Qingxian Wu

Guaranteed transient performance based control with input saturation for near space vehicles

This paper describes the design of guaranteed transient performance based attitude control for the near space vehicle (NSV) with control input saturation using the backstepping method. To improve the robust controllability of the NSV, the parameter adaptive method is used to tackle the integrated effect of unknown time-varying disturbance and control input saturation. Based on the backstepping technique and parameter estimated outputs, a robust attitude control scheme is proposed for the NSV with input saturation. A novel robust attitude control scheme is then proposed based on a prescribed performance bound (PPB) which characterizes the convergence rate and maximum overshoot of the attitude tracking error. The closed-loop system stability under both the developed robust attitude control schemes is proved using Lyapunov’s method and uniformly asymptotical convergence of all closed-loop signals is guaranteed. Finally, simulation results are given to show the effectiveness of both the proposed robust constrained attitude control schemes.

Adaptive fuzzy tracking control for a class of uncertain MIMO nonlinear systems using disturbance observer

In this paper, the adaptive fuzzy tracking control is proposed for a class of multi-input and multioutput (MIMO) nonlinear systems in the presence of system uncertainties, unknown non-symmetric input saturation and external disturbances. Fuzzy logic systems (FLS) are used to approximate the system uncertainty of MIMO nonlinear systems. Then, the compound disturbance containing the approximation error and the time-varying external disturbance that cannot be directly measured are estimated via a disturbance observer. By appropriately choosing the gain matrix, the disturbance observer can approximate the compound disturbance well and the estimate error converges to a compact set. This control strategy is further extended to develop adaptive fuzzy tracking control for MIMO nonlinear systems by coping with practical issues in engineering applications, in particular unknown non-symmetric input saturation and control singularity. Within this setting, the disturbance observer technique is combined with the FLS approximation technique to compensate for the effects of unknown input saturation and control singularity. Lyapunov approach based analysis shows that semi-global uniform boundedness of the closed-loop signals is guaranteed under the proposed tracking control techniques. Numerical simulation results are presented to illustrate the effectiveness of the proposed tracking control schemes.

Maintaining synchronization by decentralized feedback control in time delay neural networks with parameter uncertainties

A decentralized feedback control scheme is proposed to synchronize linearly coupled identical neural networks with time-varying delay and parameter uncertainties. Sufficient condition for synchronization is developed by carefully investigating the uncertain nonlinear synchronization error dynamics in this article. A procedure for designing a decentralized synchronization controller is proposed using linear matrix inequality (LMI) technique. The designed controller can drive the synchronization error to zero and overcome disruption caused by system uncertainty and external disturbance.

Chattering‐free sliding mode control with unidirectional auxiliary surfaces for miniature helicopters

Purpose – This article proposes a chattering‐free sliding mode control scheme with unidirectional auxiliary surfaces (UAS‐SMC) for small miniature autonomous helicopters (Trex 250).Design/methodology/approach – The proposed UAS‐SMC scheme consists of a nested sequence of rotor dynamics, angular rate, Euler angle, velocity and position loops.Findings – It is demonstrated that the UAS‐SMC strategy can eliminate the chattering phenomenon exhibiting in the convenient SMC method and achieve a better approaching speed.Originality/value – The proposed control strategy is implemented on the helicopter and flight tests clearly demonstrate that a much better performance could be achieved, compared with convenient SMC schemes.

Chattering-free condition for sliding mode control with unidirectional auxiliary surfaces

A chattering-free condition is proposed as a sufficient condition for the sliding mode control with unidirectional auxiliary surfaces (UAS-SMC) strategy in a class of non-linear systems. With this condition, the UAS-SMC controller would enjoy the following properties: 1) chattering-free property of the control input; 2) enhanced approaching speed on the switching surfaces (except the original point); 3) no requirement to measure the derivatives; 4) a positively invariant set formed by UAS. The stability of the closed-loop system is demonstrated with a chattering-free UAS-SMC controller. Numerical simulation is given to illustrate the benefits and properties of the proposed controller and algorithm.

Robust control of near-space vehicles with input backlash-like hysteresis

In this article, robust attitude control schemes are proposed for the near-space vehicle with the backlash-like hysteresis and the time-varying unknown disturbance using backstepping technique. In the robust attitude control design, the backlash-like hysteresis is described by a dynamic equation which is decomposed as a linear term and a nonlinear term. To handle the nonlinear term in the dynamic equation of the backlash-like hysteresis and the time-varying unknown disturbance, they are treated as a compounded disturbance and the nonlinear disturbance observer is designed to estimate them. Based on the developed nonlinear disturbance observer, the robust backstepping attitude control is firstly developed for the near-space vehicle. Then, the robust sliding mode attitude control scheme is presented for the near-space vehicle to further enhance the robust attitude control performance. The convergence of all closed-loop signals is rigorously proved via Lyapunov analysis method under the developed robust attitude control schemes. Finally, simulation results are presented to illustrate the effectiveness of the proposed attitude control approaches.

Adaptive recurrent-functional-link-network control for hypersonic vehicles with atmospheric disturbances

The controller design for a near-space hypersonic vehicle (NHV) is challenging due to its plant uncertainties and sensitivity to atmospheric disturbances such as gusts and turbulence. This paper first derives 12 states equations of NHVs subjected to variable wind field, and presents a novel recurrent neural network (RNN) control method for restraining atmospheric disturbances. The method devises a new B-spline recurrent functional link network (BRFLN) and combines it with the nonlinear generalized predictive control (NGPC) algorithm. Moreover, the proportional-derivative (PD) correction BRFLN is proposed to approximate atmospheric disturbances in flight. The weights of BRFLN are online tuned by the adaptive law based on Lyapunov stability theorem. Finally, simulation results show a satisfactory performance for the attitude tracking of the NHV in the mesosphere, and also illustrate the controller’s robustness to wind turbulence.

Robust adaptive backstepping control for a class of uncertain nonlinear systems based on disturbance observers

In this paper, a novel robust adaptive control scheme for a class of uncertain nonlinear systems is proposed using disturbance observer and backstepping method. Firstly, a disturbance observer is developed using radial basis function (RBF) neural network. The parameter updated law of the RBF neural network is given for monitoring subsystem disturbance well. The robust adaptive control scheme is then presented with backstepping method based on the designed disturbance observer. Semiglobal uniform ultimate boundedness (SGUUB) of all signals in the closed-loop uncertain nonlinear system is achieved. The closed-loop system stability analysis shows that semiglobal uniform boundedness of all signals is guaranteed by appropriately choosing design parameters. Finally, two examples are taken to illustrate the effectiveness of the proposed control scheme.

Robust control for a class of time-delay uncertain nonlinear systems based on sliding mode observer

In this paper, a robust control scheme is proposed for a class of time-delay uncertain nonlinear systems with unknown input using the sliding mode observer. The sliding mode state observer is given with radial basis function neural networks, and then the robust control scheme is presented based on the designed sliding mode observer. The developed observer-based control scheme consists of two parts. One term is a linear controller and the other term is a neural network controller. Using the Lyapunov method, a criterion for bounded stability of the closed-loop system is developed in terms of linear matrix inequalities. Finally, a simulation example is used to illustrate the effectiveness of the proposed robust control scheme.

Control-oriented modelling and simulation of thrust misalignment and wind disturbances for hypersonic vehicles

Near-space hypersonic vehicles (NHVs) are viewed as reliable, affordable and global reach vehicles. Their controller design is a challenging task due to strong uncertainties and disturbances in the flight dynamics of NHVs. In this paper, a new methodology is presented to build control-oriented models of two kinds of disturbances. For a winged-cone NHV, the paper models the moment disturbance induced by the thrust misalignment of the engine. Next, a new group of 12-state equations is obtained based on the kinetic and dynamic laws for the NHV with variable wind field, as the wind turbulence frequently occur in the upper near space. Then, the quantisation and simulation results about the models are provided to show the variation characteristics of the disturbances. Finally, the attitude control results are given to assess the adaptive control effect of the NHV with these two models. Therefore, in the presence of the thrust misalignment and wind disturbances, the control-oriented models presented can become t...