Digital Realization of Retuning Fractional-Order Controllers for an Existing Closed-Loop Control System

In the present paper, the problem of digital implementation of retuning fractional-order (FO) controllers for an unstable plant-a real-life laboratory model of a Magnetic Levitation System (MLS) - is investigated. Retuning control is applied to an existing closed-loop PID control system through the use of a hardware FO controller prototype. An implementation method for the retuning controller is proposed. Three types of hardware-in-the-loop (HIL) experiments are considered. First, the plant is simulated using a suitable dynamic model. Second, the real-life laboratory model of the MLS is controlled. In the third type of experiment, a MATLAB implementation of the retuning controller is evaluated as a benchmark. Three controllers obtained in an earlier work are tested with this setup. Experimental results are compared and discussed.