581 Application of Classical and Fuzzy Logic Controllers for AGC under Deregulated Environment K. Chandra Sekhar * , K. Vaisakh * * Department of electrical engineering AU College of Engineering, Andhra University, Visakhapatnam-530003, AP, India {kona.chandrasekhar699@gmail.com, vaisakh_k@yahoo.co.in} Abstract—Automatic generation control (AGC) of a power system provides power demand signals for power generators to control frequency and tie-line power flow due to the large load changes or other disturbances. Occurrence of large real power imbalance causes large frequency deviations from its nominal value which may be a threat to secure operation of power system. To avoid such situation, emergency control to maintain the system frequency using classical controllers and fuzzy logic controller is proposed in this paper. The performance of both classical and fuzzy logic controllers is compared under three different cases in deregulated environment. It is observed that the fuzzy logic based controller give better optimal transient response of frequency and tie line power changes compared to classical controllers. Index Terms—Automatic generation control, classical controllers, fuzzy logic controllers, deregulated environment. I. INTRODUCTION Automatic generation control (AGC) plays an important role in the power system by maintaining scheduled tie power and scheduled system frequency in normal operation and during small perturbation. The objective of AGC is to maintain the area generation–demand balance by adjusting the outputs on regulating units in response to deviations of frequency and tie-line exchange. A large number of controllers are used to maintain a power system in a normal state of operation. Simple classical controllers for AGC are still popular with the industry because of their inherent simplicity, easy realization, and low cost and because of the decentralized nature of their control strategy. Several classical controllers such as Proportional(P), Integral (I), Proportional– Integral (PI), Integral–Derivative (ID), and Proportional–Integral– Derivative (PID) have been used in AGC as secondary controllers, but surprisingly there is hardly any literature that compares performances of these controllers on deregulated AGC model to establish the best of this lot. The controller gains are set to a level that compromises between fast transient recovery and low overshoot in the dynamic response of the overall system. Many approaches have been proposed over the past decades regarding the load-frequency control of single and multi area power systems. The main purpose of designing load-frequency controllers is to ensure the stable and reliable operation of power systems. Since the components of a power system are non linear, a linearized model around an operating point is used in the design process of L-F controllers. Some of the proposed methods in literature deal with system stability using fixed local plant models ignoring the changes on some system parameters [1-5]. Recently, fuzzy logic controllers based on fuzzy set theory are used to represent the experience and knowledge of a human operator in terms of linguistic variables that are called fuzzy rules. Since an experienced human operator adjusts the system inputs to get a desired output by just looking at the system output without any knowledge on the system’s dynamics and interior parameter variations, the implementation of linguistic fuzzy rules based on the procedures done by human operators does not also require a mathematical model of the system. Therefore a fuzzy logic controller (FLC) becomes nonlinear and adaptive in nature having a robust performance under parameter variations with the ability to get desired control actions for complex, uncertain, and nonlinear systems without the requirement of their mathematical models and parameter estimation. Fuzzy logic based controllers provide a mathematical foundation for approximate reasoning, which has been proven to be very successful in a variety of applications [3]. In a restructured power system, the engineering aspects of planning and operation have to be reformulated although essential ideas remain the same. With the emergence of the distinct identities of GENCOs, TRANSCOs, DISCOs and the ISO, many of the ancillary services of a vertically integrated utility will have a different role to play and hence have to be modelled differently. Among these ancillary services is the automatic generation control (AGC). In the new scenario, a DISCO can contract individually with a GENCO for power and these transactions are done under the supervision of the ISO or the RTO. In this paper, the two area dynamic model formulated following the ideas presented by Kumar et al. [6], [7] is considered for application of different classical controllers and fuzzy logic controllers. The concept of a DISCO participation matrix (DPM) which helps the visualization and implementation of the contracts is also considered. The traditional AGC is well discussed in the papers of Elgerd and Fosha [8], [9]. Research work in deregulated AGC is contained in [6], [7], [10], [11]. II. RESTRUCTURED POWER SYSTEM In the restructured or deregulated environment, vertically integrated utilities no longer exist. The utilities no longer own generation, transmission, and distribution; instead, there are