Decentralised sliding mode control for a class of nonlinear interconnected systems

In this paper, a decentralised control strategy based on sliding mode techniques is proposed for a class of nonlinear interconnected systems. Both matched uncertainties in the isolated subsystems and mismatched uncertainties associated with the interconnections are considered. Under mild conditions, sliding mode controllers for each subsystem are designed in a decentralised manner by only employing local information. Conditions are determined which enable information on the interconnections to be employed in decentralised controller design to reduce conservatism. The developed results are applied to an automated highway system. Simulation results pertaining to a high-speed following system are presented to demonstrate the effectiveness of the approach

Nonlinear Sliding Mode Control for Interconnected Systems with Application to Automated Highway Systems

In this paper, a decentralised control strategy based on sliding mode techniques is proposed for a class of nonlinear interconnected systems. Both matched uncertainties in the isolated subsystems and mismatched uncertainties associated with the interconnections are considered. Under mild conditions, sliding mode controllers for each subsystem are designed in a decentralised manner by only employing local information. Conditions are determined which enable information on the interconnections to be employed within the decentralised controller design to reduce conservatism. The developed results are applied to an automated highway system. Simulation results pertaining to a high-speed following system are presented to demonstrate the effectiveness of the approach

Decentralised sliding mode control for nonlinear interconnected systems in the regular form

In this paper, a decentralised control strategy based on sliding mode techniques is proposed for a class of nonlinear interconnected systems in regular form. All the isolated subsystems and interconnections are fully nonlinear. It is not required that the nominal isolated subsystems are either linearizable or partially linearizable. The uncertainties are nonlinear and bounded by nonlinear functions. Specifically, uncertainties in the input distribution and interconnections are considered. Under mild conditions, sliding mode controllers for each subsystem are designed by only employing local information. Sufficient conditions are developed under which information on the interconnections is employed for decentralised controller design to reduce conservatism. The bounds on the uncertainties have more general forms compared with previous work. A simulation example is used to demonstrate the effectiveness of the proposed method

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 Sliding Mode Tracking Control for a Class of Nonlinear Interconnected Systems

This paper proposes a decentralised tracking control scheme for a class of nonlinear interconnected systems using sliding mode techniques. The desired output signals are time-varying. Both matched uncertainty and mismatched unknown interconnections are considered. Using geometric transformation, the considered system is transferred to a system with a unique structure to facilitate both the design of the sliding surface and the decentralised controllers. The sliding surface is designed based on the tracking error. A set of conditions are proposed to guarantee that when sliding motion occurs, the tracking errors converge to zero asymptotically while the system states are bounded. Decentralised controllers are then designed so that the interconnected systems' states can be driven to the designed sliding surface. Finally, simulation of a coupled inverted pendulum system demonstrates the results

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

Decentralised sliding mode control for nonlinear interconnected systems in the generalised regular form

In this paper, a decentralised control strategy based on sliding mode techniques is proposed for a class of nonlinear interconnected systems in generalised regular form. All the isolated subsystems and interconnections are fully nonlinear. It is not required that the nominal isolated subsystems are either linearizable or partially linearizable. The uncertainties are nonlinear and bounded by known functions. Under mild conditions, sliding mode controllers for each subsystem are designed by only employing local information. Su?cient conditions are developed under which information on the interconnections is employed for decentralised controller design to reduce the e?ects of the interconnections on the entire systems. The bounds on the uncertainties have more general forms compared with previous work. A simulation example is used to demonstrate the e?ectiveness of the proposed method

Decentralised sliding mode control for nonlinear interconnected systems in the generalised regular form

In this paper, a decentralised control strategy based on sliding mode techniques is proposed for a class of nonlinear interconnected systems in generalised regular form. All the isolated subsystems and interconnections are fully nonlinear. It is not required that the nominal isolated subsystems are either linearizable or partially linearizable. The uncertainties are nonlinear and bounded by known functions. Under mild conditions, sliding mode controllers for each subsystem are designed by only employing local information. Su?cient conditions are developed under which information on the interconnections is employed for decentralised controller design to reduce the e?ects of the interconnections on the entire systems. The bounds on the uncertainties have more general forms compared with previous work. A simulation example is used to demonstrate the e?ectiveness of the proposed method

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