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Weidong Zhang - One of the best experts on this subject based on the ideXlab platform.
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A ratio control scheme decoupling Disturbance Response from set-point Response
Isa Transactions, 2007Co-Authors: Weidong ZhangAbstract:In this paper a novel ratio control scheme is proposed for stable and unstable processes with time delay. The proposed ratio control system consists of two control loops with two-degrees-of-freedom control structure, which decouples the set-point Response of each loop from its Disturbance Response. Two ratio controllers separately for the set-point and load Disturbance changes are introduced between the two control loops, in order to achieve improved ratio control performance during the transients caused by the set-point and Disturbance changes and to decouple the set-point Response of the whole ratio control system from its Disturbance Response. For easy understanding and tuning, all the controllers in the ratio control system are designed analytically. As a result, the set-point and load Disturbance Responses of the ratio control system can be independently and conveniently tuned by a single control parameter. In addition, the proposed ratio control scheme can provide quantitative performance estimation. Simulation examples are included to illustrate the effectiveness of the proposed method.
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Analytical two-degree-of-freedom design method for linear processes with time delay
2006 American Control Conference, 2006Co-Authors: Linlin Ou, Qizhi Zhang, Weidong ZhangAbstract:In this paper, an analytical two-degree-of-freedom control method is proposed for linear systems with time delay, including stable, unstable and nonminimum-phase plants of arbitrary order. The reference models for setpoint Response and Disturbance Response are first presented, respectively, by virtue of dynamical characteristic of the control system and internal stability conditions. Then, the controllers are derived inversely. The resulting ideal controller for Disturbance rejection is involved with time delay in a complex manner, and thus, the analytical controller reduction formulas are provided to reproduce it in the PID form by employing the Maclaurin expansion. This brings much convenience to the controller implementation. Moreover, quantitative performance and robust stability of the control system are discussed. The setpoint Response and Disturbance Response can be separately regulated by tuning the corresponding control parameters. Finally, Simulation examples are included to show the effectiveness of the proposed method
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analytical design of two degree of freedom control scheme for open loop unstable processes with time delay
Journal of Process Control, 2005Co-Authors: Weidong Zhang, Danying GuAbstract:Abstract This paper proposes an analytical two-degree-of-freedom control scheme for open-loop unstable processes with time delay, which leads to the remarkable improvement of regulatory capacity for both of reference input tracking and load Disturbance rejection. Firstly a conventional proportional or plus derivative controller is deliberately employed for stabilizing the setpoint Response. Then the setpoint tracking controller is analytically derived in terms of the integral-squared-error (ISE) performance specification. By proposing the desired closed-loop complementary sensitivity function for rejecting load Disturbances, the corresponding controller, i.e. Disturbance estimator, is inversely figured out. Hence the nominal setpoint Response is decoupled from the load Disturbance Response by virtue of the open-loop control manner for the setpoint tracking. In consequence, both of them can be optimized simultaneously and separately. At the same time, robust stability analysis for the proposed control structure is provided in the presence of the process multiplicative uncertainty. Accordingly the on-line tuning rule for the single adjustable parameter of each controller is suggested to cope with the process unmodeled dynamics in practice. Finally, several illustrative examples are included to demonstrate the superiority of the proposed method.
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new modified smith predictor scheme for integrating and unstable processes with time delay
IEE Proceedings - Control Theory and Applications, 2005Co-Authors: Danying Gu, Weidong ZhangAbstract:The paper extends a recently published Smith predictor scheme for controlling integrating and unstable processes with time delay, which results in a simpler control structure and improved tuning capacities for reference inputs and load Disturbances. In the proposed scheme, a proportional controller is subtly employed to stabilise the setpoint Response, and then an H2 optimal controller is analytically designed for setpoint tracking. To obtain the integral-squared-error (ISE) performance objective, a practically desired Disturbance rejection transfer function is proposed to design the Disturbance estimator in the inner closed loop of the proposed control structure. Essentially, the proposed control structure gives two-degrees-of-freedom (2DOF) control and correspondingly the setpoint and load Disturbance Responses can each be tuned conveniently by a single control parameter. Hence the setpoint Response is decoupled from the load Disturbance Response, and both can be quantitatively estimated in terms of the proposed analytical tuning procedures. Simulation examples are included to show the superiority of the proposed method.
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technical communique two degree of freedom smith predictor for processes with time delay
Automatica, 1998Co-Authors: Weidong Zhang, Xiaoming XuAbstract:In this paper, the conventional Smith predictor is modified, which leads to significant improvements in its regulatory capacities for reference inputs and Disturbances. The proposed modification utilizes the existing prediction of the conventional time delay compensator and decouples the setpoint Response from the Disturbance Response. The setpoint Response and the Disturbance Response of the closed-loop system are adjusted by two parameters, respectively. This allows the designer to optimize them simultaneously. Illustrative examples are provided to show the advantages of the modified scheme.
T.d.a. Forbes - One of the best experts on this subject based on the ideXlab platform.
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Disturbance Response in vegetation – towards a global perspective on functional traits
Journal of Vegetation Science, 1999Co-Authors: Sue Mcintyre, Sandra Lavorel, Jill Landsberg, T.d.a. ForbesAbstract:. Previous work on trait correlation patterns has contributed to the identification of broad patterns of plant distribution along environmental gradients in vegetation. However, these general trends may conceal subtle mechanisms of Response that are specific to particular types of Disturbance. To address this, we propose a generic methodology for the analysis of traits, using herb-dominated vegetation as a model. Hypothetical biological traits are identified for testing against Disturbance gradients. The traits were selected for their perceived relevance to Disturbance Response generally, but also include a specific focus on domestic livestock grazing. The analysis is structured hierarchically to enable attributes to be analysed within major life forms. A different selection of traits is identified as being relevant to each major life form. Flexible adaptation in the use of the trait set is suggested as a way of comparing functional Response to Disturbance over a series of locations. For example, assemblages will vary in their representation of the major life forms, and it may be relevant to analyse traits within a subset of these life-form groups. Because individual studies encompass a limited range of environmental variation, and local floras may be constrained by their evolutionary context, similar approaches need to be tested over a range of vegetation types and geographic situations. A significant advance in functional trait analysis could be achieved if individual studies provide explicit descriptions of their evolutionary and ecological context from a global perspective.
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Disturbance Response in vegetation towards a global perspective on functional traits
Journal of Vegetation Science, 1999Co-Authors: Sue Mcintyre, Sandra Lavorel, Jill Landsberg, T.d.a. ForbesAbstract:. Previous work on trait correlation patterns has contributed to the identification of broad patterns of plant distribution along environmental gradients in vegetation. However, these general trends may conceal subtle mechanisms of Response that are specific to particular types of Disturbance. To address this, we propose a generic methodology for the analysis of traits, using herb-dominated vegetation as a model. Hypothetical biological traits are identified for testing against Disturbance gradients. The traits were selected for their perceived relevance to Disturbance Response generally, but also include a specific focus on domestic livestock grazing. The analysis is structured hierarchically to enable attributes to be analysed within major life forms. A different selection of traits is identified as being relevant to each major life form. Flexible adaptation in the use of the trait set is suggested as a way of comparing functional Response to Disturbance over a series of locations. For example, assemblages will vary in their representation of the major life forms, and it may be relevant to analyse traits within a subset of these life-form groups. Because individual studies encompass a limited range of environmental variation, and local floras may be constrained by their evolutionary context, similar approaches need to be tested over a range of vegetation types and geographic situations. A significant advance in functional trait analysis could be achieved if individual studies provide explicit descriptions of their evolutionary and ecological context from a global perspective.
Danying Gu - One of the best experts on this subject based on the ideXlab platform.
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analytical design of two degree of freedom control scheme for open loop unstable processes with time delay
Journal of Process Control, 2005Co-Authors: Weidong Zhang, Danying GuAbstract:Abstract This paper proposes an analytical two-degree-of-freedom control scheme for open-loop unstable processes with time delay, which leads to the remarkable improvement of regulatory capacity for both of reference input tracking and load Disturbance rejection. Firstly a conventional proportional or plus derivative controller is deliberately employed for stabilizing the setpoint Response. Then the setpoint tracking controller is analytically derived in terms of the integral-squared-error (ISE) performance specification. By proposing the desired closed-loop complementary sensitivity function for rejecting load Disturbances, the corresponding controller, i.e. Disturbance estimator, is inversely figured out. Hence the nominal setpoint Response is decoupled from the load Disturbance Response by virtue of the open-loop control manner for the setpoint tracking. In consequence, both of them can be optimized simultaneously and separately. At the same time, robust stability analysis for the proposed control structure is provided in the presence of the process multiplicative uncertainty. Accordingly the on-line tuning rule for the single adjustable parameter of each controller is suggested to cope with the process unmodeled dynamics in practice. Finally, several illustrative examples are included to demonstrate the superiority of the proposed method.
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new modified smith predictor scheme for integrating and unstable processes with time delay
IEE Proceedings - Control Theory and Applications, 2005Co-Authors: Danying Gu, Weidong ZhangAbstract:The paper extends a recently published Smith predictor scheme for controlling integrating and unstable processes with time delay, which results in a simpler control structure and improved tuning capacities for reference inputs and load Disturbances. In the proposed scheme, a proportional controller is subtly employed to stabilise the setpoint Response, and then an H2 optimal controller is analytically designed for setpoint tracking. To obtain the integral-squared-error (ISE) performance objective, a practically desired Disturbance rejection transfer function is proposed to design the Disturbance estimator in the inner closed loop of the proposed control structure. Essentially, the proposed control structure gives two-degrees-of-freedom (2DOF) control and correspondingly the setpoint and load Disturbance Responses can each be tuned conveniently by a single control parameter. Hence the setpoint Response is decoupled from the load Disturbance Response, and both can be quantitatively estimated in terms of the proposed analytical tuning procedures. Simulation examples are included to show the superiority of the proposed method.
Qing-guo Wang - One of the best experts on this subject based on the ideXlab platform.
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Identification of Hammerstein systems with time delay under load Disturbance
Iet Control Theory and Applications, 2018Co-Authors: Shijian Dong, Tao Liu, Qing-guo WangAbstract:To cope with load Disturbance often encountered when performing identification tests on non-linear systems with input delay in industrial applications, a bias-eliminated Hammerstein-type output error (OE) model identification method is proposed in this study. By taking into account the load Disturbance Response as a time-varying parameter for estimation, two recursive least-squares (RLS) identification algorithms is established to estimate the Hammerstein-type model parameters and the time-varying Disturbance Response. A one-dimensional searching approach is adopted to determine the integer-type delay parameter by minimising the fitting error of output Response. Moreover, an auxiliary OE model is constructed to ensure consistent estimation under stochastic noise. In addition, two adaptive forgetting factors are introduced into the proposed RLS algorithms to enhance the estimation convergence on the model parameters and the Disturbance Response. Asymptotic properties of parameter estimation are analysed along with a proof, in particular for unbiased estimation against a constant Disturbance. Two illustrative examples are given to demonstrate the effectiveness of the proposed identification method.
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Identification of dual-rate sampled systems with time delay subject to load Disturbance
Iet Control Theory and Applications, 2017Co-Authors: Shijian Dong, Tao Liu, Qing-guo WangAbstract:A discrete-time model identification method is proposed for dual-rate sampled systems with time delay subject to load Disturbance with unknown dynamics. By viewing the output Response arising from such load Disturbance as a dynamic parameter for estimation, two recursive least-squares identification algorithms are developed to estimate the linear model parameters and the load Disturbance Response, respectively, while the integer delay parameter is derived by using a one-dimensional searching approach to minimise the output fitting error. An auxiliary model is constructed to estimate the unknown noise-free output such that consistent estimation of the model parameters can be obtained under stochastic noise in the output measurement. Moreover, two adaptive forgetting factors are introduced to expedite the convergence rates of estimating the model parameters and the load Disturbance Response, respectively. Theoretical analysis is given to clarify the convergence of parameter estimation. Two illustrative examples are presented to demonstrate the effectiveness and merit of the proposed identification method.
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Recursive subspace identification subject to relatively slow time-varying load Disturbance
International Journal of Control, 2017Co-Authors: Jie Hou, Tao Liu, Qing-guo WangAbstract:ABSTRACTIn this paper, a recursive subspace identification method is proposed to identify linear time-invariant systems subject to load Disturbance with relatively slow dynamics. Using the linear superposition principle, the load Disturbance Response is decomposed from the deterministic-stochastic system Response in the form of a time-varying parameter. To ensure unbiased estimation of the deterministic system matrices, a recursive least-squares (RLS) identification algorithm is established with a fixed forgetting factor, while another RLS algorithm with an adaptive forgetting factor is constructed based on the output prediction error to quickly track the time-varying parameter of load Disturbance Response. By introducing a deadbeat observer to represent the deterministic system Response, two extended observer Markov parameter matrices are constructed for recursive estimation. Consequently, the deterministic matrices are retrieved from the identified system Markov parameter matrices. The convergence of th...
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a modified smith predictor for a process with an integrator and long dead time
Industrial & Engineering Chemistry Research, 2003Co-Authors: C C Hang, Qing-guo Wang, Xueping YangAbstract:In this paper, a new modified Smith predictor using a rapid load estimator scheme is proposed. The advantage of the design is that the load estimator does not involve the solution of a closed-loop equation that contains dead time, and this can achieve a better load Disturbance Response. This scheme can be easily extended to the case of double integrators. Robust stability of the proposed method is analyzed, and a simple and effective robust controller design rule is derived. It is demonstrated by simulations that the new controller provides a similar or better setpoint Response and a faster load Disturbance rejection than the dead-time compensator in other papers.
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Continual Self-Tuning from Load Disturbance Responses
Chemical Engineering Research & Design, 1998Co-Authors: Qing-guo Wang, Chang Chieh HangAbstract:In this paper, a new continual self-tuning control scheme based on an unknown process Response under load Disturbance is proposed. It can re-estimate the possibly changed process frequency Response using the benign process transients under an unknown step or impulse, like load Disturbance. According to the Disturbance Response pattern, the unknown step/impulse like load Disturbance is assumed to be generated by passing a step or an impulse through unknown rational function dynamics. With process input and output frequency Response computed by FFT, the best estimation of the process frequency Response is obtained using the least squares method. Based on the re-estimated process frequency Response, a PID controller is re-tuned to adapt to the possible changes in the process. The effectiveness of the method is demonstrated through simulation examples and real-time tests.
Xiaoming Xu - One of the best experts on this subject based on the ideXlab platform.
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technical communique two degree of freedom smith predictor for processes with time delay
Automatica, 1998Co-Authors: Weidong Zhang, Xiaoming XuAbstract:In this paper, the conventional Smith predictor is modified, which leads to significant improvements in its regulatory capacities for reference inputs and Disturbances. The proposed modification utilizes the existing prediction of the conventional time delay compensator and decouples the setpoint Response from the Disturbance Response. The setpoint Response and the Disturbance Response of the closed-loop system are adjusted by two parameters, respectively. This allows the designer to optimize them simultaneously. Illustrative examples are provided to show the advantages of the modified scheme.