Design of the fractional order internal model controller using the swarm intelligence techniques for the coupled tank system

Abstract

The coupled tank system (comprising two tanks) is used in the chemical industries, water treatment plants etc. Level control of the coupled tank system is a common problem in the process control industry. This work proposes a fractional order internal model controller (FOIMC) with a higher order fractional filter for the level control of the coupled tank system. A first order plus delay time (FOPDT) model of the system is used in the controller design. FOIMC has advantages like robustness to changes in the system gain and extended stability margins. The proposed higher order fractional filter makes the controller physically realizable and quickly roll off the magnitude Bode plot, neglecting the high frequency noise. The particle swarm optimisation (PSO) algorithm is a swarm intelligence based algorithm used for the optimisation problems. The parameters of the FOIMC are optimized with the PSO algorithm by minimizing an objective function constructed using time domain specifications. The novel objective function includes weighted peak overshoot, settling time, and integral square error. A MATLAB (MathWorks, Inc., Natick, MA, USA) based tool, fractional order modelling and control (FOMCON) is used to simulate the fractional order controller. Performance of the proposed FOIMC is compared with two state of the art. Robustness to change in the operating point (tank height) is verified. The proposed FOIMC and the state of the art controllers are implemented on the laboratory setup, and the experimental results are compared.