Showing papers on "Smith predictor published in 2003"

Neural-network predictive control for nonlinear dynamic systems with time-delay

Abstract: A new recurrent neural-network predictive feedback control structure for a class of uncertain nonlinear dynamic time-delay systems in canonical form is developed and analyzed. The dynamic system has constant input and feedback time delays due to a communications channel. The proposed control structure consists of a linearized subsystem local to the controlled plant and a remote predictive controller located at the master command station. In the local linearized subsystem, a recurrent neural network with on-line weight tuning algorithm is employed to approximate the dynamics of the time-delay-free nonlinear plant. No linearity in the unknown parameters is required. No preliminary off-line weight learning is needed. The remote controller is a modified Smith predictor that provides prediction and maintains the desired tracking performance; an extra robustifying term is needed to guarantee stability. Rigorous stability proofs are given using Lyapunov analysis. The result is an adaptive neural net compensation scheme for unknown nonlinear systems with time delays. A simulation example is provided to demonstrate the effectiveness of the proposed control strategy.

Robust Tracking Control of a Piezoactuator Using a New Approximate Hysteresis Model

Abstract: A new approximate model, which consists of a variable gain and a variable time-delay, is proposed to describe the hysteresis behavior of a piezoactuator. The variable gain is assumed to be a function of the magnitude of the input command, while the time-delay is assumed to be a function of the frequency of the input command. The ranges of these two variable parameters are determined through open loop tests. According to the proposed approximate model, a Smith predictor-based robust H x controller is developed to achieve high-precision tracking control of a piezoactuator. Analytical simulation and experimental results on tracking several types of reference inputs demonstrate that the maximum trucking error can be reduced to be less than 2% of the traveling path by utilising the proposed controller design.

On the delay sensitivity of Smith Predictors

Abstract: It is well known that the stability of the Smith Predictor control scheme is sensitive with respect to delay uncertainties. We analysed the effect of delay mismatches on the closed-loop stability and derived various stability/instability characterizations. Thereby, it was assumed that the desired closed-loop transfer function was proper but not necessarily strictly proper. This may induce a sensitivity of stability with respect to infinitesimal delay mismatches and make the scheme practically unstable. We explained the instability mechanism and derived the necessary and sufficient robustness conditions using two different approaches. Under the assumption of practical stability, we then characterized the maximal delay mismatch such that stability was maintained and discussed a numerical example. Both SISO and MIMO systems are considered.

Smith predictor control and internal model control - a tutorial

Abstract: This paper is to provide a guide to the time-delay compensation scheme known as Smith predictor control which uses feedback loop for controlling any system. The Smith predictor control was devised to remove the delay effect from the closed-loop design, and is equivalent to IMC in the sense that the delayed behavior of the plant is cancelled by the plant model. The internal model control (IMC) scheme is discussed together to understand the Smith predictor control in terms of newer theoretical concepts. Related topics such as disturbance rejection, /spl Hscr//sub 2/ optimality, stability, robustness, MIMO systems, SISO systems and windup problem are also discussed.

A new Smith predictor and controller for control of processes with long dead time.

Abstract: Good control of processes with long dead time is often achieved using a Smith predictor configuration. Typically a PI or PID controller is used; however, it is shown in this paper that for some situations improved set point and disturbance responses can be obtained if a PI-PD controller is used. Several methods are possible for selecting the parameters of the PI-PD controller but when the plant transfer function has no zeros, the use of the standard forms provides a simple algebraic approach, and also reveals why difficulties may be encountered if a PID controller is used. Some examples are given to show the value of the approach presented.

A modified Smith predictor for a process with an integrator and long dead time

Abstract: 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.

Autotuning of a new PI-PD Smith predictor based on time domain specifications.

Abstract: The paper extends a recent work on a modified PI-PD Smith predictor, which leads to significant improvements in the control of processes with large time constants or an integrator or unstable plant transfer functions plus long dead time for reference inputs and disturbance rejections. Processes with high orders or long time delays are modeled with lower order plant transfer functions with longer time delays. The PI-PD controller is designed so that the delay-free part of the system output will follow the response of a first-order plant or second-order plant, where it is appropriate, assuming a perfect matching between the actual plant and model in both the dynamics and time delay. The provided simple tuning formulas have physically meaningful parameters. Plant model transfer functions and controller settings are identified based on exact analysis from a single relay feedback test using the peak amplitude and frequency of the process output. Examples are given to illustrate the simplicity and superiority of the proposed method compared with some existing ones.

Performance improvement of smith predictor through automatic computation of dead time

Abstract: It is known that the classical tuning formula for typical ProportionalIntegral-Derivative (PID) controllers in general provides unsatisfactory results for industrial plants where the time delay exceeds the dominant lag time. For this reason, alternative strategies have been studied in order to cope with this problem and, in this context, the most popular scheme is the Smith Predictor. In this paper the theory behind this algorithm is explained and its implementation through YS170 controller language and CENTUM CS3000 Control Drawing Builder are presented in order to verify their effectiveness in industrial environments. This approach requires a good model of the process under control. In fact, the performance of the Smith Predictor can decrease dramatically (become unstable) due to modelling errors, especially for the dead time which, contrary to what would be expected, can vary considerably depending on the working conditions (i.e. the fluid flow). In this paper a simple adaptive law for the automatic tuning of the model time delay is suggested. When this method is applied, the performance of the Smith Predictor is easily improved due to the automatically tuned model dead time and the control algorithm is capable of meeting variable working conditions.

2DOF controller parametrization for systems with a single I/O delay

Abstract: This note puts forward a parametrization of all stabilizing two-degrees-of-freedom controllers for (possibly unstable) processes with dead-time. The proposed parametrization is based on a doubly coprime factorization of the plant and takes the form of a generalized Smith predictor (dead-time compensator) feedback part and a finite-dimensional feedforward part (prefilter). Some alternative dead-time compensation schemes and disturbance attenuation limitations are also discussed.

A new boundary control method for beam equation with delayed boundary measurement using modified Smith predictors

Abstract: The Smith predictor and its variants are applied to the boundary control of Euler-Bernoulli beam equation with delayed boundary measurement to solve the well-known instability problem due to a small time delay. Simulation results demonstrate the effectiveness of the proposed method.

Optimal linear filtering over observations with multiple delays

Abstract: In this paper, the optimal filtering problem for a linear system over observations with multiple delays is treated proceeding from the general expression for the stochastic Ito differential of the optimal estimate and its variance. As a result, the optimal filtering equations similar to the traditional Kalman-Bucy ones are obtained in the form dual to the Smith predictor, commonly used for robust control design in time delay systems. In the example, the obtained optimal filter over observations with multiple delays is verified for a sample system and compared with the best Kalman-Bucy filter available for delayed measurements.

Transparent telemanipulation in the presence of time delay

Abstract: This paper presents a method for providing stability and robust transparency in bilateral teleoperator loops that include a time delay in the communication channel. Specifically, the proposed approach incorporates an adaptive Smith predictor within a frequency domain loop shaping approach that addresses both stability and transparency of the teleoperator loop. Experimental results are presented that demonstrate the effectiveness of the approach.

Behavior of Smith predictor in teleoperation systems with modeling and delay time errors

Abstract: In this paper, behavior of teleoperation systems with modeling error and error of delay time in Smith predictor is discussed. In teleoperation systems usually there is a large distance between master system and slave system. In this case, there is always an error in modeling of system. The condition for stability of teleoperation systems with modeling error is derived by introducing a theorem. This theorem can assist a designer in ensuring the stability of the teleoperation system. Also, error of delay time and stability of teleoperation systems by using of Internet as communication channel are discussed. The effect of delay time prediction on the system stability and performance is studied and it is shown that delay time prediction could improve system performance. Simulation results are presented to verify the obtained results.

An adaptive fuzzy Smith control of time-varying processes with dominant and variable delay

Abstract: An adaptive fuzzy Smith control method is proposed in this paper to control time-varying processes with dominant and variable time delay. By minimizing the error between the process output and the process model output, the variable delay parameter is identified. Based on the on-line parameter estimation, a new Smith predictor is obtained which can compensate for the effect of time delay completely. This method can alleviate the inherent drawback of Smith predictor that its control performance is sensitive to the process model. Furthermore, an adaptive fuzzy controller which can adjust on-line the scaling factors is also incorporated to improve the control performance. Simulation results have demonstrated the effectiveness of the proposed approach.

Model following PID control system

Abstract: The paper deals with robustness to plant parameter perturbations and sensitivity to disturbances of two‐loop control structures containing a model of the controlled plant and two PID controllers. Special attention is paid to high robustness of considered structure to perturbations of the controlled plant in relation to its nominal model and to good reduction of disturbances. On the basis of presented simulation results one can compare properties of the proposed structure with properties of the Smith predictor and classic control system structure with single feedback loop. The proposed model following control structures may find wide application to robust control of parameter‐varying plants.

A new modified Smith predictor design

Abstract: A new modified Smith predictor structure is presented with its associated tuning rules.

Simultaneous adaptive decoupling and model matching control of a fluidized bed combustor for sewage sludge

Abstract: The major difficulties in designing a controller for the fluidized bed combustor for sewage sludge result from the following reasons: 1) The dynamical behavior of the plant is highly unknown and the experimental data only render a coarse model; 2) the combustion process shows large time-delay; and 3) the plant model is a stiff differential equation because the parameter values among the subsystems differ severely. To circumvent these difficulties, this paper proposes to describe each channel of the multiple-input-multiple-output system by a first-order transfer function with variable coefficients and a fixed time delay. A model reference adaptive control scheme, which can simultaneously achieve adaptive decoupling and model matching, is proposed. The resulting adaptive control law guarantees closed-loop stability. The newly obtained controller has a structure that is similar to the well-known Smith predictor. This explains why the present scheme can cope with the time delay effects on the system performance. Due to its adaptation abilities, it can lower the limitations of the Smith scheme to accurate plant descriptions. The application study demonstrates that the proposed design can reach the desired performance requirements.

Quantifying bounded rationality: Managerial behaviour and the Smith predictor

Abstract: The concept of bounded rationality in decision-making and research on its relation to aggregate system dynamics is briefly recalled By recasting the well-known beer game as a Smith predictor control system, a natural measure of the level of bounded rationality in the decision-making process is derived The results herein do accord with those of the original beer game paper In addition, they engender a new interpretation of an important model parameter as a direct measure of the level of bounded rationality inherent in decision-making A stability analysis is then employed to support and qualify the assertion that the level of bounded rationality can adversely affect the aggregate dynamic behaviour of such supply chains The analytical basis of these calculations enables the quantification of the potential cost improvements resulting from more desirable supply-chain dynamics These follow from reduced volatility through improved decision-making in the supply chain This approach is designed to inform the

Robust prediction-based control for unstable delay systems

Abstract: We present a discrete-time prediction based state-feedback controller. It is shown that this controller stabilizes possibly unstable continuous-time delay systems. The stability is shown to be robust with respect to uncertainties in the knowledge on the plant parameters, the system delay and the sampling period. The proposed prediction based controller has been tested in a real-time application to control the yaw angular displacement of a 4-rotor mini-helicopter.

Teleoperations over an IP network : virtual PUMA robot

Abstract: We present a stable remote position/force control scheme for manipulator robot via Internet based on Smith predictor principle To validate this control method, we developed a real time Virtual Puma robot based on RT-linux operating system This virtual robot contains a real time task which computes the differential non linear equation of the PUMA robot including a virtual environment in order to perform a force control loop Some interesting experiments in the case of long distance (Mexico-France: /spl sim/8000 km) show the real improvement obtained by this method with a long mean time delay (/spl sim/250ms) This addition enhances and secures the teleoperation through the internet

An outline and further development of Smith predictor based methods for the compensation of processes with time delay

Abstract: An extensive literature review is presented and a new modified Smith predictor structure is subsequently presented.

Tuning of a modified Smith predictor for processes with time delay

Abstract: A modified Smith predictor proposed in Majhi and Atherto (1999) is shown to be equivalent to a modified internal model control (IMC) structure, and then a three stage design method is proposed for the Smith predictor To achieve compromise between disturbance rejection and stability robustness, a robust control method is used to tune the feedback loop controller Design for some typical integrating and unstable processes with time delay shows that the proposed method can achieve good compromise between setpoint tracking, disturbance rejection and stability robustness

Smith predictor based neural fuzzy controller applied in a water gas heater that presents a large time-delay and load disturbances

Abstract: This paper presents a work in progress concerning the use of neuro-fuzzy based non-linear Smith predictor for control a real system with a large and variant time delay and load disturbances. The main objective is to control the output water temperature of one domestic water gas heater that presents a large time-delay and water flow, cold water temperature and wanted output temperature changes. It is presented a detailed description of the water gas heater in terms of non-linearity, time constants and time delay. The steps taken to arrive at the direct and inverse models using a neuro-fuzzy technique are described. The two control strategies, non-linear Smith predictor controller and an improved non-linear Smith predictor controller, were implemented in the 89C51RD PHILIPS micro-controller and the real time results are presented. The improved non-linear Smith predictor controller consists in a fuzzy compensation of the steady-state errors and a compensation for small variations of the time-delay.

Comparison of several well-known controllers used in process control.

Abstract: In this paper, several well-known design methods, PID control, Smith predictor, inferential control, internal model control, Dahlin controller, deadbeat control, and predictive control, are studied. A suboptimal Smith predictor is derived. The relationship among these methods is investigated. It is shown that these methods are equivalent to each other on certain premises. This explains why they are widely used in process control and provides insight into the work of bringing these techniques together to control system design. Examples are given to illustrate the result.