Qixun Lan

Global finite-time stabilisation for a class of stochastic nonlinear systems by output feedback

In this paper, the problem of global finite-time stabilisation by output feedback is considered for a class of stochastic nonlinear systems. First, based on homogeneous systems theory and the adding a power integrator technique, a homogeneous reduced order observer and control law are constructed in a recursive manner for the nominal system. Then, the homogeneous domination approach is used to deal with the nonlinearities in drift and diffusion terms; it is shown that the proposed output-feedback control law can guarantee that the closed-loop system is global finite-time stable in probability. Finally, simulation examples are carried out to demonstrate the effectiveness of the proposed control scheme.

Finite-time soft landing on asteroids using nonsingular terminal sliding mode control

Successful future asteroid landing missions require that the control method provides advanced disturbance rejection performance and strong robustness against parameter uncertainties to give higher accuracy and reliability in the complex space environment. Motivated by the requirement for safe and precise soft landing on asteroids, the finite-time soft-landing problem of an asteroid probe is addressed in this paper via a nonsingular terminal sliding mode (NTSM) control technique. The problem is formulated as a two-point boundary-value constraints control problem, where the initial and terminal requirements of the soft-landing problem are all included in the problem formulations. Then, according to the specific characteristics of the problem, an NTSM control law for soft landing on an asteroid is proposed. Simulation results demonstrate that, compared to the widely used traditional sling mode control method, the proposed method provides a much faster convergence rate, higher accuracies, better disturbance rejection properties and stronger robustness against parameter uncertainties.

Finite-time control for soft landing on an asteroid based on line-of-sight angle

Abstract Motivated by the requirement for safe and pinpoint soft landing in future asteroids missions, a soft landing control method based on finite-time control (FTC) technique is developed in this paper. Firstly, in order to utilize the design philosophy of cascaded system, the landing error dynamics of asteroid probe are divided into two subsystems, including a position error subsystem (PES) and a line-of-sight angle error subsystem (LOSAES). Secondly, homogeneous system theory is employed to design the control law for LOSAES such that the states of LOSAES will be stabilized to the origin in finite time. For the reduced PES subsystem, a FTC law is designed such that the rest of states will converge to zero in finite time. Strict analysis shows that the whole system satisfies the finite time stability. Simulation results demonstrate that the proposed method provides faster convergence rates and better disturbance rejection properties compared with the traditional asymptotically stable control (ASC) method.

Global decentralised stabilisation for a class of uncertain large-scale feedforward nonlinear systems

In this paper, the problem of global decentralised stabilisation for a class of uncertain large-scale feedforward nonlinear systems is investigated. The system under consideration is allowed to contain unknown non-Lipschitz continuous nonlinear terms. The design of the global decentralised controllers takes a two steps procedure. First of all, based on the adding a power integrator technique and the homogeneous domination approach a local homogeneous decentralised controller is proposed for each subsystem of the large-scale feedforward nonlinear system. Then, we integrate a series of nested saturation functions with the homogeneous decentralised controllers and adjust the saturation levels to ensure globally asymptotic stability of the closed-loop system. Simulation studies are conducted to illustrate the effectiveness of the proposed control method.

Continuous terminal sliding mode control with extended state observer for PMSM speed regulation system

In this paper, we discuss the speed regulation problem of permanent magnet synchronous motor (PMSM) servo systems. Firstly, a continuous terminal sliding mode control (CTSMC) method is introduced for speed loops to eliminate the chattering phenomenon while still ensuring a strong disturbance rejection ability for the closed-loop system. However, in the presence of strong disturbances, the CTSMC law still needs to select high gain which may result in large steady-state speed fluctuations for the PMSM control system. To this end, an extended state observer (ESO)-based continuous terminal sliding mode control method is proposed. The ESO is employed to estimate system disturbances and the estimation is employed by the speed controller as a feed-forward compensation for disturbances. Compared to the conventional sliding mode control method, the proposed composite sliding control method obtains a faster convergence and better tracking performance. Also, by feed-forward compensating system disturbances and tuning down the gain of the CTSMC law, the fluctuation of steady-state speed of the closed-loop system is reduced while the disturbance rejection capability of the PMSM system is still maintained. Simulation and experimental results are provided to demonstrate the superior properties of the proposed control method.

Finite-Time Control for 6DOF Spacecraft Formation Flying Systems

AbstractThis paper considers the finite-time control problem of 6DOF spacecraft formation flying (SFF) systems in the presence of external disturbances. First of all, based on nonsingular terminal sliding mode (NTSM) method, a local finite-time control law is proposed. Then a finite-time disturbance observer (FTDOB) is introduced to estimate the disturbances, and a composite control law which consists of a feedback control law based on NTSM method and a feed-forward compensation term based on FTDOB technique is constructed such that the follower spacecraft can track the desired trajectory in finite time. The major merit of the proposed method is that chattering is substantially reduced because the switching gain of the discontinuous control law is only required to be greater than the bound of disturbance estimation error rather than that of the disturbances. Furthermore, based on switching control method, continuous NTSM and FTDOB technique, a global finite-time control law is developed for 6DOF SFF syste...

Global decentralised stabilisation for a class of uncertain large-scale high-order upper-triangular nonlinear systems

ABSTRACT This paper considers the global decentralised stabilisation problem for a class of uncertain large-scale high-order upper-triangular nonlinear systems. First, a local linear decentralised controller is recursively constructed based on the generalised homogeneous system theory and the adding a power integrator method. Second, aiming for global stabilisation, a series of nested saturation functions are integrated with the proposed local linear decentralised controller. Then, it is proved that the obtained decentralised saturated controller will render the whole closed-loop system globally asymptotically stable. Due to the flexibility of the generalised homogeneous method, the proposed control approach not only weakens the existing restrictions imposed on the interconnected nonlinearities, but also can be applied to a more general class of upper-triangular nonlinear systems. Furthermore, two simulations examples are conducted to show the effectiveness of the proposed control scheme.

Global decentralized stabilization for a class of large-scale feedforward nonlinear systems

This paper considers the problem of global decentralized stabilization for a class of large-scale feedforward nonlinear systems. First, by using generalized homogeneous systems theory, a local linear decentralized control law is recursively constructed. Second, a series of nested saturation functions are integrated with the proposed local linear control law to render the whole closed-loop large-scale system global asymptotical stability. Due to the flexibility of the generalized homogeneous systems theory, the proposed approach not only weakens the existing restrictions imposed on the interconnected nonlinearities, but also can be applied to more general classes of large-scale feedforward nonlinear systems. Numerical example shows that the effectiveness of the proposed control scheme.