Design of Fractional Order PI controller for liquid level control of spherical tank modeled as Fractional Order System

In this paper, Fractional Order Proportional Integral (FOPI) controller is designed for a liquid level control in a spherical tank which is modeled as a Fractional Order System (FOS). The performance of FOPI controller is compared with the traditional Integer Order PID (IOPID) controller designed for the same spherical tank which is modeled as a First Order Plus Dead Time (FOPDT) system in simulation and with the Integer Order PI (IOPI) controller in experimental setup. The FOPI controller is designed following a set of imposed tuning constraints, which can guarantee the desired control performance and the robustness to the loop gain variations. This design scheme offers a practical and systematic way of the controllers design for the considered class of fractional order plant. The integer order controller is tuned based on Ziegler-Nichols (ZN) tuning method. From the simulation and experimental results presented, it is observed that the designed fractional order controller works efficiently, with improved performance comparing with the integer order controller.