An attempt is made in This work to present critical literature review and an up-to-date and exhaustive bibliography on the AGC of power systems. Various control aspects concerning the AGC problem have been highlighted. AGC schemes based on parameters, such as linear and nonlinear power system models, classical and optimal control, and centralized, decentralized, and multilevel control, are discussed. AGC strategies based on digital, self-tuning control, adaptive, VSS systems, and intelligent/soft computing control have been included. Finally, the investigations on AGC systems incorporating BES/SMES, wind turbines, FACTS devices, and PV systems have also been discussed.

Recent philosophies of automatic generation control strategies in power systems

Power System Oscillations.- Linear Control in Power Systems.- Test System Model.- Power System Stabilizers.- Multiple-Model Adaptive Control Approach.- Simultaneous Stabilization.- Mixed-Sensitivity Approach Using Linear Matrix Inequalities.- Normalized ?? Loop-Shaping Using Linear Matrix Inequalities.- ?? Control For Time-Delayed Systems.

Robust Control in Power Systems

The authors describe what automatic generation control (AGC) might be expected to do, and what may not be possible or expedient for it to do. The purposes and objectives of AGC are limited by physical elements involved in the process and, hence, the relevant characteristics of these elements are described. For reasons given, it is desired that AGC act slowly and deliberately over tens of seconds or a few minutes. From a perspective of utility operations, there is no particular economic or control purpose served by speeding up the AGC action. >

Understanding automatic generation control

A survey is presented of papers and reports that address various aspects of economic dispatch. The time period considered is 1977-88. Four related areas of economic dispatch are identified and papers published in the general areas of economic dispatch are classified into these. These areas are: optimal power flow, economic dispatch in relation to AGC, dynamic dispatch, and economic dispatch with nonconventional generation sources. >

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A review of recent advances in economic dispatch

The growing costs of fuel and operation of power generating units warrant improvement of optimization methodologies for economic dispatch (ED) problems. The practical ED problems have non-convex objective functions with equality and inequality constraints that make it much harder to find the global optimum using any mathematical algorithms. Modern optimization algorithms are often meta-heuristic, and they are very promising in solving nonlinear programming problems. This paper presents a novel approach to determining the feasible optimal solution of the ED problems using the recently developed Firefly Algorithm (FA). Many nonlinear characteristics of power generators, and their operational constraints, such as generation limitations, prohibited operating zones, ramp rate limits, transmission loss, and nonlinear cost functions, were all contemplated for practical operation. To demonstrate the efficiency and applicability of the proposed method, we study four ED test systems having non-convex solution spaces and compared with some of the most recently published ED solution methods. The results of this study show that the proposed FA is able to find more economical loads than those determined by other methods. This algorithm is considered to be a promising alternative algorithm for solving the ED problems in practical power systems.

Firefly Algorithm for solving non-convex economic dispatch problems with valve loading effect

A maiden attempt is made to explore the feasibility of developing an approach to solve the economic emission load dispatch (EELD) problem with line flow constraints using a classical technique based on co-ordination equations. The inability of the classical technique to handle the line flow constraints so far is circumvented innovatively by expressing the line flows in terms of active power generations through distribution factors. These distribution factors are elegantly developed from existing load flow information using a perturbation technique

Economic emission load dispatch with line flow constraints using a classical technique

An attempt is made to explore the feasibility of developing an approach to solve the power system economic emission load dispatch (EELD) problem with line flow constraints using a classical technique based on co-ordination equations. The inability of the classical technique to handle the line flow constraints so far is circumvented innovatively by expressing the line flows in terms of active power generations through distribution factors. These distribution factors are elegantly developed from existing load flow information using a perturbation technique. The proposed model based on the classical technique for EELD is tested on IEEE 14- and 30-bus test systems and the results are compared with those obtained by quadratic programming, the Hessian method, the Ricochet gradient method and the linear programming method.

Most of the work reported in the literature pertaining to Automatic Generation Control (AGC) of interconnected power systems is centered around tie-line frequency bias control strategy. Supplementary controllers are designed to regulate the area control errors to zero effectively. Several modern design techniques have been used to optimize the parameters of the supplementary controllers. Supplementary controllers regulate the generation to match the load variation. As the generation change chases the load variation, the frequency and tie-power deviate from the scheduled values. This would result in accumulations of time error and inadvertent interchange. They would also occur due to various measurement errors or intentional offsets in scheduled settings. It is expected that individual areas will make all reasonable efforts to minimize time error and inadvertent interchange accumulations by minimizing or eliminating source causes. There is a need for correcting these accumulations. Such corrections are achieved by making appropriate offsets in system frequency schedules to compensate for time error accumulations and offsets in area net interchange schedules to compensate for inadvertent interchange accumulations. Detailed literature survey clearly shows that the two-step correction scheme, mentioned above, has been used by utilities inspite of some practical difficulties. To avoid those difficulties they are looking forward for a suitable control strategy that not only maintains constancy of system frequency and desired tie-power flow but also achieves zero steady state time error and inadvertent interchange. It is essentially in this area, the investigations are carried out in this paper.

Discrete-mode automatic generation control of a two-area reheat thermal system with new area control error

The paper deals with some aspects of automatic generation control of the two-area hydrothermal system provided with classical controllers. A comprehensive procedure for continuous-and discrete-mode optimisation of integral controllers using an integral squared error criterion is suggested. Investigations reveal that the optimal integral gains achieved through continuous-mode analysis are totally unacceptable in the discrete mode for the sampling periods used in practice. Moreover, for all practical purposes, the optimum integral gains in the discrete mode can be achieved by neglecting the generation rate constraints from the mathematical model, in contrast to the case in the continuous mode. Analysis also highlights significant differences in the dynamic performance of the hydrothermal system due to step-load perturbation in either of the areas. An attempt is also made to recommend an optimum sampling period.

Automatic generation control of an interconnected hydrothermal system in continuous and discrete modes considering generation rate constraints

Summary form only given as follows. This paper presents a new approach for real-time tuning the parameters of a conventional power system stabilizer (PSS) using a radial basis function (RBF) network. The RBF network is trained using an orthogonal least squares (OLS) learning algorithm. Investigations reveal that the required number of RBF centers depends on spread factor, /spl beta/ and the number of training patterns. Studies show that a parsimonious RBF network can be obtained by presenting a relatively smaller number of training patterns, generated randomly and spreadover the entire operating domain. Investigations reveal that the dynamic performance of the system with an RBF network adaptive PSS (RBFAPSS) is virtually identical to that of an artificial neural network based adaptive PSS (ANNAPSS). The dynamic performance of the system with RBFAPSS is quite robust over a wide range of loading conditions and equivalent reactance X/sub c/.

M.L. Kothari

Papers

Economic emission load dispatch with line flow constraints using a classical technique

Economic emission load dispatch with line flow constraints using a classical technique

Discrete-mode automatic generation control of a two-area reheat thermal system with new area control error

Automatic generation control of an interconnected hydrothermal system in continuous and discrete modes considering generation rate constraints

Radial basis function (RBF) network adaptive power system stabilizer