Rongjie Liu

Nested saturation control for overhead crane systems

This paper presents a new control strategy for overhead crane systems. First, by utilizing a coordinate change, the underactuated overhead crane dynamical model can be transformed into an upper-triangular form. Second, a finite-time controller is designed based on the nonlinear nested saturation and adding a power integrator technique. Rigorous proof shows that the controller can guarantee finite-time stability of the closed-loop system. Simulations show the effectiveness of the proposed method.

Optimal integral sliding mode control scheme based on pseudospectral method for robotic manipulators

For a multi-input multi-output nonlinear system, an optimal integral sliding mode control scheme based on pseudospectral method is proposed in this paper. And the controller is applied on rigid robotic manipulators with constraints. First, a general form of integral sliding mode is designed with the aim of restraining disturbance. Then, pseudospectral method is adopted to deal with constrained optimal control problem. In consideration of the benefits of both methods, an optimal integral sliding mode controller is given, which is based on the combination of integral sliding mode and pseudospectral method. The stability analysis shows that the controller can guarantee stability of robotic manipulator system. Simulations show the effectiveness of proposed method.

Suboptimal Integral Sliding Mode Controller Design for a Class of Affine Systems

This paper proposes an nth-order suboptimal integral sliding mode controller for a class of nonlinear affine systems. First, a general form of integral sliding mode is given. An extended Theta-D method is developed for the optimal control problems characterized by a quadratic cost function with a cross term. Then the extended Theta-D method is employed to determine a suboptimal integral sliding mode. Rigorous proof shows that the controller guarantees semi-global asymptotical stability of affine systems. To verify the accuracy of the extended Theta-D method, a numerical example is provided. To verify the effectiveness of the proposed suboptimal integral sliding mode controller, a numerical example and an application example of an overhead crane system are provided.

Global practical tracking of a class of nonlinear systems using linear sampled-data control

This paper considers the problem of global practical tracking via sampled-data control for a class of uncertain nonlinear systems. Under a lower triangular linear growth condition, a sampled-data state feedback controller is first constructed such that the states are globally bounded and the error between the system output and the reference signal will be rendered smaller than a given tolerance. When only the output of the system is measurable, a sampled-data output feedback controller, whose observer and control law are both linear, is constructed to solve the global practical tracking problem.

Decentralized output feedback control of a class of nonlinear systems with unsynchronized sampling instants

Even though the interconnected subsystems of a class of nonlinear systems are controlled by the same sampling period, it is common that the sampled-data time instant of each subsystem is different. In this case, the problem of using sampled-data output feedback to design global decentralized stabilizers for the decentralized systems is quite challenging but also interesting. To solve this problem, in this paper we propose a methodology to construct a set of decentralized stabilizers, which are implemented using the unsynchronized sampling instants.

Decentralized sampled-data control of interconnected systems using low gain and high gain output feedback

In practice, it is common that the interconnected subsystems of a large-scale system are controlled by decentralized sampled-data stabilizers. In this case, the problem of using sampled-data output feedback to design global a decentralized stabilizer for the large-scale systems is quite challenging. To solve the problem, in this paper we propose a gain domination method that implements both low- and high- gains to negate the effects of nonlinearities found in a series of interconnected systems. The decentralized stabilizers with low gain and high gain are implemented using sampled-data output feedbacks.

An optimal integral sliding mode control strategy based on a pseudospectral method for a class of affine systems

This paper presents an optimal integral sliding mode control method based on a pseudospectral method for a class of affine systems with state and control constraints. First, a general form of an integral sliding mode is presented. Integral sliding mode control cannot deal with the problem of states and control constraints, nor can it satisfy the minimization of the cost function. The pseudospectral method has a high convergence speed and performs well in solving optimal control problems with general performance index, endpoint conditions and path constraints. In consideration of these advantages, an optimal integral sliding mode controller is determined by the pseudospectral method. Then, the stability analysis of optimal pseudospectral sliding mode method is discussed. Finally, numerical simulations show the effectiveness of the proposed method. An application example, consisting of an overhead crane system, is investigated to demonstrate the effectiveness and robustness of the proposed technique.

Global practical tracking for a class of nonlinear systems via linear sampled-data control

This paper considers the problem of global practical tracking via state feedback sampled-data control for a class of uncertain nonlinear systems. Under a lower-triangular linear growth condition, a sampled-data state feedback controller is constructed such that the states are globally bounded and the error between the system output and the reference signal will be rendered smaller than a given tolerance. The proposed state feedback sampled-data controllers are linear and can be easily implemented in practice.