Modified Smith predictor based optimal fractional PD-PD controllers for integrating first order plus time delay processes

A modified Smith predictor structure is framed with a pair of fractional order proportional derivative (FOPD) controllers to ascertain enhanced closed loop responses for integrating first order plus time delay processes. The proposed design involves two FOPD controllers, one is in the forward path and the other is in the feedback path along with a low pass filter (LPF). Both the controllers are accountable for improved servo and regulatory responses and the LPF works towards noise elimination. Rao-2 optimization algorithm is employed to find out the design parameters of fractional controllers and the associated LPF is designed based on the value of closed loop time constant of the concerned process. Closed loop performance is evaluated for FOPD controller optimized with Rao-2 approach as well as other three well-known nature inspired algorithms. Relative performance analysis of the proposed controller is made in comparison with recently reported works on integrating first order plus time delay (IFOPTD) models. Robust stability and uncertainty handling capability of the proposed control structure are also investigated using small gain theorem under process gain and dead-time perturbations. The proposed scheme is found to exhibit considerable robustness against model uncertainties and external disturbances.