The cascade control is widely used in chemical industries for disturbance attenuation as an alternative to a single feedback loop. This article presents an internal model control (IMC)-based series cascade control system for different time delay process models. The novelty of the work lies in the use of fractional order IMC filter of the first order and higher order for designing controller in the outer loop based on specific maximum sensitivity. The design also considers different approximations for the time delay term. The controller designed for the inner loop assumes the standard PID controller structure and the outer loop controller takes a fractional filter PID structure. The proposed method gives improved performance for set point tracking and disturbance rejection. Further, the proposed method gives robust performance for noise in the measured signal. Also, the robustness analysis is performed to know the insensitivity of the closed-loop system for process parameter variations. The fragility of the controller is investigated for perturbations in the controller parameters.

中文翻译：

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分数阶 IMC 滤波器的解析设计——用于级联控制系统性能增强的 PID 控制策略

串级控制广泛应用于化工行业，用于衰减干扰，作为单反馈回路的替代方案。本文介绍了一种基于内模控制 (IMC) 的串联串级控制系统，适用于不同的延时过程模型。这项工作的新颖之处在于使用一阶和更高阶的分数阶 IMC 滤波器来设计基于特定最大灵敏度的外环控制器。该设计还考虑了时间延迟项的不同近似值。为内环设计的控制器采用标准PID控制器结构，外环控制器采用分数滤波器PID结构。所提出的方法为设定点跟踪和干扰抑制提供了改进的性能。更多，所提出的方法为测量信号中的噪声提供了稳健的性能。此外，执行稳健性分析以了解闭环系统对过程参数变化的不敏感性。针对控制器参数的扰动研究了控制器的脆弱性。