Delay-independent decentralised output feedback control for large-scale systems with nonlinear interconnections

In this paper, a stabilisation problem for a class of large-scale systems with nonlinear interconnections is considered. All the uncertainties are nonlinear and are subject to the effects of time delay. A decentralised static output feedback variable structure control is synthesised and the stability of the corresponding closed-loop system is analysed based on the Lyapunov Razumikhin approach. A set of conditions is developed to guarantee that the large-scale interconnected system is stabilised uniformly asymptotically. Further study shows that the conservatism can be reduced by employing additive controllers if the known interconnections are separated into matched and mismatched parts. It is not required that the subsystems are square. The designed controller is independent of time delay and thus it does not require memory. Simulation results show the effectiveness of the proposed approach

Stabilisation of Time Delay Systems with Nonlinear Disturbances Using Sliding Mode Control

This paper focuses on a class of control systems with delayed states and nonlinear disturbances using sliding mode techniques. Both matched and mismatched uncertainties are considered which are assumed to be bounded by known nonlinear functions. The bounds are used in the control design and analysis to reduce conservatism. A sliding function is designed and a set of sufficient conditions is derived to guarantee the asymptotic stability of the corresponding sliding motion by using the Lyapunov-Razumikhin approach which allows large time varying delay with fast changing rate. A delay dependent sliding mode control is synthesised to drive the system to the sliding surface in finite time and maintain a sliding motion thereafter. Effectiveness of the proposed method is demonstrated via a case study on a continuous stirred tank reactor system

Decentralised sliding mode control for nonlinear interconnected systems with uncertainties

With the advances in science and technology, nonlinear large-scale interconnected systems have widely appeared in the real life. Traditional centralised control methods have inevitable disadvantages when they are used to deal with complex nonlinear interconnected systems with uncertainties. In connection with this, people desire to develop the novel control strategy which can be applied to complex interconnected systems. Therefore, decentralised sliding mode control (SMC) for interconnected systems has attracted great attention in related fields due to its advantages, for instance, simple structure, low cost of calculation, fast response, reduced-order sliding mode dynamics and insensitivity to matched variation of parameters and disturbances in systems. This thesis focuses on the development of decentralised SMC for nonlinear interconnected systems with uncertainties under certain assumptions. Several methods and different techniques have been considered in design of the controller to improve the robustness. The main contributions of this thesis include: • The state feedback decentralised SMC is developed for nonlinear interconnected systems with matched uncertainty and mismatched unknown interconnections. A state feedback decentralised SMC strategy, under the assumption that all system states are accessible, is proposed to attenuate the impact of the uncertainties by using bounds on uncertainties and interconnections. The bounds used in the design are fully nonlinear which provide higher applicability for different complex interconnected systems. Especially, for this fully nonlinear system, the proposed method does not need to use the technique of linearisation, which is widely used in existing work to deal with nonlinear interconnected systems with uncertainties. • The dynamic observer is applied to complex nonlinear interconnected systems with matched and mismatched uncertainties. This dynamic observer can estimate the system states which can not be achieved during the controller design. The proposed method has great identification ability with small estimated errors for the states of nonlinear interconnected systems with matched and mismatched uncertainties. It should be pointed out that the considered uncertainties of nonlinear interconnected systems have general forms, which means that the proposed method can be effectively used in more generalised nonlinear interconnected systems. • A variable structure observer-based decentralised SMC is proposed to control a class of nonlinear interconnected systems with matched and mismatched uncertainties. Based on the designed dynamic observer, a dynamic decentralised output feedback SMC using outputs and estimated states is presented to control the interconnected systems with matched and mismatched uncertainties. The nonlinear interconnections are employed in the control design to reduce the conservatism of the developed results. The bounds of the uncertainties are relaxed which are nonlinear and take more general forms. Moreover, the limitation for the interconnected system is reduced when compared with the existing results in which the proposed strategies adopt the full-order observer. Besides that, the presented method improves the robustness of nonlinear interconnected systems to be against the effects of uncertainties. This thesis also provides several numerical and practical simulations to demonstrate the effectiveness of the proposed decentralised SMC for nonlinear interconnected systems with matched uncertainty, mismatched uncertainty and nonlinear interconnections

State Feedback Sliding Mode Control of Complex Systems with Applications

This thesis concerns the development of robust nonlinear control design for complex systems including nonholonomic systems and large-scale systems using sliding mode control (SMC) techniques under the assumption that all system state variables are accessible for design. The main developments in this thesis include: 1). The concept of generalised regular form and design of a novel sliding function. The mathematical definition of generalised regular form is proposed for the first time. It is an extension of the classical regular form, which makes SMC applicable to a wider class of nonlinear systems. A novel sliding function design, which is based on the global implicit function theorem, is proposed to guarantee unique sliding mode dynamics. 2). The development of decentralised SMC for large-scale interconnected systems. For systems with uncertain interconnections which possess the superposition property, a decentralised control scheme is presented to counteract the effect of the uncertainty by using bounds on uncertainties and interconnections. The bounds used in the design are nonlinear functions instead of constant, linear or polynomial functions. The design strategy has also been expanded to a fully nonlinear case for interconnected systems in the generalised regular form. 3). Robust decentralised SMC for a class of nonlinear systems with uncertainties in input distribution. A system with uncertainties in input distribution is full of challenges. A novel method is proposed to deal with such uncertainties for a class of nonlinear interconnected systems. The designed decentralised SMC enhances the robustness of the controlled systems. This thesis also provides case studies of three applications for the proposed approaches. The existence of the generalised regular form is verified in the trajectory tracking control of a wheeled mobile robot (WMR) system. Both simulations and experiments on the WMR are given to demonstrate the validity and effectiveness of the generalised regular form-based SMC design. A continuous stirred tank reactor (CSTR) system and a longitudinal vehicle-following system are used to test the proposed decentralised SMC schemes. An expanded vehicle-following system with both longitudinal and lateral controllers has been developed to demonstrate the robust control design for system with uncertainties in input distribution

Decentralised Stabilisation of Nonlinear Time Delay Interconnected Systems

A decentralised state feedback control scheme is proposed to stabilise a class of nonlinear interconnected systems asymptotically based on the characteristics of the system structure. Under the condition that all the nominal isolated subsystems have uniform relative degree, the considered class of interconnected systems is transferred to a new interconnected system formed of single input systems, which facilitates the decentralised control design. A new term, weak mismatched uncertainty, is introduced for the first time to recognise a class of mismatched uncertainties in the isolated subsystems. The study shows that the effects of both matched and weak mismatched uncertainties in the isolated subsystems can be rejected completely by appropriate choice of control, and the effects of matched interconnections can be largely reduced if the control gain is sufficiently high

Recent advances on recursive filtering and sliding mode design for networked nonlinear stochastic systems: A survey

Copyright © 2013 Jun Hu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Some recent advances on the recursive filtering and sliding mode design problems for nonlinear stochastic systems with network-induced phenomena are surveyed. The network-induced phenomena under consideration mainly include missing measurements, fading measurements, signal quantization, probabilistic sensor delays, sensor saturations, randomly occurring nonlinearities, and randomly occurring uncertainties. With respect to these network-induced phenomena, the developments on filtering and sliding mode design problems are systematically reviewed. In particular, concerning the network-induced phenomena, some recent results on the recursive filtering for time-varying nonlinear stochastic systems and sliding mode design for time-invariant nonlinear stochastic systems are given, respectively. Finally, conclusions are proposed and some potential future research works are pointed out.This work was supported in part by the National Natural Science Foundation of China under Grant nos. 61134009, 61329301, 61333012, 61374127 and 11301118, the Engineering and Physical Sciences Research Council (EPSRC) of the UK under Grant no. GR/S27658/01, the Royal Society of the UK, and the Alexander von Humboldt Foundation of Germany

Decentralised control for complex systems - An invited survey

© 2014 Inderscience Enterprises Ltd. With the advancement of science and technology, practical systems are becoming more complex. Decentralised control has been recognised as a practical, feasible and powerful tool for application to large scale interconnected systems. In this paper, past and recent results relating to decentralised control of complex large scale interconnected systems are reviewed. Decentralised control based on modern control approaches such as variable structure techniques, adaptive control and backstepping approaches are discussed. It is well known that system structure can be employed to reduce conservatism in the control design and decentralised control for interconnected systems with similar and symmetric structure is explored. Decentralised control of singular large scale systems is also reviewed in this paper

System structure based decentralized sliding mode output tracking control for nonlinear interconnected systems

In this article, a decentralized tracking control scheme is proposed for a class of nonlinear interconnected systems with uncertainties using sliding mode technique. Both matched nonlinear uncertainty and mismatched known nonlinear interconnections are considered. Under the condition that the nominal isolated subsystems have relative degrees, a geometric transformation is applied to transfer the interconnected system into a new nonlinear interconnected system with a special structure to facilitate the system analysis and design. Then, a composite sliding surface is designed in terms of tracking errors, and decentralized controllers are proposed to drive the system states to the designed sliding surface in finite time and maintain a sliding motion on it thereafter. A set of conditions are developed to guarantee that the output tracking errors converge to zero asymptotically while all system state variables are bounded. The considered interconnected systems are nonlinear and it is not required that either the isolated subsystems or the isolated nominal subsystems are linearizable. The desired output signals are allowed to be time-varying. Finally, the developed results are applied to an inverted coupled-pendulum system. Simulation demonstrates that the proposed control scheme is effective