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Top1. Introduction
The interconnected power system generation is made up of several areas. In each area, load frequency controller (LFC) monitors the system frequency and tie line flows, computes the net change in the generation required and changes the set positions of the generators within the area to keep the time average of the area control error (ACE) at a low value. The aim of LFC is to achieve zero static frequency error, distribute generation among areas so that interconnected tie line flows match a prescribed schedule and balance the total generation against the total load and tie line power exchanges. The overall aim of power system engineer is to provide a good quality of electricity to the consumer. For this reason a power system must be maintained at the desired operating level characterized by constant frequency, voltage profile and load flow configuration. As the demand deviates from its nominal value with an unpredictable small amount, the operating point of power system changes, and hence, system may experience deviations in nominal system frequency and scheduled power exchanges (Kothari & Nagrath, 2011; Kothari & Dhillon, 2010; Majhi, 2009; Ibraheem & Kothari, 2005; Elgerd & Fosha, 1970).
All conventional LFC schemes have two substantial problems (1) increasing the gain of frequency feed-back will result in LFC loop instability, i.e., frequency drop control range will be limited (2) they will be unstable if there is any load disturbance in the power system. Substitution of the conventional proportional integral (PI) controller with a new PID controller can improve the operation of LFC. In conventional studies, frequency oscillations of the system are minimized by using conventional linear controllers (Tripathy, Hope & Malik, 1982). In general, different conventional control strategies are being used for LFC. Yet, the limitations of conventional PI and PID controllers are: slow and lack of efficiency and poor handling of system nonlinearities.
The researchers in the world over trying to employ several strategies for LFC of power systems to maintain the system frequency and tie line flow at their scheduled values during normal operation and also during disturbance conditions. A critical literature review on the LFC of power systems was presented in (Saikia, Nanda & Mishra 2011) where different control techniques pertaining to LFC problem were discussed.