A comparison of the Smith predictor and conventional feedback control

Meyer, Christoph; Seborg, Dale E.; Wood, R. K.

doi:10.1016/0009-2509(76)80050-4

Cited by 49 publications

(15 citation statements)

References 8 publications

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“…)) dead-time compensator (DTC) in the control scheme. Many simulation and experimental studies (Lupfer and Oglesby, 1962;Buckley, 1960;Nielsen, 1969;Garland and Marshall, 1974;Meyer et d . , 1976;ROSS, 1977;Alevisakis and Seborg, 1974;Ioannides et a]., 1979, for example) have demonstrated the potential improvement of the DTC over conventional controllers.…”

Section: Introductionmentioning

confidence: 99%

Improved dead‐time compensator controllers

Palmor

Powers²

1985

AIChE Journal

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It is shown that the conventional Smith dead-time compensator can be modified in a fashion which leads to significant improvements in its regulatory capabilities for measurable disturbances or inputs. The proposed modification utilizes effectively the existing prediction capabilities of the conventional dead-time compensator and eliminates the need for a separate feedforward controller in many circumstances under which it is normally employed. The modified dead-time compensator possesses simultaneous feedforward and feedback actions. An additional tuning parameter which controls the degree of dead-time cancellation allows the designer to shape the response according to requirements. Illustrative examples show the advantages of the modified scheme. SCOPEA long-standing problem in process control is that of controlling processes with significant deadtimes between inputs and outputs. A considerable improvement in the control in these cases may be obtained via the 0. J. M. Smith dead-time compensator (DTC) which recently has been extended to systems with multiple dead times. While the inclusion of the DTC considerably improves the performance of the controlled loop for setpoint changes, as has been shown by numerous experimental and simulation studies, the enhancements in disturbance rejection capabilities are not as apparent.This paper reveals the reason for this and presents a simple, yet novel, modification of the DTC. With this modification, the dead time of the system to measurable disturbances is also compensated. This leads to significant improvements in the regulation capabilities of the DTC while retaining all its other properties. By treating the degree of compensation as a design parameter, it is shown that the overall performance may be further improved in certain cases. Analytical approach to the determination of the degree of compensation is also discussed.The main features of the new design are demonstrated through simulated responses. CONCLUSIONS AND SIGNIFICANCEThe servomechanism properties of process controllers are considerably improved by the inclusion of a conventional dead-time compensator. DTC-based controllers traditionally have been considered and treated as feedback-only control schemes, and therefore no attention has been paid to the possibility of extending their properties to those of feedforward controllers. The modified DTC proposed in this paper utilizes the existing process model contained in the conventional DTC to predict the effect of the disturbances on the outputs. These predictions are further used in the new DTC to cancel the long dead times that usually exist between the disturbance and its effect on the output. Consequently, the control actions taken AlChE Journal (Vol. 31, No. 2) counteract the effect of the disturbances before they can appreciably change the output. In this fashion, the conventional DTC is extended to encompass features of feedforward controllers without the employment of separate controllers. This leads to significant improvements in the regulation propert...

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Section: Introductionmentioning

confidence: 99%

Improved dead‐time compensator controllers

Palmor

Powers²

1985

AIChE Journal

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“…The applicability of the Smith predictor, especially compared to the PID controller, has been examined [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]; Seborg et al [9], for instance, quote studies stating that the Smith predictor performance for servo applications is up to 30% better than the use of an appropriately tuned PID controller.…”

Section: The Smith Predictormentioning

confidence: 99%

A reference guide to Smith predictor based methods for the compensation of dead-time processes

O’Dwyer¹

2005

IEE Irish Signals and Systems Conference 2005

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“…What's more, the dynamics of this temperature loop is complex with large time delay, which poses challenges for traditional PID control [6][7][8][9][10][11][12]. The uncertainties in this process also add to the difficulty for PID control to achieve satisfactory performance [13,14].…”

Section: Introductionmentioning

confidence: 97%