ROBUSTNESS EVALUATION OF A MULTIVARIABLE FRACTIONAL ORDER PI CONTROLLER FOR TIME DELAY PROCESSES

Fractional order calculus is currently experiencing a wide application in controlling different types of processes. The focus has been directed towards the design of robust controllers for single-inputsingle-output systems, with very few tuning examples for the multivariable ones. The purpose of the present paper is to describe a simple and effective method for designing a multivariable fractional order PI controller for a multivariable time delay system. The main idea of the tuning procedure is extended from the singleinput-single-output case with the simple use of a steady state decoupling technique. The design method is based on performance specifications that ensure a certain settling time and on a gain robustness condition. The solution is found by using an iterative procedure. The case study presented demonstrates the efficiency of the proposed control design, the closed loop system behaving robustly to significant gain variations ranging +/- 30%. Also, the robustness of the fractional order multivariable controller is tested against time delay variations.