CHAPTER-2 REVIEW OF LITERATURE

Transcription

1 CHAPTER-2 REVIEW OF LITERATURE In this chapter literature survey of different researcher has been carried out. The review of literature is arranged first concept of area wise and the control methodology used like conventional control and intelligent control (fuzzy, ANN and ANFIS). In each section and subsection, literature is arranged as per the year of publication. 2.1 SINGLE AREAS POWER SYSTEM Based on Conventional Control theory Pan C. T. and C. M. Liaw (1989), reported An Adaptive Controller for Power System Load Frequency Control. This paper presents an adaptive controller for load-frequency control of power system. The pole assignment technique is used to find the parameters of the linear controller, and the Popov's theorem is applied to design the parameters of the adaptation mechanism. The simulation results indicate that good control performance can be obtained by this proposed controller, and the performance is insensitive to the plant parameter changes. Wang Y. et al(1994), reported New robust adaptive load-frequency control with system parametric uncertainties. In the paper, based on a combination of the robust control approach and an adaptive control technique, a design procedure of a new robust adaptive controller is proposed for power system load-frequency control with system parametric uncertainties. The simulation results demonstrate that for the example system the proposed load frequency controller can achieve good dynamic performance. Heon-Su Ryu, et al (2000) presented Extended Integral Control for Load Frequency Control with the Consideration of Generation- Rate Constraints. This paper presents an extended integral control to LFC scheme with the presence of Generation Rate Constraints in order to get rid of overshoot of the conventional PI control. The conventional LFC scheme does not yield adequate control performance with consideration of the singularities of speed governor such as rate limit on valve position and GRC. In order to overcome this draw back, an extended integral control is developed for the PI control of the speed governor under the presence of GRC. The key idea of this integral control is using a decoying factor to reduce the effect of error in the past. The simulation results show that the proposed controller based on extended integral control yields much improved control performance, compared to the conventional PI controller. 49

2 Yang Ming-Sheng (2000), presented Load-Frequency Control Scheme for Power Systems Using Smoothed Switching Structure Theory. A design scheme of smoothed switching structure theory based load-frequency control for power systems including parameter uncertainties is presented in this paper. However, knowledge about the bounds of the parameter uncertainties is required for controller design. The basic concept and design scheme of switching structure control are briefly discussed. George Gross and Jeong Woo Lee (2001) presented Analysis of Load Frequency Control Performance Assessment Criteria. This paper presents the development and application of an analytic framework for the formulation and evaluation of control performance criteria in load frequency control (LFC). The framework is constructed so as to explicitly represent the uncertainty in the measured variables in LFC and to use metrics that are meaningful for the structure of the problem. Young-Hyun Moon, et al (2001), presented Power System Load Frequency Control Using Noise-Tolerable PID Feedback. This paper presents a new PID (Proportiona1, Integral and Differential) control scheme based on the feedback of averaged derivatives to realize a noisetolerable differential control with its application to the load frequency control in the power system. It is well known that the LFC (Load Frequency Control) is exposed to the quite noisy environment. The test results show that the proposed controller yields the outputs much closer to the output of the original PID control neglecting noise effects. This demonstrates that the purpose of noise-tolerable control is achieved by the proposed PID control using a delay element. Dulpichet Rerkpreedapong et al (2003) presented Robust Load Frequency Control Using Genetic Algorithms and Linear Matrix Inequalities. In this paper, two robust decentralized control design methodologies for load frequency control (LFC) are proposed. The first one is based on H control design using linear matrix in-equalities (LMI) technique in order to obtain robustness against uncertainties. The second controller has a simpler structure, which is more appealing from an implementation point of view, and it is tuned by a proposed novel robust control design algorithm to achieve the same robust performance as the first one. The simulation results show that the responses of GALMI tuned PI load frequency controllers are almost the same as those of the robust H controllers, which have effective control performance and robustness against possible disturbances Khodabakhshian A. and N. Golbon (2004) presented Unified PID Design for Load Frequency Control. This paper presents a new PID controller for power system load-frequency control. A systematic tuning method is developed. The method is mainly based on a maximum peakresonance specification that is graphically supported by the Nichols chart. The proposed 50

3 controller is simple, effective and can ensure that the overall system performance is desirable. Comparative results of this new load-frequency controller and a conventional PI one show the improvement in system damping remarkably. Giuseppe Dell Olio et al (2005) presented A pluralistic LFC scheme for online resolution of power congestions between market zones. This paper introduces the theoretical aspects and functional design of such an advanced LFC scheme, capable of controlling at the same time the cross border ex-changes of the pluralistic block and the power flows between net-work subareas defined as market zones. Simulations on the Italian power system show the performance, main advantages, and limits of the proposed control method. Guangwei Meng et al (2009) presented power system load-frequency controller design based on discrete variable structure control theory. This paper proposes a discrete-time variable structure reaching law with attenuating quasi-sliding mode band, and gives the variable condition of quasi-sliding mode band. The proposed reaching law is applied to design a load-frequency controller for a power system. The simulation results show that the controller can not only eliminate system chattering, but also improve dynamic performance of the system effectively and make the system possess a strong robustness property. Wen Tan, Zhan Xu (2009), presented Robust analysis and design of load frequency controller for power systems. Robust load frequency control for power systems is discussed. A detailed robustness analysis of the existing control laws shows that parameter variation is not a critical issue but more attention should be paid to the un modeled dynamics in robust load frequency controller design. A new robust load frequency control method is then proposed considering the un-modeled dynamics of power systems. Finally, a new configuration is proposed to overcome the effects of generation rate constraints (GRC). Muwaffaq Irsheid Alomoush (2010) presented Load frequency control and automatic generation control using fractional order controllers. Recently, fractional calculus has received extensive attention and research. Accordingly, there is an increasing interest in fractional-order (FO) dynamic systems and controllers. The widely used classical integer-order proportional integral controller and proportional-integral-derivative controller are usually adopted in the load frequency control (LFC) and automatic generation control (AGC) to improve the dynamic response and to eliminate or reduce steady-state errors. The simulation results show that the proposed FO controllers are robust and competitive to IA-based optimal controllers. Kresimir Vrdoljak et al (2010) presented Applying Optimal Sliding Mode Based Load- Frequency Control in Power Systems with Controllable Hydro Power Plants. In this paper an optimal load-frequency controller for a nonlinear power system is proposed. Due to a non- 51

4 minimum phase behavior of hydro power plants, full-state feedback sliding mode controller must be used. Therefore, an estimation method based on fast output sampling is proposed for estimating the unmeasured system states and disturbances. Finally, the controller parameters are optimized using a genetic algorithm. Simulation results show that the proposed control algorithm with the proposed estimation technique can be used for LFC in a nonlinear power system. Khodabakhshian A. and R. Hooshmand (2010) presented A new PID controller design for automatic generation control of hydro power system. This paper presents a new robust PID controller for automatic generation control (AGC) of hydro turbine power systems. The method is mainly based on a maximum peak resonance specification that is graphically supported by the Nichols chart. The open-loop frequency response curve is tangent to a specified ellipse and this makes the method to be efficient for controlling the overshoot, the stability and the dynamics of the system. Comparative results of this new load frequency controller with a conventional PI one and also with another PID controller design tested on a multi machine power system show the improvement in system damping remarkably. The region of acceptable performance of the new PID controller covers a wide range of operating and system conditions Based on Fuzzy Control Technique Shih Chun Hsu et al (1995) presented Automatic Generation of Fuzzy Control Rules by Machine Learning Methods. This paper presents a multi-strategy learning technique for automatic generation of fuzzy control rules. The resulting decision tree can be easily converted into IF-THEN rules, which are then fuzzified. The fuzzy rules are further improved by tuning the parameters that define their membership functions using the gradient-descent approach. Experimental results of applying the proposed technique to nonlinear system identification have shown improvements over previous work in the area. Chown G.A. and RC. Hartman (1997), presented Design and Experience with a Fuzzy Logic Controller for Automatic Generation Control (AGC). This paper describes the design, implementation and operational performance of a fuzzy controller as part of the Automatic Generation Control (AGC) system in Eskom s National Control Centre. The fuzzy controller was implemented to the control ACE calculation, which determines the shortfall or surplus generation that has to be corrected. The controller was also very simple to implement and configure and could be incorporated as an option on the vendor s product. Ha Q. P. (1998) presented A Fuzzy Sliding Mode Controller for Power System Load-Frequency Control. The application of a robust sliding mode control method to the load frequency control problem of a single area power system is considered in this paper. The control signal consists of 52

5 an equivalent control, a switching control, and a fuzzy control. The influence of not only load changes but also parameter variations and governor S backlash is considered with and without generation-rate constraints. Simulation results demonstrate that the system responses are strongly robust to load disturbances and parameter variations even in the presence of governor s backlash dead band and imposed generation physical constraints. Jawad Talaq and Fadel Al-Basri (1999), presented Adaptive Fuzzy Gain Scheduling for Load Frequency Control. An adaptive fuzzy gain scheduling scheme for conventional PI and optimal load frequency controllers has been proposed. A Sugeno type fuzzy inference system is used in the proposed controller. The Sugeno type fuzzy inference system is extremely well suited to the task of smoothly interpolating linear gains across the input space when a very non-linear system moves around in its operating space. The proposed adaptive controller requires much less training patterns than a neural net based adaptive scheme does and hence avoiding excessive training time. Results of simulation show that the proposed adaptive fuzzy controller offers better performance than fixed gain controllers at different operating conditions. Kazuto Yukita et al (2000) presented Study of Load Frequency Control using Fuzzy Theory by Combined Cycle Power Plant. This paper proposes a new control method using the combined cycle power plant that consists of multi-power generation units, to improve the load frequency control (LFC) characteristics and to secure the regulation capacity in power system. Dulpichet Rerkpreedapong and Ali Feliachi (2002), presented Fuzzy Rule Based Load Frequency Control in Compliance with NERC s Standards. In this paper, a set of fuzzy logic rules is designed to manipulate load frequency controllers of generating units providing regulation and load following services. The fuzzy based load frequency controllers take smart actions that (1) assure compliance with NERC s control performance standards, CPS1 and CPS2, and (2) also reduce wear and tear of generating units equipments. Musiala M. et al (2004), presented An Adaptive Fuzzy Controller Gain Scheduling for Power System Load-Frequency Control. In this paper, an adaptive fuzzy controller gain scheduling scheme for power system load-frequency control is designed to damp the frequency oscillations and to track its error to zero at steady state, A Sugeno type inference system is used in the proposed controller to adapt the scaling gains of a single fuzzy controller through a classical online monitoring of the most sensitive parameters of the system. The proposed controller avoids excessive patterns and training time compared to neural network based adaptive schemes. A typical single-area non reheat power system is considered. Simulation results indicate that the proposed controller is insensitive to parameter changes in a wide range of operating condition, and to the generation rate constraints. Furthermore, it is simple to implement. 53

6 Soundarrajan A. et al (2009), presented Particle Swarm Optimization Based LFC and AVR of Autonomous Power Generating System. In this paper, an evolutionary computing approach for determining the optimal values for the proportional-integral derivative (PID) controller parameters of load frequency control (LFC) and Automatic Voltage Regulator (AVR) system of single area power system using the particle swarm optimization technique is presented.. The results are compared with conventional PID, Fuzzy and GA based controllers Based on ANN Control Technique Murat Luy et al (2008) presented Load Frequency Control in a single area power system by artificial neural network (ANN). In this study, an artificial neural network (ANN) application of load frequency control (LFC) of a single area power system by using a neural network controller is presented. The study has been designed for a single area interconnected power system. The comparison between a conventional Proportional and Integral (PI) controller and the proposed artificial neural networks controller is showed that the proposed controller can generate the best dynamic response for a step load change. The proposed ANN controller is recommended to generate good quality and reliable electric energy Based on Hybrid ANN- Fuzzy Control Technique Vinod Kumar D. M. (1998), presented Intelligent Controllers For Automatic Generation Control. This paper presents a novel approach of Artificial Intelligence (AI) techniques viz., Fuzzy logic, Artificial Neural Network (ANN) and Hybrid Fuzzy Neural Network (HFNN) for the Automatic Generation Control (AGC). The limitations of the conventional controllers Proportional, Integral and Derivative (PID) are slow and lack of efficiency in handling system non-linearities. The intelligent controllers, Fuzzy logic, ANN and Hybrid Fuzzy Neural Network approaches are used for Automatic Generation Control for the single area system and two area interconnected power systems. The performance of the intelligent controllers has been compared with the conventional PI and PID controllers for the single area system as well as two-area interconnected power system. The result shows that Hybrid Fuzzy Neural Network (HFNN) controller has better dynamic response i.e., quick in operation, reduced error magnitude and minimized frequency transients. Mathur H.D. and S. Ghosh (2006), presented A Comprehensive Analysis of Intelligent Controllers for Load Frequency Control. This paper presents summaries of novel approaches of artificial intelligence (AI) techniques, like fuzzy logic, artificial neural network (ANN), hybrid fuzzy neural network (HFNN), genetic algorithm (GA) for the load frequency control of 54

7 electrical power system. The intelligent controllers are used for load frequency control for the single area system. The performance of intelligent controllers with the conventional controllers has been thoroughly compared and analyzed. It is observed that intelligent controllers are found more suitable in present day power system where complexity is gradually increasing day by day. 2.2 TWO AREA INTERCONNECTED POWER SYSTEM Based on Conventional Control Technique Elgerd Olle I. and Charles E. Fosha, (1970), presented Optimum Megawatt-Frequency Control of Multiarea Electric Energy Systems. The North American Power Systems Interconnection Committee recommends that each control area set its frequency bias equal to the so-called area frequency response characteristic (AFRC).The authors question seriously the basis for this practice and prove by the methods of optimum control that better response and wider stability margins can be obtained by lower bias settings. Fosha Charles E. and Olle I. Elgerd (1970), presented The Megawatt-Frequency Control Problem: A New Approach via Optimal Control Theory. This paper records the development of a state variable model of the megawatt-frequency control problem of multi area electric energy systems. The model is in a mathematical form necessary for application of theorems of modem optimal control theory. An optimal feedback controller whose structure is radically different from that considered before is developed. The results of this study allow the authors to suggest feasible ways of greatly improving dynamic response and stability margins of the megawatt-frequency control system. Ashok Kumar, O.P. Malik (1985), presented Variable structure system control applied to AGC of an interconnected power system. A control scheme based on a variable-structure-system concept is applied to the problem of automatic generation control of interconnected power systems. The proposed algorithm is simple and easy to implement. The effect of generation-rateconstraint nonlinearity on the dynamic performance of the system for reheat-and non reheat-type steam turbines is also studied. A comparison of the conventional and the proposed variablestructure control strategies shows that, with the application of the proposed algorithm, the system performance is improved significantly. Song Jiahua and Zheng Xinguang (1985) presented Adaptive control with multistep predictor for power system load frequency. The regulation of electric power is of controlled process with time delay. The time delay is existed because measuring, processing, telecommunication, unit mechanical delay and using simplified model which should have a equivalent time delay to describe a complex system performance exactly. The interest of the paper is put on treating such 55

8 problem. A method of design of adaptive controller for load frequency has been prescribed considering the time-delay. Kothari M.L. & J. Nanda (1988) presented Application of optimal control strategy to automatic generation control of a hydrothermal system. The paper highlights the design of automatic generation controllers through optimal control strategy, for an interconnected hydrothermal system using a new performance index that circumvents the need for a load demand estimator. The dynamic performances of these controllers are analyzed and compared with those obtained through the usual performance index as that used by Fosha and Elgerd (1971), considering a step-load perturbation in either of the areas. Attempt is made to suitably design the new optimal controller that can provide safe generation rate and reasonably good response. Kothari N.L. et al (1989), presented Discrete Mode Automatic Generation Control of Two Areas Reheat Thermal System with New Area Control Error. This paper deals with discrete mode Automatic Generation control of an interconnected reheat thermal system considering a new area control error (ACEN) based on tie-per deviation, frequency deviation, time error and inadvertent interchange. Optimum integral and proportima1 integral controllers using the concept of stability margin and ISE technique have been obtained with conventional ACE and new ACE, and their dynamic performances compared for a step load perturbation. The result reveals that regulator based on the new ACE concept always guarantees zero steady state time error and inadvertent interchange unlike in the case of a controller based on conventional ACE. The settling time for tie-power and frequency deviations is however, somewhat more with the controller based on new ACE. Katsumi Yamashita and Hayao Miyagi (1991) presented Multivariable self tuning regulator for load frequency control system with interaction of voltage on load demand. This paper presents a new method of designing a multivariable self tuning regulator for a load frequency control system with the inclusion of interaction of voltage on load demand. The self tuning controller through speed governor control and excitation control is derived by defining a cost function with a term for presenting the constraints on the control effort, and then by minimizing it with respect to the control vector. The proposed method is applied to a two-area power system provided with non reheat turbines in which the interaction of voltage deviation on load demand is considered, and the control effects of this regulator are examined using digital simulation. Das D. et al (1991) presented Variable structure control strategy to automatic generation control of interconnected reheat thermal system. The paper deals with the analysis of automatic generation control (AGC) of a two-area reheat thermal system considering a variable structure 56

9 controller (VSC) based on the sliding mode concept. Investigation reveals that there is a significant improvement in system dynamic performance with a VSC over that with an integral controller. More over, the variable structure controller is found to be quite insensitive to wide variations of system parameters. A systematic method has been suggested for the designs of variable structure controllers operating in sliding mode for a two equal area reheat thermal system. Khatibi M. H. and O.A. Mohammed (1994) reported An Automatic Two-Area Interconnected System Load-Frequency Control Design. The design, implementation and evaluation of a programmable automatic load-frequency controller for a two- area interconnected system is described. Implementation aspects along with speed requirements of the generators have been fully investigated, taking into consideration the feedback of the output of these generators for comparison with model reference. The described work has been implemented in the power system laboratory at Florida International University. Kourosh Sedghisigarchi et al (2002) presented Decentralized Load Frequency Control in a Deregulated Environment using Disturbance Accommodation Control Theory. In this paper, a decentralized controller is proposed for the load frequency control problem in a deregulated environment. The deregulation scenario considered here assumes that generating units in each area supply regulated power according to their energy contracts. Disturbance Accommodating Controllers (DAC) are designed which are decentralized controllers using frequency and tie-line power measurements only. Hassan Bevrani et al (2003) presented A scenario on Load-Frequency Controller Design in a Deregulated Power System. An approach based on µ synthesis and analysis theory is proposed for the design of load frequency controller in response to the new technical control demand for power system m a deregulated environment. In this approach the power system is considered as a collection of separate control areas and each control area can buy electric power from some generation companies to supply the area-load. The proposed technical scenario is illustrated with application to the design of load-frequency controller for a typical control area the resulting controller is shown to minimize the effect of disturbances and achieve acceptable frequency regulation in presence of uncertainties and load variation. Muthana T. Alrifai and Mohamed Zribi (2005) presented Decentralized Controllers for Power System Load Frequency Control. This paper presents two decentralized control schemes for load frequency control (LFC) of interconnected power systems. The first controller is a state feedback linear controller. The second controller is a nonlinear controller. The two control schemes are designed using Lyapunov theory. For simplicity and without loss of generality, the 57

10 analysis and simulation studies are carried out for a two area interconnected power system. The simulation results indicate that the proposed control schemes work well even in the presence of generation-rate constraints. Moreover, the simulation results show that the proposed controllers are robust to changes in the parameters of the power system. Tyagi Barjeev and S.C. Srivastava (2005) presented A LQG Based Load Frequency Controller in a Competitive Electricity Environment. This paper presents the design of a Linear Quadratic Gaussian (LQG) regulator for the frequency control of a multi-area power system in a restructured competitive electricity market environment. A general model of the LQG regulator has been developed for multi-area system (with hydro and thermal generators) having Poolco and bilateral transactions. Tyagi Barjeev and S. C. Srivastava (2006) presented A Decentralized Automatic Generation Control Scheme for Competitive Electricity Markets. This paper presents the design of a decentralized automatic generation control (AGC) scheme for interconnected multi area power system. The proposed controller incorporates various types of transactions taking place in a competitive electricity market. The controller has been designed by appropriately assigning the Eigen structure of each isolated subsystem via state feedback, satisfying the sufficient conditions for stability. The functioning of the proposed decentralized controller has been demonstrated on a 39-bus New England system and a 75-bus Indian power system, and the results have been compared with those obtained by using a centralized control scheme. Compliance with the North American Electric Reliability Council standards for AGC has also been established. Abolfazl Salami et al (2006) resented The Effect of Load Frequency Controller on Load Pickup during Restoration. This paper proposes a method to improve the frequency response of a power system during restoration. A Load Frequency Control (LFC) scheme with a PID controller is used. In the initial phase of restoration; the proposed control scheme helps to increase the amount of load pick- up. Presented method is capable of achieving better frequency response for a determined load step. The aim is to assess desired frequency response for different power plant. The proposed controller has been tested for different power plants, and simulation results show that the frequency controller can improve load pick-up. Ahmed Bensenouci and A. M. Abdel Ghany (2007) presented Mixed H /H 2 with Pole- Placement Design of Robust LMI-Based Output Feedback Controllers for Multi-Area Load Frequency Control. In this paper, mixed H /H 2 control theory with pole-placement is applied to design centralized and decentralized robust output feedback controllers for Load Frequency Control (LFC) of interconnected power systems. The system performance is analyzed through simulating severe disturbances and wide parameters variation in the presence on the system 58

11 inherent nonlinearity. In both centralized and decentralized cases, the system with the designed robust controllers incorporated is found to fulfill the main LFC requirements. Prasanth B. Venkata and S. V. Jayaram Kumar (2008), presented Load Frequency Control for a Two Area Interconnected Power System Using Robust Genetic Algorithm Controller. In this paper a new robust load frequency controller for two area interconnected power system is presented to quench the deviations in frequency and tie line power due to different load disturbances. The dynamic model of the interconnected power system is developed without the integral control. The area control error is also not included. The frequency and derivatives are zero under normal operation and after the disturbance effects are died. Aswin N. Venkat et al (2008) presented Distributed MPC Strategies with Application to Power System Automatic Generation Control. A distributed model predictive control (MPC) framework, suitable for controlling large-scale networked systems such as power systems, is presented. The overall system is decomposed into subsystems, each with its own MPC controller. These subsystem-based MPCs work iteratively and cooperatively towards satisfying system wide control objectives. Sinha S.K. et al (2008), presented Design of Optimal and Integral Controllers for AGC of Two Area Interconnected Power System. In this work Automatic Generation Control (AGC) of twoarea interconnected power system has been studied. As a consequence of continually load variation the frequency and tie line power deviate over time and these transients are to be minimized using different controllers. An optimal controller has been designed to ascertain zero steady state frequency deviation and tie-line power flow deviation under all operating conditions. For the same two-area system an integral controller has also been designed and the performance of the two types of controllers has been compared. The simulation results indicate that better control performance in terms of overshoot and settling time can be obtained by optimal controller as compared to conventional integral controller. Tyagi Barjeev and S. C. Srivastava (2008), presented Automatic Generation Control Scheme based on Dynamic Participation of Generators in Competitive Electricity Markets. In this paper a general model for multi-area AGC, suitable for deregulated electricity market has been proposed. A dynamic participation factor for Gencos and Discos based on their bid has also been proposed. To develop the model, control areas of different ratings and each area having number of Discos and Gencos with different response rate has been considered. Different types of transactions, possible in the deregulated markets, have also been considered to develop the model. The developed model has been tested on a 75-bus Indian power system, with PID and the fuzzy 59

12 logic based controller. Frequency deviations in all the areas settle down to zero more quickly with the fuzzy logic based controller as compared to the conventional PID controller. Sheikh M.R.I. et al (2009), presented Application of Self-Tuning FPIC to AGC for Load Frequency Control in Multi-Area Power System. In this study, a self-tuning control scheme for SMES is proposed and applied to automatic generation control (AGC) in power system. The system is assumed to be consisting of two areas. The proposed self-tuning control scheme is used to implement the automatic generation control for load frequency control application adding to conventional control configuration. The effects of the self tuning configuration with fuzzy proportional integral controller (FPIC) in AGC on SMES control for the improvement of load frequency control (LFC) is compared with that of PI controlled AGC. Ghazanfar Shahgholian et al (2009), presented Dynamic Analysis and Stability of the Load Frequency Control in Two Area Power System with Steam Turbine. The aim of this paper is to model, analysis and simulation of load frequency control in two area power system and parameters variation effects. State equations of a LFC in two area power system for a steam turbine are proposed. Then by examining some factors such as tie-line stiffness, turbine time constant, inertia constant and damping factor, the frequency control methods and influence of a small load variation are discussed. Finally, the steady state change in frequency in different cases using Matlab is calculate and compared. The response of the system is studied for load each area and parameters changes. Mariano S.J.P.S. et al (2009), presented Optimal Output Control: Load Frequency Control of a Large Power System. This paper addresses the stabilization and performance of the load frequency regulator. The problem is solved by using the theory of the optimal control. An algorithm, based on the new technique, proposed by the authors, to overcome the difficulties of specifying the weighting matrices Q and R, is presented. The algorithm here proposed considers the multi-area electric energy system. The results indicate that the obtained controller exhibits better performance then those based on classic control. Chamnan Koisap and Somyot Kaitwanidvilai (2009) presented A Novel Robust Load Frequency Controller for a Two Area Interconnected Power System using LMI and Compact Genetic Algorithms. This paper proposes a new technique for designing a fixed-structure robust load frequency controller for a two area interconnected power system. The proposed technique uses Linear Matrix Inequality (LMI) method to form an initial solution, and then the global search algorithm, Compact Genetic Algorithm (CGA), is adopted for evaluating the final solution. Bevrani H. et al (2010) presented Reinforcement Learning Based Multi-agent LFC Design Concerning the Integration of Wind Farms. Frequency regulation in interconnected networks is 60

13 one of the main challenges posed by wind turbines in modern power systems. The wind power fluctuation negatively contributes to the power imbalance and frequency deviation. This paper presents an intelligent agent based load frequency control (LFC) for a multi-area power system in the presence of a high penetration of wind farms, using multi-agent reinforcement learning (MARL). Nonlinear time domain simulations on a 39-bus test power system are used to demonstrate the capability of the proposed control scheme. Chatterjee Kalyan (2010) presented Design of Dual Mode PI Controller for Load Frequency Control. The paper presents a new technique for the automatic generation control of interconnected power systems. The proposed technique is developed for designing the controller using the concept of dual-mode control in the PI controller such that the proportional mode is made active when the rate of change of the error is sufficiently larger than a specified limit otherwise switched to the integral mode. A digital simulation is used in conjunction with the Hooke-Jeeve s optimization technique to determine the optimum parameters (individual gain of proportional and integral controller) of the PI controller. The Integrated Square of the Error (ISE) performance index is considered to measure the appropriateness of the designed controller. Case studies justify that dual mode with optimized values of the gains improved the control performance than the commonly used Variable Structure System. Liu Xiangjie et al (2010) presented Load Frequency Control considering Generation Rate Constraints. Constrained generalized predictive algorithm is employed to load frequency control in this paper. Generation rate constraint (GRC) has been considered. Using the linearization modeling technique, this paper deals with load frequency control by multivariable generalized predictive control method to build Controlled Auto-Regressive Integrated Moving Average model (CARIMA) and obtain generalized predictive control algorithm for load frequency control of the two-area reheat power system. Results demonstrate the effectiveness of the proposed generalized predictive control algorithm. Siraj S. F. et al (2010), presented A Robust Adaptive Predictive Load Frequency Controller to compensate for Model Mismatch. The paper describes the design and implementation of a selftuning Load Frequency Controller (LFC) of a power system based on the Adaptive Generalized Predictive (AGP) controller. The application of predictive control in power system control is considered due to its ability to handle disturbances and un-modeled dynamics often encountered in interconnected power system environments. Simulation results show that the controller exhibits robustness in handling both problems with proper tuning of its parameters, especially when compared to the normal adaptive control methods of minimum variance and pole assignment. It has been observed that for the LFC system studied, the system with AGP 61

14 controller is always stable even in the presence of randomly varying or step disturbances as well as un modeled dynamics. Angel Molina-Garcia et al (2010) presented Decentralized Demand-Side Contribution to Primary Frequency Control. Frequency in large power systems is usually con-trolled by adjusting the production of generating units in response to changes in the load. As the amount of intermittent renewable generation increases and the proportion of flexible conventional generating unit decreases, a contribution from the demand side to primary frequency control becomes technically and economically desirable. One of the reasons why this has not been done was the perceived difficulties in dealing with many small loads rather than a limited number of generating units. Simulation results show that, using this approach, the demand side can make a significant and reliable contribution to primary frequency response while preserving the benefits that consumers derive from their supply of electric energy. Aidin Sakhavati et al (2011), presented Decentralized robust load-frequency control of power system based on quantitative feedback theory. This paper aims at investigating the problem of Load Frequency Control (LFC) in interconnected power systems in order to obtain robustness against uncertainties. A design method for a robust controller, based on Quantitative Feedback Theory (QFT), has been presented in this paper. For a two-area power system, the simulation results show that the system response with the proposed QFT controller exhibits transient response beyond PI controllers. It is also shown that the transient response of the tie line power can also be improved. Khodabakhshian A. et al (2012) presented Design of a robust load frequency control using sequential quadratic programming technique. This paper presents a new methodology, named Sequential Quadratic Programming (SQP), to design a robust PID controller for Load Frequency Control (LFC) of nonlinear interconnected power systems. The robust performance of the proposed controller is compared with that of a conventional PI controller, through the simulation of two multi-machine power system examples with a variety of disturbances. Results show that the proposed technique gives a better performance. Dey Rajeeb et al (2012), presented H load frequency control of interconnected power systems with communication delays. This paper considers the problem of power system load frequency control design incorporating the effect of using open communication network instead of a dedicated one for the area control error signals. To have this appropriately considered time delays in the ACE signals. A delay-dependent two-term H controller design has then been proposed using linear matrix inequalities. Comparison of effectiveness of the proposed two-term controller 62

15 with that of existing one-term and two-term controller designs establishes the superiority as well as applicability of the present design for the LFC problem. Parmar K.P. Singh et al (2012) presented Load frequency control of a realistic power system with multi-source power generation. In this paper, load frequency control (LFC) of a realistic power system with multi-source power generation is presented. In practice, access to all the state variables of a system is not possible and also their measurement is costly and difficult. Usually only a reduced number of state variables or linear combinations thereof, are available. To resolve this difficulty, optimal output feedback controller which uses only the output state variables is proposed. The sensitivity analysis reveals that the proposed controller is quite robust and optimum controller gains once set for nominal condition need not to be changed for ±25% variations in the system parameters and operating load condition from their nominal values Based on ANN Control Technique Bid A. P. et al (1994) presented An Enhanced Neural Network Load Frequency Control Technique. In this work it is continued to investigate the use of neural Network (NN) to act as the control intelligence in conjunction with a standard adaptive load frequency control scheme. In this approach a NN is operated in parallel with a full load frequency adaptive control &e. The NNs are able to monitor the system frequency as the controller issues control command. This neural control approach is shown to have several advantages over the basic fixed parameter schemes and the more advanced adaptive control technique that have been developed. The inherent stability and rapid ability to re configure the NN control strategy, to match the operation of the controlled system; will be more beneficial than other method. Shayeghi H. and H. A. Shayanfar (2004) presented Power System Load Frequency Control Using RBF Neural Networks Based on µ-synthesis Theory. This paper describes a nonlinear Radial Basis Function Neural Networks (RBFNN) controller based on µ-synthesis technique to load frequency Control (LFC) of the power systems. Power systems such as other industrial plant & have some uncertainties and deviations due to multivariable operating conditions and load variations that for controller design, had to take the uncertainties into account For this reason, in design of the proposed load frequency controller the idea of µ-synthesis theory is being used. Shayeghi Hossein and Heidar Ali Shayanfar (2004), presented Automatic Generation Control of Interconnected Power System Using ANN Technique Based on μ Synthesis. This paper presents a nonlinear Artificial Neural Networks (ANN) controller based on μ synthesis for Automatic Generation Control (AGC) of power systems. Power systems such as other industrial plants have some uncertainties and deviations due to multivariable operating conditions and load 63

16 changes. The simulation results on a two-area power system show that the proposed ANN controller is effective and gives good dynamic responses even in the presence of Generation Rate Constraints (GRC). In addition, it is superior to the conventional PI and μ based robust controllers. Shayeghi H., H.A. Shayanfar, O.P. Malik (2007), presented Robust decentralized neural networks based LFC in a deregulated power system. In this paper, a decentralized radial basis function neural network (RBFNN) based controller for load frequency control (LFC) in a deregulated power system is presented using the generalized model for LFC scheme according to the possible contracts. The results of the proposed controllers are compared with the mixed H 2 /H controllers for three scenarios of the possible contracts under large load demands and disturbances. Bhongade Sandeep et al (2011), presented Performance of SMES unit on Artificial Neural Network based Multi-area AGC scheme. This work investigates the performance of Superconducting Magnetic Energy Storage (SMES) unit on Artificial Neural Network (ANN) based multi-area AGC scheme. SMES units have been used to the power systems to inject or absorb active power. A three layer feed forward neural network (NN) is proposed for controller design and trained with Back propagation algorithm (BPA). The result shows that the performance of the ANN controller with SMES unit is better than the performance without SMES unit. Bhongade Sandeep et al(2011), presented Effect of SMES unit in load following contract in a restructured power system. The purpose of this paper is to analyze the effect of SMES unit on the Dynamic Neural Network (DNN) based multi area AGC scheme. The advantage of the DNN controller is that it does not require extensive and rigorous model for optimal tuning. It requires a set of training data. The training data can be generated from the system model. The result shows that the performance of the DNN controller with SMES unit is better than the performance without SMES unit Based on Fuzzy Control Technique Hiyama Takashi et al(2000), presented Fuzzy Logic Based Multi-Functional Load Frequency Control. This paper presents a multi-functional fuzzy logic based Tie- line Bias Control (TBC) scheme considering the MWh constraint for the power transmission on the tie-line and the regulation margin. In addition, the real power flow constraint on each trunk line is also taken into account. A detailed non linear LFC simulator has been developed in the Matlab/Simulink environment. Simulation results demonstrate the efficiency of both the proposed control scheme 64

17 and the simulator performance. By using the proposed fuzzy logic control scheme, the MWh constraint is satisfied to avoid the MWh contract violation. The regulation capacity is always kept to a certain level by the replacement of the required generation from the LFC units to the non-lfc units. Tyagi Barjeev and S.C. Srivatav (2003), presented A Fuzzy Logic Based Load Frequency Controller in a Competitive Electricity Environment. This paper presents the design of a fuzzy logic based controller for Automatic Generation control (AGC) in a deregulated electricity environment. A general model of the integral controller has been developed for multi-area system having poolco, bilateral and mixed transactions employing fuzzy logic scheme for optimal tuning of integral gain. The Area Control Error (ACE) signal and rate of change of the Area Control Error (Che ACE) have been used as input to the fuzzy logic based controller. Nanda J. and J. S. Sakkaram (2003), presented Automatic Generation Control with Fuzzy Logic Controller Considering Generation Rate Constraint. This paper describes application of Fuzzy Logic Controller (FLC) for Automatic Generation Control (AGC) of a two area reheat thermal power system. Different types of inputs for the FLC and different number of triangular Membership Functions (MF) are considered to examine their effect on the dynamic responses for the Automatic Generation Control (AGC) system. Nanda J. and A. Mangla (2004), presented Automatic Generation Control of an Interconnected Hydro-Thermal System Using Conventional Integral and Fuzzy Logic Controller. This paper deals with Automatic Generation Control of interconnected hydrothermal system in the continuous- discrete mode using conventional integral and fuzzy logic controllers. Effects of variation of sampling time period on dynamic responses have been investigated, both with conventional integral controller and fuzzy logic controllers, considering small step perturbations. Effects of different number of triangular membership functions and inputs for Fuzzy Logic Controller on dynamic response have been explored. Further, dynamic responses under small step perturbation have been compared, considering integral and fuzzy logic controllers. Presence of FLC in both areas and small step perturbation in either area or in both areas simultaneously provides better dynamic response than with conventional integral controller. Altas I. H. and J. Neyens (2006), presented A Fuzzy Logic Decision Maker and Controller for Reducing Load Frequency Oscillations in Multi-Area Power Systems. This paper deals with the application of a fuzzy logic based decision maker and controller in order to damp load-frequency oscillations in multi area power systems. A linearised dynamic model of a two area power system is derived from that of a well known single area system and combined with the proposed fuzzy controller for simulation purposes. The fuzzy logic based controller with a decision making unit 65

18 is designed to replace the classical integral type controllers. The proposed approach is compared with classical ones for performance and validity. Rao C. Srinivasa et al (2007), presented Automatic Generation Control of TCPS Based Hydrothermal System under Open Market Scenario: A Fuzzy Logic Approach. This paper presents the analysis of Automatic generation control (AGC) of a two-area interconnected thyristor controlled phase shifter (TCPS) based hydrothermal system in the continuous mode using fuzzy logic controller (FLC) under open market scenario. The effects of nonlinearities like dead band and generation rate constraint on the system have also been investigated. Simulation results show that the limitations of integral controller can be overcome by including Fuzzy concept and thereby the response of frequency and tie line power can be improved substantially following a load change in any area. Haider A.F. Mohamed et al (2008), presented Load frequency controller design for Iraqi National Super Grid System using Fuzzy logic controller. This paper presents a Fuzzy Gains Scheduled Proportional and Integral (FGPI) controller for Load Frequency Control (LFC) of the Iraqi National Super Grid system (INSGS). A linear-time-invariant mathematical model is derived for the system that consists of six generating stations with various types of turbines. Maintaining frequency of each area and the net tie-line power at scheduled value due to the load perturbations are considered in this study. Simulation of the proposed control scheme show better results and transient performance improvements when compared to the conventional method which is also simulated in this paper. El-Metwally K.A. (2008), presented An Adaptive Fuzzy Logic Controller for a Two Area Load Frequency Control Problem. This paper presents an adaptive fizzy logic control approach for designing a decentralized controller for load frequency control of interconnected power areas. The proposed adaptive fuzzy logic load frequency controller (AFLFC) has been designed to improve the dynamic performance of the frequency and the tie line power flow under a sudden load change in the power areas. The AFLFC replaces the original conventional integral controller and utilizes the same area criteria error input. The effect of generation rate constraint (GRC) for both areas has been considered in the controller design. Time domain simulations using MATALB/SIMULINK program has been performed to demonstrate the effectiveness of the proposed AFLFC. Aravindan P. and M.Y. Sanavullah (2009), presented Fuzzy Logic Based Automatic Load Frequency Control of Two Area Power System with GRC. This paper describes the Automatic Generation Control (AGC) of interconnected reheat thermal system using Proportional - Integral (PI) and extended Proportional-Integral (extended PI) and Fuzzy Logic Controller (FLC). The 66