Showing papers by "Guo-Ping Liu published in 2007"
TL;DR: A new method is proposed for stability analysis of neural networks (NNs) with a time-varying delay by considering the additional useful terms, which were ignored in previous methods, when estimating the upper bound of the derivative of Lyapunov functionals and introducing the new free-weighting matrices.
Abstract: In this letter, a new method is proposed for stability analysis of neural networks (NNs) with a time-varying delay. Some less conservative delay-dependent stability criteria are established by considering the additional useful terms, which were ignored in previous methods, when estimating the upper bound of the derivative of Lyapunov functionals and introducing the new free-weighting matrices. Numerical examples are given to demonstrate the effectiveness and the benefits of the proposed method
503 citations
TL;DR: It is shown that a closed-loop NPC system with bounded random network delay is stable if its corresponding switched system is stable, and the effectiveness of the novel networked predictive control scheme is shown.
Abstract: The design problem of networked control systems (NCS) with constant and random network delay in the forward and feedback channels, respectively, is considered in this paper. A novel networked predictive control (NPC) scheme is proposed to overcome the effects of network delay and data dropout. Stability criteria of closed-loop NPC systems are presented. The necessary and sufficient conditions for the stability of closed-loop NCS with constant time delay are given. Furthermore, it is shown that a closed-loop NPC system with bounded random network delay is stable if its corresponding switched system is stable. Both simulation study and practical experiments show the effectiveness of the control scheme
436 citations
TL;DR: Some improved delay/interval-dependent stability criteria for NNs with time-varying interval delay are proposed andumerical examples are given to demonstrate the effectiveness and the merits of the proposed method.
Abstract: This letter is concerned with the stability analysis of neural networks (NNs) with time-varying interval delay. The relationship between the time-varying delay and its lower and upper bounds is taken into account when estimating the upper bound of the derivative of Lyapunov functional. As a result, some improved delay/interval-dependent stability criteria for NNs with time-varying interval delay are proposed. Numerical examples are given to demonstrate the effectiveness and the merits of the proposed method.
318 citations
TL;DR: The study demonstrates that the belief rule based system is flexible, can be adapted to represent complicated expert systems, and is a valid novel approach for pipeline leak detection.
Abstract: Belief rule based expert systems are an extension of traditional rule based systems and are capable of representing more complicated causal relationships using different types of information with uncertainties. This paper describes how the belief rule based expert systems can be trained and used for pipeline leak detection. Pipeline operations under different conditions are modelled by a belief rule base using expert knowledge, which is then trained and fine tuned using pipeline operating data, and validated by testing data. All training and testing data are collected and scaled from a real pipeline. The study demonstrates that the belief rule based system is flexible, can be adapted to represent complicated expert systems, and is a valid novel approach for pipeline leak detection.
247 citations
01 Mar 2007
TL;DR: Simulation and real-time results give an illustration of the proposed control strategies and the necessary and sufficient conditions on the stability of the closed-loop NCS are derived, which provides useful analytical stability criteria.
Abstract: This paper is concerned with the design of networked control systems (NCSs) with random network delay in the feedback channel and gives stability criteria of closed-loop networked predictive control systems. The principle of predictive control is adopted to overcome the effects of network time delay. The necessary and sufficient conditions on the stability of the closed-loop NCS are derived, which provides useful analytical stability criteria. The closed-loop networked predictive control system with bounded random network delay is stable if the corresponding switched system is stable. Simulation and real-time results give an illustration of the proposed control strategies
238 citations
TL;DR: In this paper, a nonlinear control method for multivariable systems with time delay is presented, which is based on a unique active disturbance rejection (ADRC) concept, and consists of the tracking differentiator, the extended state observer and the nonlinear proportional derivative (PD) controller.
Abstract: A new nonlinear control method for multivariable systems with time delay is presented. It is based on a unique active disturbance rejection concept. The proposed active disturbance rejection controller (ADRC) consists of the tracking differentiator, the extended state observer and the nonlinear proportional derivative (PD) controller. In this approach, the systems with time delay in the input are viewed as higher-order systems without time delay in the input, the approximation error between the nominal systems and real systems and other uncertainties, all of which are seen as `disturbance' by ADRC and are actively compensated. The techniques developed here can be effectively used in engineering systems, such as chemical processes, and this is demonstrated by an example.
194 citations
TL;DR: A new event-driven NPC method is considered where the control signal is selected according to the plant output rather than the time delay measurement, which can significantly improve the system performance in the presence of model uncertainty.
Abstract: In networked control systems, random transmission delay significantly degrades the control performance and can cause system instability. To address this problem, the method of networked predictive control (NPC) has been proposed, which takes advantage of the feature of the network that a packet of data can be transferred simultaneously. At the controller side, future control sequences for every possible time delay are generated, which are then packed into a single packet and transmitted to the plant side. The plant side receives the packet and chooses the proper control signal based on the time delay measurement. However, this scheme needs an accurate plant mathematical model and the measurement of time delay. In this paper, a new event-driven NPC method is considered where the control signal is selected according to the plant output rather than the time delay measurement. The new method does not need any time delay measurement and can significantly improve the system performance in the presence of model uncertainty. The stability of the system when the method is used is analyzed. To illustrate the improved performance using the proposed method, the results from both simulations and real Internet-based networked experiments for a servo system are presented
120 citations
TL;DR: By the so-called lifting method, time-delay systems are transformed into delay-free systems such that simple necessary and sufficient conditions have been developed for the stability analysis of systems with constant delays.
Abstract: In this article, the problems of stability and stabilization for systems with both constant and time-varying delays have been considered. By the so-called lifting method, time-delay systems are transformed into delay-free systems such that simple necessary and sufficient conditions have been developed for the stability analysis of systems with constant delays. For systems with time-varying delays, they have been converted to a switched system so that the existing results can be applied to analyze the problems of stability and stabilization. Linear matrix inequality (LMI) approach has been employed to the state feedback control design. Numerical examples are given to show the effectiveness of the proposed technique.
85 citations
TL;DR: In this article, an improved stability criterion for networked closed-loop systems is proposed without ignoring any terms in the derivative of Lyapunov-Krasovskii function.
Abstract: The controller design problem for networked control systems (NCSs) is investigated. By considering the relationship between the network-reduced delay and its upper bound, an improved stability criterion for networked closed-loop system is proposed without ignoring any terms in the derivative of Lyapunov-Krasovskii function. As a result, a state feedback controller design method is established using a modified cone complementary linearisation (CCL) algorithm with a new stopping condition. A numerical example is given to demonstrate the effectiveness and the benefits of the proposed method.
80 citations
TL;DR: In this paper, a predictor in discrete time is introduced, which converts the original system with input delay to an equivalent system without the explicit appearance of time delay and makes the control problem solvable.
Abstract: The problem of sliding-mode control is investigated for a class of uncertain linear systems with input-delay in discrete time. First, a predictor in discrete time is introduced, which converts the original system with input delay to an equivalent system without the explicit appearance of time delay and makes the control problem solvable. Then, sliding-mode controls are constructed for both systems with and without bounded disturbance. Simulation studies show the effectiveness of the control scheme.
80 citations
15 Apr 2007
TL;DR: A switched system's method has been proposed, which solves the stochastic problem in a deterministic way and presents a new control scheme, which is termed networked predictive control.
Abstract: The paper is concerned with the design and stability analysis of networked control systems with random network delay, which are described in a state-space form. It presents a new control scheme, which is termed networked predictive control. This scheme mainly consists of the control prediction generator and network delay compensator. The control prediction generator provides a set of future control predictions to make the closed-loop system achieve the desired control performance and the network delay compensator removes the effects of the network transmission delay. The stability criteria of the closed-loop networked predictive control systems are analytically derived for fixed. In case of random network delay, a switched system's method has been proposed, which solves the stochastic problem in a deterministic way.
TL;DR: In this paper, the authors present a record of controlled testing to establish the validity of the Taguchi method in this context, using an industry-standard synthetic yarn as a base line for the research.
Abstract: Yarn splicing joins two yarns by applying a blast of compressed air into a profiled device called a splicing chamber. Splicing is a mature technology, but there is little published work on its fundamental principles. The current research program addresses these principles. However, the research confronts many variables such as yarn count and construction. The Taguchi design of experiment method can simplify the research, by reducing the amount of testing. This article presents a record of controlled testing to establish the validity of the Taguchi method in this context. The tests were performed using an industry-standard synthetic yarn as a base line for the research. The article reports on the Taguchi analysis of results and its effectiveness in optimizing splicer parameters to produce a strong splice with minimum variation. Later, articles will apply the technique to results of work on different yarns, assessing splice aesthetics, yarn characteristics, and splicing chamber geometry with the ob...
TL;DR: In this article, the problem of state feedback and output feedback control of a class of continuous-time linear systems with delayed measurements is addressed, and sufficient conditions for the existence of the state feedback controller and the output feedback controller are derived in terms of linear matrix inequalities.
Abstract: This paper is concerned with the problem of state feedback and output feedback control of a class of nonlinear systems with delayed measurements. This class of nonlinear systems is made up of continuous-time linear systems with nonlinear perturbations. The nonlinearity is assumed to satisfy a global Lipschitz condition and the time delay is assumed to be time-varying and have no restriction on its derivative. On the basis of the Lyapunov-Krasovskii approach, sufficient conditions for the existence of the state feedback controller and the output feedback controller are derived in terms of linear matrix inequalities. Methods of calculating the controller gain matrices are also presented. Two numerical examples are given to illustrate the effectiveness of the proposed methods. (C) 2006 Elsevier Ltd. All rights reserved.
TL;DR: A new method is proposed to estimate the upper bound of the derivative of Lyapunov functional without ignoring some useful terms and improved delay-dependent stability criteria are established by taking into account the range for the time-delay.
TL;DR: In this article, an augmented Lyapunov functional is introduced to establish some improved delay-dependent stability criteria using a simple and alternative proving method, and the resulting criteria are extended to the stability analysis of systems with time-varying structured uncertainties.
Abstract: The stability problem of systems with a time-varying interval delay is investigated. An augmented Lyapunov functional is introduced to establish some improved delay-dependent stability criteria using a simple and alternative proving method. It is shown that some recently published results are the special cases considered here. The resulting criteria are extended to the stability analysis of systems with time-varying structured uncertainties. A numerical example is given to demonstrate the benefits and effectiveness of the proposed method.
TL;DR: The criteria for the existence and uniqueness of the globally optimal solutions are established using the high matrix, optimal max-only projection set and ks-control vector of max–min functions.
Abstract: A variety of problems in computer science, operations research, control theory, etc., can be modeled as non-linear and non-differentiable max---min systems. This paper introduces the global optimization into such systems. The criteria for the existence and uniqueness of the globally optimal solutions are established using the high matrix, optimal max-only projection set and k s -control vector of max---min functions. It is also shown that the global optimization can be accomplished through the partial max-only projection representation with algebraic and combinatorial features. The methods are constructive and lead to an algorithm of finding all globally optimal solutions.
16 Aug 2007
TL;DR: An algorithm HPSOA (hybrid particle swarm optimization algorithm) is presented to resolve dynamic Web services selection with QoS global optimal in grid workflow to solve the QoSglobal optimal problem.
Abstract: The service oriented grid workflow has been a research focus in grid technology. As an NP complete problem, grid service scheduling is difficult to solve by means of classic algorithms This paper presents an algorithm HPSOA (hybrid particle swarm optimization algorithm) to resolve dynamic Web services selection with QoS global optimal in grid workflow.The essence of the algorithm is that the problem of dynamic Web Service selection with QoS global optimal is transformed into a multi-objective services composition optimization with QoS constraints. The operations of the cross and mutation in genetic algorithm are brought into PSOA (particle swarm optimization algorithm) to form a mix algorithm, which called HPSOA solve the QoS global optimal problem. Theoretical analysis and experimental results indicate the feasibility and efficiency of the algorithm.
15 Apr 2007
TL;DR: The paper analyzes characteristics of Ethernet and embedded microprocessor, discusses the hardware structure design (modularization design) of a test platform for networked control systems, which is named NetCon, and shows that NetCon has a trustworthy reliability and validity.
Abstract: The paper analyzes characteristics of Ethernet and embedded microprocessor, discusses the hardware structure design (modularization design) of a test platform for networked control systems, which is named NetCon. A networked brushless DC motor control experiment is made using the platform. From the experiment, it is shown that NetCon has a trustworthy reliability and validity. Furthermore, NetCon makes the research of NCS deeper from the theoretical research to the practical application research and enriches the research of NCS.
15 Apr 2007
TL;DR: A least square method is considered which is applied to compress the control sequence before it is send to the network to solve the problem of random time delay and frequency data dropout.
Abstract: Random time delay and frequency data dropout can degrade the performance of networked control systems and even cause system instability. Liu et al. (2004) introduced a networked model based predictive control scheme to tackle this problem. In his method, a set of control sequences for every possible delay time are packed together and sent to the plant side, and on the plant side the relevant control signal corresponding to the measured time delay is selected. It is an effective method to compensate for the network delay. However, it raises a new problem that it would increase the network traffic, because a sequence requires more transmitting time than a single value. To solve this problem, this paper consider a least square method which is applied to compress the control sequence before it is send to the network.feedback control system
15 Apr 2007
TL;DR: A simplified generalized predictive control (GPC) algorithm of networked control systems is presented through adding a simulated GPC controller which starts to run earlier, and the feasibility and effectiveness of the proposed algorithm are shown.
Abstract: This paper is concerned with a simplified GPC algorithm of networked control systems. Networked predictive control is recently used to cope with the random and uncertain time delay induced by network transmission. Instead of predicting a set of control sequences at one sampling period in former networked predictive control systems, a simplified generalized predictive control (GPC) algorithm is presented through adding a simulated GPC controller which starts to run earlier. The outputs of simulated GPC controller are sent to a buffer then multiplexed with that of practical GPC controller together. Thus only two computation step of GPC controller are required to produce the total control sequences. Moreover, traditional GPC controllers can be used to build the networked predictive control systems without any change except the delay compensator added. The off-line and real-time simulations show the feasibility and effectiveness of the proposed algorithm.
01 Jul 2007
TL;DR: In this article, a delay-dependent robust stability for time-delay systems with nonlinear perturbations is studied. And the authors propose a new method to estimate the upper bound of the derivative of the Lyapunov functional without ignoring some useful terms.
Abstract: This paper studies the delay-dependent robust stability for time-delay systems with nonlinear perturbations. A new method is proposed to estimate the upper bound of the derivative of Lyapunov functional without ignoring some useful terms. Improved delay-dependent stability criteria are established by taking into account the range for the time-delay. In addition, augmented Lyapunov functionals are introduced to derive less conservative delay-dependent stability conditions. Finally, numerical examples are given to demonstrate the effectiveness and the merits of the proposed method.
01 Dec 2007
TL;DR: Using average dwell time method, the sufficient conditions guaranteeing exponential stability are derived in the case of actuator or controller failure and are used to show the effectiveness of the proposed method.
Abstract: This paper studies the problem of actuator or controller failure of a class of time-varying delay systems. It is assumed once the actuator or controller fails, the system becomes unstable. It addresses how long and how frequent the failure is so that the system can keep exponentially stable. Based on a switching method, this kind of failure problems is converted into one of finding a switching signal to stabilize the corresponding switched delay system. Then using average dwell time method, the sufficient conditions guaranteeing exponential stability are derived in the case of actuator or controller failure. A numerical example is used to show the effectiveness of the proposed method.
15 Apr 2007
TL;DR: The software architecture is presented in which a client/server structure is constructed to deal with the case where there are many users who want to access the system information and even change system parameters online and dynamically, an access control module is designed to make this process controllable and safe.
Abstract: The supervisory software has widely been applied in various areas for many years. This paper introduces the design of supervisory software which is a part of a practical implementation platform for the ethernet-based control systems. The software architecture is presented in which a client/server structure is constructed to deal with the case where there are many users who want to access the system information and even change system parameters online and dynamically, an access control module is designed to make this process controllable and safe, friendly human machine interface (HMI) makes it very easy to configure signals and parameters that need to be monitored or controlled according to the users' demands.
TL;DR: A networked control and supervision system (NCSS) based on LonWorks fieldbus and Intranet/Internet was designed, which was composed of the universal intelligent control nodes (ICNs), the visual control and supervised configuration platforms (VCCP and VSCP) and an Intranets/Internet-based remote supervision platform (RSP).
Abstract: A networked control and supervision system (NCSS) based on LonWorks fieldbus and Intranet/Internet was designed, which was composed of the universal intelligent control nodes (ICNs), the visual control and supervision configuration platforms (VCCP and VSCP) and an Intranet/Internet-based remote supervision platform (RSP). The ICNs were connected to field devices, such as sensors, actuators and controllers. The VCCP and VSCP were implemented by means of a graphical programming environment and network management so as to simplify the tasks of programming and maintaining the ICNs. The RSP was employed to perform the remote supervision function, which was based on a three-layer browser/server(B/S) structure mode. The validity of the NCSS was demonstrated by laboratory experiments.
TL;DR: RScan is a preferable choice for real-life application of searching structural similarities for structured RNAs in large databases and can handle large database queries, taking less than 4 minutes for searching similar structures for a microRNA precursor in human chromosome 21.
Abstract: Many RNAs have evolutionarily conserved secondary structures instead of primary sequences. Recently, there are an increasing number of methods being developed with focus on the structural alignments for finding conserved secondary structures as well as common structural motifs in pair-wise or multiple sequences. A challenging task is to search similar structures quickly for structured RNA sequences in large genomic databases since existing methods are too slow to be used in large databases. An implementation of a fast structural alignment algorithm, RScan, is proposed to fulfill the task. RScan is developed by levering the advantages of both hashing algorithms and local alignment algorithms. In our experiment, on the average, the times for searching a tRNA and an rRNA in the randomized A. pernix genome are only 256 seconds and 832 seconds respectively by using RScan, but need 3,178 seconds and 8,951 seconds respectively by using an existing method RSEARCH. Remarkably, RScan can handle large database queries, taking less than 4 minutes for searching similar structures for a microRNA precursor in human chromosome 21. These results indicate that RScan is a preferable choice for real-life application of searching structural similarities for structured RNAs in large databases. RScan software is freely available at http://bioinfo.au.tsinghua.edu.cn/member/cxue/rscan/RScan.htm
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15 Apr 2007
TL;DR: While the simulation package can get the signal plan from TRANSyT, the TRANSYT models can be visualised in the simulation packages and be developed further.
Abstract: Micro-simulation based traffic models such as VISSIM and Paramics are becoming increasingly popular for the development and evaluation of a broad range of road traffic management and control proposals in recent years. However, in finding the optimised signal plans for networked signals, empirical traffic models such as TRANSYT and LINSIG are still the packages to rely on. In the day to day work of modelling road traffic network, it is highly desirable that these two packages can communicate with each other. While the simulation package can get the signal plan from TRANSYT, the TRANSYT models can be visualised in the simulation packages and be developed further.
01 May 2007
TL;DR: A control scheme based on predictive control is proposed to address the problems introduced by the network, able to avoid the synchronization issue by modelling the predictive controller as an event-driven element.
Abstract: Networked non-linear control systems (NNCS) are studied in this paper. A control scheme based on predictive control is proposed to address the problems introduced by the network. Based on the theory of the linearization of the non-linear process, a predictive control algorithm is constructed to generate a sequence of control predictions, some of which can suitably be selected to control the non-linear process and further compensate for the time delay. Methods are proposed to deal with the selection of control predictions, the control prediction sequence updating, and data disorders processing. The proposed control scheme is able to avoid the synchronization issue by modelling the predictive controller as an event-driven element. The stability of this NNCS has been studied by discussing the stability of an augmented system, the stability conditions of which can be transformed into a series of inequalities. In addition, the control method is validated by both simulations and experiments.
15 Apr 2007
TL;DR: A novel approach is proposed for a networked control system with random delays containing a nonlinear process based on a Hammerstein model which uses a time delay two step generalized predictive control (TDTSGPC), which consists of two parts.
Abstract: A novel approach is proposed for a networked control system with random delays containing a nonlinear process based on a Hammerstein model. The method uses a time delay two step generalized predictive control (TDTSGPC), which consists of two parts, one is to deal with the input nonlinearity of the Hammerstein model and the other is to compensate the network induced delays in the networked control system. Theoretical results using the Popov theorem are presented for the closed-loop stability of the system in the case of a constant delay. Simulation examples illustrating the validity of the approach are presented.
02 Jul 2007
TL;DR: In this article, a real-time simplified variable universe fuzzy control method was proposed for PEM fuel cell flow systems, which can achieve fine control on the cathode pressure of fuel cell stacks by adjusting the input and output universes.
Abstract: The problem of building an accurate model and the request of real-time control are often simultaneously encountered in the design of control systems. This paper successfully studies and implements a real-time simplified variable universe fuzzy control method in PEM fuel cell flow systems. On the one hand, the method can achieve fine control on the cathode pressure of fuel cell stacks by adjusting the input and output universes. On the other hand, the method can also achieve real-time control by activating at most four control rules, at a time, in the inference process for dual-inputs controller. The experimental results at an idle load and a given load demonstrate good performance of this method. The method can also be used in other similar situations.
03 May 2007
TL;DR: In this article, a robust adaptive control of induction motor based on input-output linearization and perturbation estimation is proposed, which can guarantee bounded track errors for bounded time-varying perturbations and achieve asymptotic track when the uncertain parameters converge to unknown constants.
Abstract: This paper investigates a novel robust adaptive control of induction motor based on input-output linearization and perturbation estimation. After representing induction motor as two interconnected subsystems, the lumped term of all nonlinearities, uncertainties and interaction between subsystems are defined as system perturbations and estimated by high-gain perturbation observer. The estimates are employed to achieve the decoupling and robust adaptive linearizing control of flux/speed dynamics. The proposed control can deal with time-varying uncertainties and doesn't require the detailed model of the induction motor. It can guarantee bounded track errors for bounded time-varying perturbations and achieve asymptotical track when the uncertain parameters converge to unknown constants. The performance of the proposed controller is verified by simulation studies.