Robust Fractional Order Flow Control in an Oil Pipeline

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.