Design of FOPI Controller for Time Delay Systems and Its Experimental Validation

In this paper, we report on the identification and modeling of unknown and higher order processes into first order plus dead time (FOPDT) plants based on the limit cycle information obtained from a single relay feedback test with an online fractional order proportional integral (FOPI) controller. The parameters of the test processes are accurately determined by the state space method while the FOPI controller settings are re-tuned to achieve enhanced performance based on the identified model parameters based on the balanced-tuning method. A new performance index, integral time fractional order absolute error (ITF_IAE) is introduced in this paper for balanced tuning of fractional order (FO) controllers. It requires minimum design specifications without a-priori knowledge of gain and phase crossover frequencies and is done non-iteratively without disrupting the closed loop. Four test processes and experimental analysis on a coupled tank system (CTS) validate the theory proposed.