Robust Fractional Order Flow Control in an Oil Pipeline

Abstract

The robust fractional order oil flow control in an oil pipeline is addressed in this paper. An experimental identification based on a step like input was developed which yielded a second order transfer function with a zero and a time varying time delay. Controllers are subsequently designed with nominal phase margin and zero steady state error of the closed-loop step response specifications, plus robust damping expressed in terms of a maximum allowed variation of the phase margin of ±10% around the nominal value. We have considered integer and fractional order controllers. Rules to tune the parameters of these controllers have been obtained and a condition to get minimum phase closed-loop systems has been derived. We have shown that PI controllers verifying the three design conditions often yield undesired nonminimum phase closed-loop systems. This is avoided using the proposed fractional order controllers. Simulations carried out in this paper illustrate these results.