Fractional order PID controller design for an FOPDT model by online tuning method

In this paper, an online tuning of fractional order proportional integral and derivative controller is proposed. Here, the process parameters of an unknown plant is first modeled into an equivalent First Order Plus Dead Time(FOPDT) process by using online method where an ideal relay is connected in parallel to a Fractional Order Proportional Integral Derivative (FOPID) controller. The FOPID controller is re-tuned after obtaining the equivalent model. The advantage of this online tuning method is that it ensures that the controller always stays in loop. This method is then verified through the simulations of certain process models.