Fractional order PID controller for perturbed load frequency control using Kharitonov’s theorem

• Paper suggests fractional order PID controller design for interval plants.
• Proposed method is based on the Kharitonov’s theorem.
• In proposed method stability boundary locus concept is used.
• Proposed controller is more robust than the existing controllers.

In the fast developing world of today, there is an inevident demand of good quality power supply. For this, it is very essential that the present day power systems should possess efficient control algorithms for the load frequency control. Although, in recent years, lot of research has been carried out in this direction however, the parametric uncertainty and rejection of the external disturbances continue to remain important issues for the LFC design engineers. The control algorithms based on fractional order control are known to possess excellent disturbance rejection capability as well as high robustness towards the system parameter variations. Further, a higher level of robustness can be incorporated in the system by using an interval model of the plant while designing the controller. Therefore, in this paper a fractional order PID controller is designed for the interval model of the single area load frequency control using the Kharitonov’s theorem. This technique gives freedom to the design engineer to decide the limits of the parameter variations up to which the controller is required to perform well. This helps in improving the system performance as well as the overall safety of the system by preventing the system breakdown that may occur due to sudden increase in any system parameter. Finally, the performance of the proposed controller is compared to the nominal controllers existing in the literature and evaluated on the basis of the various integral error criterion. It is observed that the proposed controller gives the best performance and is capable of stabilizing the system for a larger range of system parameter variations.