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

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.

Note that even for the same type of set-point and load disturbance, the water-bed effect between the set-point response and the load disturbance response will become very severe for an integrating or unstable process in the unity feedback control structure (Zhou et~al. 1996).

A two-degree-of-freedom control scheme is proposed for enhanced control performance of integrating and unstable processes with time delay. The two controllers in the scheme are well placed to tune from the setpoint and disturbance. The design steps of these two controllers are independent. The H 2 optimal control method is used to design the set-point tracking controller and an optimal internal model control (IMC) filter structure is proposed to design a proportional-integral-derivative (PID) controller that produces an improved disturbance rejection response. The setpoint and load disturbance responses can each be tuned conveniently by a single control parameter. Especially, improvement of disturbance response is extremely great compared with recently reported methods. Illustrative examples show the simplicity and superiority of the proposed controller design method over previously published approaches both for the setpoint response and for the load disturbance rejection.

A two-degree-of-freedom control scheme is proposed for enhanced control performance of unstable processes with time delay. The two controllers in the scheme are well placed to tune from the setpoint and disturbance. The design steps of these two controllers are independent. The H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> optimal control method is used to design the set-point tracking controller and an optimal internal model control (IMC) filter structure is proposed to design a proportional-integral-derivative (PID) controller that produces an improved disturbance rejection response. The setpoint and load disturbance responses can each be tuned conveniently by a single control parameter. Especially, improvement of disturbance response is extremely great compared with recently reported methods. Illustrative examples show the simplicity and superiority of the proposed controller design method over previously published approaches both for the setpoint response and for the load disturbance rejection.

Location of poles on the right hand side of s-plane for a process provides unstable behaviour. Obtaining desired output from an unstable process is truly a difficult task especially for processes with considerable dead time. Processes like combustion chamber, distillation column, and chemical reactors are well-known unstable processes with considerable time delay. Smith predictor based control technique is a well-known methodology for controlling such processes with considerable dead time. But, this technique fails to perform satisfactorily during transient as well as steady state operating phases for delay dominated unstable processes. To ensure improved close-loop response for delay dominated processes, Majhi and Atherton proposed modified Smith predictor technique. However, its performance is not found to be adequate, in addition tuning of more than one controller is quite complicated for delay dominated processes with pole located on right half plane. To overcome this limitation, here we propose a unified tuning methodology with simple modified Smith predictor scheme which is capable to provide an overall improved performance in terms of enhanced load recovery. Effectiveness of the proposed scheme is verified through simulation study with the well-known delay dominated unstable process models representing the behavior of chemical reactor and distillation column in comparison with conventional and modified Smith predictor methodologies.

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.

DOMINANT POLE DESIGN - A UNIFIED VIEW OF PID CONTROLLER TUNING

This study presents the development of dead-time compensator with Proportional Integral-Derivative (PID) controller and their implementation in real-time using the Programmable Logic Controller (PLC) on a heater-furnace system that constitute the temperature process. Though PID controller is effective to most of the processes, it has draw backs when used to control the processes with significant dead time. Therefore to eliminate the effects of long dead time, the dead-time compensator combined with PID is proposed. The control equation for the proposed dead time compensator is developed using the mathematical model of heater-furnace system and ladder logic program is created in GE Fanuc Versamax PLC. The PID controller is tuned using process reaction curve method and programmed in PLC. The proposed controller has an outer loop control mechanism with dead time compensator which feeds the inner loop PID controller. The effects of dead time on the performance of PID controller are eliminated through the outer loop control mechanism whose output does not contain modelling errors. The results of the proposed dead-time compensator with PID are compared with the results of the conventional PID controller without dead time compensation for both steady state response and servo-regulatory response. The results of the proposed controller show better improvement in the time domain specifications compared to conventional PID controller.

The compensation of process with time delays has been of interest to academics and pratitioners for several decades. Additionally, proportional integral derivative (PID) controllers are widely used in the process industries. The simplicity and the ability of these controllers to solve most practical control problems have greatly contributed to this wide acceptance. However, they may not provide satisfactory closed loop responses when the process considered is either a high-order plant or a plant with a long dead time. In these cases a powerful technique, the Smith predictor, can be used. However, these regulators cannot reject load disturbance for processes with integration. A review of the literature for compensation methods of process with time delay and Smith predictor (and its modifications) is presented. The focus of the thesis is subsenquently broadened with the consideration of compensation methods for integrating process and the proposition of a new approach. The proposed method for PID (or its variations) controllers is based on the specification of the desired closed loop transfer function for disturbances. Although the approach is designed for disturbance rejection, the set-point responses are usually satisfactory and can be independently tuned. Simulation examples show the simplicity and better robustness of the proposed method over previously published approaches both for the set-point response and for the load disturbance rejection.

The autotuned dead-time compensating control system with improved disturbance rejection

In this paper, we shall present simple and effective tuning&#13;\nformulas for IMC controllers when they are applied&#13;\nto second-order plus dead-time processes (SOPDT). We&#13;\nhave discovered that for controllers designed by applying&#13;\nIMC method, the proportional gain, the integml gain,&#13;\nthe derivative gain of the PID part of the controller&#13;\nand un associate filter should all be modified according&#13;\nto the given.formulas for the purpose of achieving&#13;\nset-point response and disturbance rejection tradeoff.&#13;\nThe study has also shown that the tradeoff between setpoint&#13;\nresponse and disturbance rejection is limited by&#13;\nnormalised dead time of the SOPDT processes for the&#13;\nsimple pole cases.

This paper studies anti-windup control design for process with dead time and integrator. Based on the two degrees of freedom (2DOF) control schemes presented by Yu-Chu Tian, et al, the effects of actuator saturation are studied. An anti-windup scheme for the modified Smith predictor is proposed. Some problems in stability analysis are presented. Computer simulations show the significant performance improvement when the set point or disturbance is large enough.

For an inverter drive induction motor control system, a typical problem encountered is the nonlinear voltage gain caused by the non ideal characteristics of the power inverter. The switch dead time will introduce waveform distortion and fundamental voltage drop to the system. If not compensated, such distortions will introduce harmonic components which will cause additional loss in the induction machine. Therefore, the impact of harmonics caused by switching dead time are essential to induction motor drive design, especially when the motor is running at low speed. In this paper, a dead time compensation method is proposed. By adding a 6th order resonant controller to the existing current loop PI controller, the negative sequence 5th order and positive sequence 7th order current harmonics caused by the dead time are eliminated. The overall control scheme is implemented in synchronous rotating d-q reference frame. The controller resonant frequency is 6 times to the synchronous frequency, which is calculated with mechanical speed and slip. Experiment results of steady state and dynamic response studies are presented to validate the effectiveness of the proposed method.

Dead time compensation circuit for radiation detector

Anti-Jerk Control of a Parallel Hybrid Electrified Vehicle with Dead Time