A fractional order PID-based sliding mode controller approach for chemical processes

Abstract

This paper proposes a novel control strategy for chemical processes by integrating fractional-order PID (FOPID) controllers with sliding mode control (SMC). Through the use of the enhanced flexibility and superior tuning capabilities of FOPID controllers over traditional PID schemes, the method replaces the classical discontinuous switching mechanism of SMC with a smooth fractional-order control action. The proposed hybrid approach is evaluated through simulations in two nonlinear systems, a mixing tank with variable time delay and a pH neutralization process, and experimentally validated using the TCLab device. Throughout three case studies, the method demonstrates improvements in performance and response between 40% and 10% compared to the other two SMC alternatives. Furthermore, the approach effectively reduces chattering, improves convergence speed, and improves robustness to measurement noise, contributing to extended actuator lifespan. This makes the proposed methodology particularly attractive for chemical process applications, offering a practical and accessible solution for plant operators by enabling the utilization of robust control techniques without requiring deep expertise in nonlinear control design.