A simple method of designing the controllers for a modified form of Smith predictor is proposed for integrating and double integrating processes with time delay. The modified Smith predictor has two controllers, namely, a set point tracking controller and a load disturbance rejection controller for obtaining good set point tracking and load disturbance rejection, respectively. The set point tracking controller is designed using the classical direct synthesis method based on the process model without considering the time delay. The disturbance rejection controller is considered as a proportional-derivative (PD) controller and is designed using optimal gain and phase margin approaches. Set point weighting is considered for reducing undesirable overshoots and settling times in the modified Smith predictor. Guidelines are provided for selection of the desired closed loop tuning parameter in the direct synthesis method and the set point weighting parameter. The method gives significant load disturbance rejection performances. Illustrative examples are considered to show the performances of the proposed method. A significant improvement in control performance is obtained when compared to recently reported methods. © 2006 ISA.

Vadarevu S.Ramachandra Rao

Manickam Chidambaram

Control equipment

Electronic circuit tracking

Phase measurement

Proportional control systems

Time measurement

DIRECT SYNTHESIS METHOD

INTEGRATING PROCESS

SET POINT WEIGHTING

SMITH PREDICTOR

Time delay

Predictive control systems

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IIT Madras

ISA Transactions

In this chapter, methods for designing PI/PID controllers for integrating and unstable systems are summarized. Several examples of unstable and integrating processes are provided. A review on controller design methods, based on the direct synthesis method, IMC method, and equating coefficient method, is presented. Further, methods of calculating the set-point weighting parameter are given. Robust analysis is carried out using Small gain theorem and Kharitonov’s theorem. Simulation results are given on few case studies. © 2012, Springer-Verlag London Limited.

Advances in Industrial Control

PI/PID controllers design for integrating and unstable systems

A process having any pole at origin is said to be integrating in nature. In practice, it is difficult to obtain the desired output from such integrating processes with significant time delay. Pure integrating processes have inherent non self-regulating feature and hence if they are disturbed from their equilibrium condition, process output continuously fluctuates over a considerable period of time. In practice a number of industrial processes like combustion chamber, distillation column, chemical reactors are well-known integrating processes with considerable time delay. Smith predictor based control technique is an established methodology for controlling such processes with considerable dead time. But, this technique fails to perform satisfactorily for pure integrating processes with considerable time delay. Modified Smith predictor method by Majhi and Atherton may be considered to be a good alternative. However, its performance is not found to be quite satisfactory due to undesired overshoot and sluggish recovery. In addition, complexity lies with the tuning of three controllers involved in multi-loop structure. To overcome this limitation, a simple tuning methodology is proposed here for modified Smith predictor with two controllers only. Efficacy of the proposed mechanism is substantiated through performance evaluation of pure integrating processes with significant time delay in comparison with well-known modified Smith predictor tuning reported by Majhi and Atherton. © 2019 IEEE.

Proceedings of 3rd International Conference on 2019 Devices for Integrated Circuit, DevIC 2019

Set point weighted modified Smith predictor for delay dominated integrating processes

Responses of high-order systems under ZieglerNichols tuned PI controllers (ZNPIs) are characterized by excessive oscillation with a large overshoot. Although, a fixed set-point weighting based PI controller (FSWPI) may decrease the overshoot considerably, it fails to reduce the oscillation in the set-point response. Moreover, both FSWPI and ZNPI exhibit equally poor load regulation. Keeping in mind an overall improved performance, we propose an online dynamic set-point weighting technique for ZNPIs. The dynamic set-point weighting factor (βd) is heuristically derived from the instantaneous process trend. Performance of the proposed dynamic set-point weighting based PI controller (DSWPI) for various second- and third-order processes including a pH process shows a significant improvement during both the set-point and load disturbance responses over other methods. Stability and robustness of the proposed DSWPI are addressed. Effectiveness of the DSWPI is demonstrated through the real-time implementation on a practical DC position control system. © 2011 ISA. Published by Elsevier Ltd. All rights reserved.

Performance improvement of PI controllers through dynamic set-point weighting

A simple method is proposed for PI, PD and PID controller settings for an integrating plus dead-time transfer function model. The method is based on matching the coefficients of corresponding powers of s in the numerator and that in the denominator of the closed-loop transfer function for a servo problem. The derived controller transfer function is found to be a PD controller which is recently also shown by Visioli [IEE Proc. Control Theory Appl. 148 (2001) 180] by minimizing the integral squared error (ISE) using a genetic algorithm. It is shown that the PD controller gives offset for regulatory problems. A method is proposed for designing PI and PID controllers. The performance of the PID controller is shown to be better than that proposed by Visioli. A set-point weighting parameter is used to reduce the overshoot for the servo problem. © 2002 Elsevier Science Ltd. All rights reserved.

Computers and Chemical Engineering

A simple method of tuning PID controllers for integrator/dead-time processes

A systematic method is given for selection of the set point weighting parameter (b) in the PI/PID controller for stable first order plus time delay systems. The parameter b is selected to minimize the over shoot for a servo problem. The responses of the PID controllers, designed by Ziegler-Nichols method or by pole placement method, without and with the set point weighting are compared. The present method significantly reduces the overshoot.

Chemical Engineering Communications

Set point weighted PI/PID controllers

Unsolved Problems in Mathematical Systems and Control Theory

Problem 8.3 Determining the least upper bound on the achievable delay margin

Journal of Process Control

A double two-degree-of-freedom control scheme for improved control of unstable delay processes

IEE Proceedings - Control Theory and Applications

New modified Smith predictor scheme for integrating and unstable processes with time delay

Set point weighted modified Smith predictor for integrating and double integrating processes with time delay

Journal	ISA Transactions
Publisher	ISA - Instrumentation, Systems, and Automation Society
ISSN	00190578
Open Access	No