A Comparative Study Between Cascaded FOPI–FOPD and IOPI–IOPD Controllers Applied to a Level Control Problem in a Coupled Tank System

Abstract

This paper presents a novel liquid level control of a coupled two tank SISO system. Physical system is modeled from the open loop experimental response in two stages. A cascade control strategy is adopted. Fractional Order Proportional Integral (FOPI) and Fractional Order Proportional Derivative (FOPD) controllers are designed for the outer and inner loop, respectively, using frequency domain method. Similarly, conventional Integer Order Proportional Integral and Integer Order Proportional Derivative controllers are also designed to compare the performances. Reference signal tracking performance is tested with multiple step, ramp and sinusoidal reference signals. Ability of disturbance rejection is tested by adding more water into the tanks through a disturbance input channel. Experimental results reveal that the proposed FOPI–FOPD control scheme outperforms its integer order counterparts both in terms of reference signal tracking and disturbance rejection.