## 1 Introduction  
Load frequency control (LFC) is a fundamental part of large scale power system operation and control. Due to the importance of the distribution of electrical power, the power companies are responsible for providing uninterrupted, reliable, efficient and effective power supply to their customers with satisfactory power quality. A modern electrical network is made up of diverse controlled areas and for stable operation of the utilities, the total generation of each control area must equal the total load demand plus associated plant losses [1; 2]. LFC is continuously observing the system frequency and tie-line power and appraising the net changes of the same from their prescribed values (known as area control error (ACE)) [3]. Then adjust the valve settings of generators accordingly, so as to maintain ACE at its minimum value. The main objective of LFC is to regulate power produced from various utilities in each area such that the frequency and tie-line power are kept within stated limits [2; 4]. The diverse generation units in power plants are coherently interconnected by a stiff network, which is why the frequency deviations are supposed to be equal in an area. An adequate controller designed for the power plant must cope with load demand and system perturbations, and it should provide an acceptable level of the power output, while keeping the frequency within stated limits [5]. With the growth in size and complexity of modern power plants, insufficient control might deteriorate the frequency and plant oscillation may spread into a wide area resulting in system blackout. Thus, the designed controller for such power systems must overcome these limitations. So far, several control strategies like a fuzzy logic controller, optimal control, adaptive control, self-tuning control, robust, intelligent control and storage devices, and so forth, have been proposed for the power plant to ameliorate the dynamic performances under load perturbations (LPs) and parameter variations [2; 4; 6; 7; 8; 9; 10; 11; 12]. A Feedback controller strategy based on battery storage is proposed for the frequency stabilization of the island wind power plant to predict the power balance variations [8]. A battery energy storage system (BESS) is proposed for the power plant to perform frequency stabilization in a grid-connected wind park, as well as to explore the performance and drawbacks through the implementation of the controller strategy [9]. It is worth noting that the application of the fuzzy logic controllers (FLCs) system, in the control theory, have concerned handling intricate and nonlinear systems. The FLCs have been endorsed over the traditional controllers due to their several merits such as the incorporation of human expert knowledge, the fact that no accurate dynamic model is required and that they require fewer maintenance costs and so forth. Unlike the conventional PID controllers, FLCs can achieve effective for the control of nonlinear and uncertain plants. As a result, several researchers have proposed the different design architectures of FLCs and applied to several systems among which some of them are considered in the following. A novel hybrid FLC based intelligent proportional-integral-derivative (PID) (FLiPID) controller is proposed for load frequency stabilization of interconnected large-scale power plant with the consideration of nonlinearities [4]. In Reference [10], the authors designed a controller based on a fuzzy PID controller to solve the LFC problem for interconnected power plants, where the controller gains are tuned via the Firefly algorithm (FA). A novel hybrid Firefly Algorithm and Pattern Search (hFA-PS) technique is proposed for the load frequency control (LFC) of interconnected large-scale power systems with the consideration of the generation rate constraint (GRC) [11]. The fuzzy pre-compensated PID (FP-PID) controller is proposed for a DC servomotor, having unidentified uncertainties with varying in load perturbations [12].