Showing papers on "Smith predictor published in 1999"

On the modified Smith predictor for controlling a process with an integrator and long dead-time

Abstract: A dead-time compensator for controlling higher-order processes with integral action and long dead-time is proposed. Tuning formulas are derived. If the velocity gain and the dead-time are estimated experimentally, only one parameter, the time constant defining the speed of the closed-loop setpoint response, has to be tuned manually. The same setpoint response is obtained as in the modified Smith predictor, while the load disturbance rejection is considerably faster.

Modified Smith predictor and controller for processes with time delay

Abstract: A modified Smith predictor and a simple but very effective controller design procedure is proposed for time delay processes. The controller has a simple structure whose high performance particularly for unstable and integrating process is clearly shown. Design of the controllers is based on standard forms of the closed-loop system response with a variable zero and on the optimum stability approach of De Paor and O'Malley (1989) for a proportional controller for an unstable process. Illustrative examples show the superiority of the proposed controller design method over previously published approaches in terms of both closed-loop performance and robustness.

A modified Smith predictor with a new structure for unstable processes

Abstract: In this paper, we propose a modified Smith predictor with a new structure for unstable processes. The proposed new structure makes it possible to use the unstable model itself as a process model, w...

Robustness effects of a prefilter in a Smith predictor-based generalised predictive controller

Abstract: The paper describes how to increase the robustness of the Smith predictor-based generalised predictive controller while maintaining a nominal performance. The design of filters to improve robustness has several advantages: it is much simpler than the normal procedure used in generalised predictive controllers; it allows for better robustness indices than the optimal predictor-based GPC with the same order of filter; and it maintains the same reference to output nominal performance for every choice of filter. To illustrate the properties of the filtered Smith predictor-based generalised predictive controller some examples, taken from recent papers, are presented.

Smith predictor and modifications: A comparative study

Abstract: This paper analyzes the performance and robustness of some of the structures of dead-time compensators that have been proposed in literature. The analysis is made using the two most typical models of processes with delay that are found in the process industry. All the structures are compared to a simple two degree of freedom Smith predictor. The comparative analysis shows that for the cases studied this simple structure gives the same performance as the others. Also it is shown that the tuning of this structure is simple because the tuning parameters have the usual physical meaning. Some simulation examples illustrate the results.

Dynamical classes in the minimum time pole assignment control

Abstract: This paper presents new integrated approach to the control design of SISO systems with constrained input. It is based on generalisation of several well approved control concepts: Of the bang-bang” minimum time control [1,4,16,18], of the linear pole assignment control [2,5], of the Smith predictor [18], of the controller tuning corresponding to a double real closed loop pole by Oldenbourg and Sartorius [15] and that of the process reaction curve approximation by Ziegler and Nichols [20]. All these up to now separately treated techniques are integrated into unique approach and shown to represent its special limit solutions. The new concept is built up on introduction of dynamical classes of minimum time pole assignment (MTPA) control, corresponding to the well known Feldbaums theorem [4] about n-interval of optimal control. All possible control structures are classified according to the number of intervals in their control sequences.

On the state prediction of linear systems with time-delays in the input and the state

Abstract: The purpose of the work is the study of the state prediction problem related with a class of single-input single-output linear time-delay systems A modification of the classical Smith predictor scheme is proposed for a large class of time delay systems in the sense that we allow time-delays not only in the input signal but also in the state of the system The proposed compensator provides an approximate estimation of the future value of the state that it is used to solve two common control problems: path tracking and disturbance rejection It is shown that the prediction error converges to zero based on the stability properties of the time-delay system

Automatic tuning of the flexible Smith predictor controller

Abstract: The paper presents an extension of the modified Smith predictor controller referred to as the flexible Smith predictor control scheme. The tuning procedure is based on the multiple integration method and requires only the process open-loop step response to calculate the parameters of the flexible Smith predictor. The desired trade-off between robustness and the closed-loop performance can be achieved by means of only one free parameter.

Robust time-delay control of a reclaimer

Abstract: In this paper, a robust time delay control for a reclaimer is investigated. Supplying the same amount of raw material throughout the reclaimation process, from the raw yard to a sinter plant, is important to keep the quality of the molten steel uniform. As the parameter values of the reclaimer are not available, the boom rotational dynamics. is modeled as a second order differential equation with unknown coefficients. The unknown parameters in the nominal model are estimated using recursive estimation method. Another important factor in the control problem of a reclaimer is the large time delay in output measurement. Assuming a multiplicative uncertainty, that accounts for both the unstructured uncertainty neglected in the modeling and the structured uncertainty in the parameter estimation, a robust Smith predictor is designed. A robust stability criterion for the multiplicative uncertainty is derived. Following the work of Goodwinet al. (1992), a quantifying procedure of the multiplicative uncertainty bound, through experiments, is described. Experimental and simulation results are provided.

Simplifying controller for process control of systems with large dead time

Abstract: Large dead time is a significant control problem and source of instability for the control loop. A Smith Predictor scheme provides a conventional large dead time compensation leaving other process dynamics to the separate controller. The real long dead time processes, such as heat transfer and flow control systems, typically exhibit long time delays intertwined with other process dynamics. One of the authors, Roman Gorecki, proposed and implemented a new algorithm, based on the principle of simplification of the control system transfer function, to deal with this issue. The concept of this new algorithm, called a Simplifying Controller, is briefly presented. It is followed by the real system example where a heat transfer process control system with use of the Simplifying Controller is described. The Simplifying Controller algorithm offers improved control for large dead-time process control applications.

Simple predictor for processes with time delay

Abstract: A method is presented based on optimal control theory for the design of a Smith predictor. The resulting controller has two notable merits. First, explicit formulas are obtained for calculating parameters of the controller. Second, the nominal performance of closed loop system, such as overshoot and rise time, can be evaluated quantitatively. It is found that the proposed Smith predictor can be equivalent to the Dahlin controller and a PID controller. A numerical example is provided to illustrate the method.

An application of time delay estimation by ANNs to frequency domain adaptive I-PD controller

Abstract: We present an auto-tuning method of frequency domain adaptive I-PD controllers using online time delays estimation by ANNs (artificial neural networks). The ANN architecture used is a simple Adaline with the LMS training algorithm. The proposed control scheme applies estimated time delays to the Smith predictor and estimates the frequency response of the controlled object using the sliding DFT. The control gains are then determined so as to minimize the model error between the closed-loop frequency response of desired system and that of the actual system.

Smith predictor for uncertain systems in the QFT framework

Abstract: It is well known that the Smith Predictor Controller SPC may be very sensitive to model-plant mismatch, resulting in a poor performance when model uncertainty is present. This paper introduces two criteria for the design of a SPC when the plant-rational part and time delay- is not precisely known.

Modified Smith predictor for extruded diameter control

Abstract: An overview is given of an adaptive strategy for controlling output dimensions from a plastic-on-wire extrusion process, using gain-scheduled PI control in a Smith predictor control scheme. Process behaviour is most easily understood and predicted by developing a process model, and hence the article details the problem of modelling the extrusion process, with the objective of developing a standardised routine for tuning dimensional control systems. The article describes the model of diameter measurement on a cable extrusion process which was used to provide the basis for further analysis and simulation. Next, three alternative control strategies for the diameter control problem are reviewed and compared, illustrating that a combination of well-proven strategies can give significant performance improvements.

New Approach for Design and Automatic Tuning of the Smith Predictor Controller

Abstract: In this paper, we present a new Smith control design using a deliberate mismatch between the actual process and process model. With this particular representation, every Smith control system has an associated Smith compensated (SC) process that is an interactive function of the actual process and process model. Under this alternative Smith control structure, it is both intuitive and demonstrative by simulation study that the best Smith control design does not necessarily arise from the use of the perfect process model but rather the use of an adequately chosen model that results in the SC process possessing good dynamical properties from the viewpoint of the controller. Thus, the process modeling phase of the Smith control design may be viewed as a process precompensation design, and the final primary controller design will be carried out with respect to the SC process. For ease of practical applications, the entire procedure from modeling to control design may be automated and carried out online, using a new online relay tuning method. Robustness analysis of the new Smith control design is further carried out in the paper by drawing on existing results for single-input-single-output feedback systems. Simulations are provided to illustrate the applicability and effectiveness of both the online autotuning approach and the new Smith control design technique.

Parallel Compensation with a Secondary Measurement

Abstract: A secondary measurement is usually used in the form of cascade control to effectively reject disturbances to the manipulated variable. In the cascade control system, the inner loop is tuned first and then the outer loop is tuned with the inner loop closed. When the dynamics of the inner process is slow, this tuning procedure does not provide the best control performance. Here, for slow inner processes, parallel compensation similar to the Smith predictor and the internal model control is shown to be more effective than the cascade control. A very simple tuning rule and a simple anti-reset windup are feasible in this control structure. It can be used in its own structure or to tune the cascade control system systematically. For automatic tuning of the proposed control system, an identification method which finds two process models with the relay feedback and P-control tests is also proposed.

Reclaimer control: modeling, identification, and a robust Smith predictor

Abstract: In this paper, a robust time delay control for a reclaimer is investigated. Supplying the same amount of raw material throughout the reclaimation process, from the raw yard to a sinter plant, it is important to keep the quality of the molten steel in a blast furnace uniform. Since the parameter values of the reclaimer are not available, the boom rotational dynamics is modeled as a second order differential equation with unknown coefficients. The unknown parameters in the nominal model are estimated using recursive estimation method. Another important factor in the control problem of a reclaimer is the large time delay in output measurement. A robust Smith predictor is designed, and a robust stability criterion for the multiplicative uncertainty is derived. Following the work of Goodwin et al. (1992), a quantifying procedure of the multiplicative uncertainty bound, through experiments, is described. Experimental and simulation results are provided.

A double\|controller scheme for industrial processes with dominant delay

Abstract: A simple and practical double\|controller scheme is proposed for industrial processes with dominant delay.It contains two separate controllers,a set\|point controller and a load controller.The set\|point response of the closed\|loop system is then decoupled from the load response.As a result,the two controllers can be separately designed to obtain good performance in both set\|point tracking and load rejections.The double\|controller scheme is model based.It is,however,insensitive to the process model,resulting in good system robustness.The two controllers are taken to be proportional\|integral(PI)type for simplicity.Tuning procedures of the two controllers are also presented.

Stability of saturated dead-time compensating pi controllers for uncertain dead-time systems

Abstract: This paper analyzes the global stability of a dead-time compensator when considering a saturation in the control action and uncertainties in the estimation of the dead-time. The analysis is made using a first order plant with dead-time controlled by a Smith predictor plus a pi controller, that is, a scheme commonly used in the process industry. Using a frequency domain analysis the stability and the bifurcations of the system are analyzed when a saturation is included in the control system. The obtained results suggests the use of filters to avoid the undesirable effects produced by the error in the estimation of the dead-time and the saturation. The design of these filters is based on the stability analysis performed in this paper and gives less conservative results than the ones obtained using others approaches. In order to illustrate the results, some simulation examples are shown.

Improving vehicle performance using adaptive control techniques

Abstract: This paper reviews a collaborative research programme aimed at improving vehicle performance using adaptive control techniques. Initially the design of active suspension systems is considered, and the benefits of using a non-linear controller model with an adaptive control scheme are discussed. Adaptive schemes for active roll control are then considered, and the merits of incorporating a Smith predictor to accommodate for system delays are high-lighted. Preliminary research in adaptive cruise control and collision avoidance is discussed and plans for further developments are outlined.

Linear time delay systems : (LTDS '98) : a proceedings volume from the IFAC Workshop, Grenoble, France, 6-7 July 1998

Abstract: Chapter headings and selected papers: Robust Stabilization. Robust stabilizing control for uncertain time-delay systems containing saturating actuators (H. Su, J. Chu). Structural Properties. On equivalence at infinity and row-by-row decoupling for linear systems with delays (R. Rabah). Multiple Delay Systems. Numerical computation of cross-covariance functionals for linear systems with multiple time delays (J.-H. Hwang et al.). H2H . Quadratic cost control of dynamical systems with a discrete delayed control (L. Chraibi et al.). Stability and Stabilization of Linear Time Delay Systems. Mixed delay-independent / delay-dependent stability of linear systems with delayed state: an L.M.I. approach (S.-I. Niculescu et al.). Application: Case Study. A case study on balanced reduction of time delay systems (T. Izumi et al.). Algebraic, Structural and Geometric Approaches for Ring Models of Time-Delay Systems. Feedback stabilization over communicative rings using homogeneous images (K. Mori, K. Abe). Dead Beat. Dead-time compensators: a unified approach (J.E. Normey-Rico, E.F. Camacho). Stability Analysis. An extension of lucas theorem to entire functions (J. Moreno). Stabilization. Stabilizing rational controllers for a class of a time-delay systems (L. Naimark et al.). Robust Stability. Method of difference transformations for differential systems with linear time-delay (A.A. Laktionov, A.P. Zhabko). Smith Predictor. Quasi-finite linear delay systems: theory and applications (M. Fliess, H. Mounier). Plenary Papers. Algebraic tools for the control and stabilization of time-delay systems (J.J. Loiseau). Author index.

Robust controller design for time delay systems using H-infinity techniques

Abstract: Using H∞ control, the design problem is formulated in terms of user defined weighting polynomials on the process closed-loop Sensitivity functions to achieve desired closed-loop performance and robust stability in the presence of process modelling error. In this paper stability conditions , in terms of the process sensitivity functions, are derived for processes containing a pure time delay for the following three design scenarios i) the time delay is neglected in the control design and is considered as part of the unmodelled process dynamics ii) A Pade approximation of the delay is included in the controller design and the effect of the residual time-delay modelling error on stability is considered iii) stability conditions for time delay mismatch using the Smith Predictor are derived.