Analytical design of fractional IMC filter – PID control strategy for performance enhancement of cascade control systems

Abstract

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.

KEYWORDS:

• Cascade loop
• fractional IMC filter
• robustness
• fragility

Disclosure statement

No potential conflict of interest was reported by the author(s).

ORCID

Rayalla Ranganayakulu http://orcid.org/0000-0002-5383-9067

Ambati Seshagiri Rao http://orcid.org/0000-0002-2575-9318

Gara Uday Bhaskar Babu http://orcid.org/0000-0002-1208-5238

Additional information

Notes on contributors

Rayalla Ranganayakulu

Rayalla Ranganayakulu is a Ph.D. candidate in the Chemical Engineering Department of National Institute of Technology Warangal, India. His research interests are process control, fractional order control and advance control of time delay systems.

Ambati Seshagiri Rao

Ambati Seshagiri Rao has been working as an associate professor in the Department of Chemical Engineering, National Institute of Technology Warangal, India. He received his PhD degree from IIT Madras in Chemical Engineering. His research interests include process dynamics and control, pid tuning, time delay systems and waste water treatment.

Gara Uday Bhaskar Babu

Gara Uday Bhaskar Babu has been working as an assistant professor in the Department of Chemical Engineering, National Institute of Technology Warangal, India. He received his PhD degree from IIT Kharagpur in Chemical Engineering. His research interests include fractional order PID, model-based control, modelling and simulation, nonlinear control and process intensification.