A.H Ahmadi - Department of Electrical Engineering Amirkabir University of Technology (Tehran Polytechnic) Tehran, Iran
T.V Moghaddam - Department of Electrical Engineering Amirkabir University of Technology (Tehran Polytechnic) Tehran, Iran
S.K.Y Nikravesh - Department of Electrical Engineering Amirkabir University of Technology (Tehran Polytechnic) Tehran, Iran

In recent years, fractional order systems have attracted more and more attention in various fields. However, the control design techniques available for the fractional order systems suffer from the lack of direct systematic approaches. The objective of this work is to find out optimum settings for a fractional order derivative integral (FO-DI) controller in order to fulfill three different robustness specifications of design for the compensated system. The tuned FO-DI controller can ensure that the given gain crossover frequency and phase margin are fulfilled and then the phase Bode plot is flat at the given gain crossover frequency. Consequently, the closed-loop system is robust to gain variations. The fractional order controller design method proposed in this paper is practical and simple to apply. The simulations results show that the closed-loop system can achieve favorable dynamic performance.

Fractional order system, Fractional calculus, Controller tuning, Frequency domain specifications, Robustness