator system is described as polytopic expression by a convex decomposition. The control law is obtained by convex optimization based on MPC involving linear matrix inequalities (LMIs). Closed-loop systems stability is guaranteed by LMI constrain. The simulation results verify the effectiveness of the proposed method.

Containment Control of Underactuated Ships with Environment Disturbances and Parameter Uncertainties

An implementable robust containment control algorithm is proposed for a group of underactuated ships in the presence of hydrodynamic parameter uncertainties and external disturbances. The control objective is to drive all the followers into the convex hull spanned by the virtual leaders, whose state information is available only to a subset of the followers. For this purpose, the ship model is primarily transformed to a strict-feedback form. In the kinematic design, a virtual containment controller, requiring the state information from its neighbors, is presented based on the results obtained from graph theory. In the dynamic design, a robust containment controller is developed through utilizing upper-to-up sliding mode control. In addition, in order to simplify the implementations of the control law, the command filtered backstepping (CFBP) method is introduced to prevent the analytic differentiations of the virtual law from each design step of the backstepping (BP) method. Subsequently, it is well proven that all the tracking errors could converge to and remain small neighborhoods of the equilibrium point. Finally, several simulation experiments are conducted to demonstrate the performance of the proposed control algorithm.

Predictive control for straight path following of underactuated surface vessels with roll constraints

The strong time-varying disturbances from sea waves such as wind, wave and current probably lead to large roll motion of marine surface vessels, which makes the roll angle out of the safety range. The roll motion severely affects the performance and stability of path following control system. A novel robust model predictive control (RMPC) method with roll constraints is proposed based on mixed H2 / H∞ control approach. The polyhedral model with coupled surge, sway, roll and yaw is constructed in different working ranges of the rudder angle. Then, RMPC method is proposed based on mixed H2 / H∞ control approach. The roll angle constraint, input constraints and performance index are transformed into the convex optimization of linear matrix inequalities (LMIs). The tight constraints of the invariant ellipsoid ensure the close loop system uniformly bounded. The simulation is provided to demonstrate the effectiveness of the proposed algorithm. The roll angle is in the constrained range and the control system has the robustness to reject time-varying disturbances.

H ∞ control for time-delay piecewise affine with constrained ellipsoid

This paper dealt with the stabilization problem of a discrete-time piecewise affine (PWA) systems with time-delay. An H∞ state feedback controller design is proposed, and the PWA system was described as ellipsoid which characterized by a set of vector inequalities..thereby the constraint of linear matrix inequalities (LMIs) was released. In terms of LMIs, the time-delay PWA system was stabilized in Lyapunov theory, and the minimum problem of the H∞ performance index can be cast as a convex optimization problem with LMIs constraints. The simulation results verified the effectiveness of the proposed method.