Design of Fractional Filter Fractional Order Proportional Integral Derivative (FFFOPID) controller for higher order systems

This article presents a Fractional Filter Fractional Order Proportional Integral Derivative (FFFOPID) controller design method for higher order systems, approximated as Non-Integer Order Plus Time Delay (NIOPTD) models. The design uses an Internal Model Control (IMC) scheme and the resulting controller has a series form of Fractional Order Proportional Integral Derivative (FOPID) term, in series with a fractional filter. An analytical tuning method is then used to identify the optimum controller settings. Simulation results on different systems show that the proposed method gives better output performance for set point tracking, disturbance rejection, parameter variations, and for measurement noise in the output. The robust stability of the system regarding process parametric uncertainties is verified with robustness analysis. Controllability index analysis is also undertaken to ascertain the closed loop system performance and robustness.