Quantitative Performance Design of a Modified Smith Predictor for Unstable Processes with Time Delay

Abstract

The existence of both right-half-plane poles and time delay makes it difficult to obtain a higher control quality. Recently, a modified Smith predictor for unstable processes with time delay was presented and good performance was obtained. In this paper, the modified Smith predictor is discussed. A modified structure is presented. The new one not only is simple for analysis and design but also avoids the improper element. Instead of introduction of an inner loop, a direct design procedure is given and analytical formulas for the controllers are provided. The time domain performance for both trajectory and regulatory responses is obtained quantitatively. Sufficient and necessary conditions for robust stability are also given. The new structure and design method can also be used for the control of integrating processes with time delay and stable processes with time delay. Numerical examples are provided to illustrate the proposed method.

A unified approach for proportional-integral-derivative controller design for time delay processes

“…In the case of derivative filter for ideal form of PID controller in Eq. (20), any recommended filter parameter is not safe, rather than that the design of the derivative filter should be an integral part of PID control. Based upon the profound analysis with examples presented by Visioli [43], it can be concluded that, for a PID controller in series form, it is reasonable to choose a fixed derivative factor N>10.…”

“…For this reason, some modified IMC methods of two-degreesof-freedom (2DOF) control were developed for controlling unstable processes with time delay, such as those proposed by Lee et al [12], Yang et al [13], Wang and Cai [14], Tan et al [15], Liu et al [16] and Jung et al [17]. In addition, 2DOF control methods based on the Smith-Predictor (SP) were proposed by Majhi and Atherton [18], Kwak et al [19], and Zhange et al [20] to achieve a smooth nominal setpoint response without overshoot for first-order unstable processes with time delay.…”

Predictor-Based Disturbance Rejection Control for Sampled Systems With Input Delay

“…In fact, the classical SP or the similar internal model control (IMC) scheme can only be used for stable processes with time delay due to the internal stability issue [13]. Modified SP or IMC designs have been proposed in the literature (e.g., [4,5,[14][15][16][17][18]) for application to integrating and unstable processes with time delay. It was demonstrated that the filtered SP (FSP) [4,5], which gives a delay-free output prediction, could be generally used for open-loop stable, integrating and unstable processes with time delay.…”

Design of advanced PID controller for enhanced disturbance rejection of second‐order processes with time delay

“…Therefore, some modified IMC methods [10][11][12][13][14] of two-degree-of-freedom (2DOF) control were developed for controlling unstable processes with time delay. Several tuning methods [15][16][17] have been proposed based on the Smith-Predictor (SP) to achieve a smooth nominal set-point response without overshoot for first-order unstable processes with time delay. Both the modified IMC and the modified SP methods have the advantage of a faster nominal set-point response without overshoot for unstable processes.…”