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


Abstract: The coupled tank system (comprising two tanks) is used in the chemical industries, water treatment plantsetc. Level control of the coupled tank system is a common problem in the process control industry. This work proposes afractional order internal model controller (FOIMC) with a higher order fractional filter for the level control of the coupledtank system. A first order plus delay time (FOPDT) model of the system is used in the controller design. FOIMC hasadvantages like robustness to changes in the system gain and extended stability margins. The proposed higher orderfractional filter makes the controller physically realizable and quickly roll off the magnitude Bode plot, neglecting thehigh frequency noise. The particle swarm optimisation (PSO) algorithm is a swarm intelligence based algorithm usedfor the optimisation problems. The parameters of the FOIMC are optimized with the PSO algorithm by minimizingan objective function constructed using time domain specifications. The novel objective function includes weightedpeak 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 ofthe 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 theexperimental results are compared.

Keywords: Fractional order internal model controller, particle swarm optimisation algorithm, higher order fractionalfilter, coupled tank system

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