Conventional Automatic Generation Control Research Articles

HFAGC based on MOPSO technique: Optimal design, comparison, verification

Good recovery of power system’s synchronism in the affected eclectic power system caused by the loading condition changes is the main target of Automatic Generation Control (AGC). Accomplished endeavors are led to suggest Hierarchical Fuzzy AGC (HFAGC) in multi-area interconnected power system aime d at alleviating both prominent issues i.e.: the low frequency power oscillations and the tie-line power exchange deviations. In this regard, application of multi-objective optimization technique isn’t avoidable. Due to high performance of Multi Objective Particle Swarm Optimization (MOPSO) in solving non-linear objectives, it has been engaged to unravel the optimization problem and optimal tune the HFAGC. To confirm the high efficiency and robustness of suggested controller, two different multi-area interconnected power systems have been taken into account for this study. Meantime, the potency of HFAGC has been thoroughly appraised and compared with Conventional AGC (CAGC) via occurrence of the Step Load Perturbation (SLP) in both these test power systems. To sum up, the simulations results have transparently corroborated the high performance of HFAGC as compared with CAGC in both the test power systems.

Optimal AGC regulator for multi-area interconnected power systems with parallel AC/DC links

AbstractThe problem of simultaneous tuning of the automatic generation control (AGC) regulator’s gains of multi-area interconnected power system is carried out in this manuscript. Based on the types of area interconnections, a power system model consisting of reheat turbines is investigated by two test cases for the AGC study. In one of the test case AC link is used as area interconnection, whereas the parallel combination of AC/DC links is used as area interconnection in other test case. Each test case control area is consisting of plants with reheat thermal turbines. Genetic algorithm (GA) is used to globally optimize the gains of proportional integral-based AGC regulators with simultaneous optimization of frequency bias coefficient and tie-line power flows. The dynamic response curves are obtained for various system states with the implementation of designed GA-based AGC regulators considering 1% load perturbation in one of the areas. The conventional AGC regulators are also developed using the popular...

Automatic generation control of multi source power generation under deregulated environment

Abstract This paper presents a novel scheme for automatic generation control (AGC) of interconnected two area multi source power generation under deregulated environment. The conventional two-area AGC system is modified to take into account the effect of bilateral contracts on the dynamics. In the considered two area power system, each area contains two GENCOs; first GENCO is a reheat steam turbine with appropriate generation rate constraint nonlinearity and second GENCO is a gas turbine generation. The performances of integral (I), proportional-integral (PI), integral-derivative (ID) and proportional-integral-derivative (PID) are evaluated for the proposed AGC system in the deregulated environment. The gain of the controllers and speed regulation parameters are optimised using differential evolution (DE) algorithm. Differential evolution algorithm is used because of its convergence superiority and easy to implement. The performance of DE algorithm applied to the proposed problem is compared with that of Genetic Algorithm (GA) to establish its optimisation superiority of the former.

Guest Editorial

This is an IET Renewable Power Generation Special Section from the 3rd IET Renewable Power Generation Conference that was held in Naples. There was a wide range of topics among which were wind (turbines, offshore wind farms),photovoltaic generation, distribution power systems including power conversion, management of energy by means of demand side management and energy storage taking into consideration power markets. More than 120 papers were included in the conference's technical programme, and the topics covered a broad spectrum within the field of renewable power generation. A selection of papers presented at the Naples conference were considered appreciable by the Conference Session Chairs and invited to submit to the IET Renewable Power Generation journal. After extensive peer review, two significant papers were accepted for publication by the Editor-in-Chief and the Associate Editor. The accepted papers cover both generation by renewable sources and distribution of the energy treating, in particular, aspects related to the integration of renewable sources in the grid and the control and management of a distributed generation network. K. Musasa, M. N. Gitau and R. C. Bansal, in their paper “Dynamic analysis of DC-DC converter internal to an offshore wind farm”, have analysed the automatic generation control (AGC) problem and considered it in interconnected power systems with doubly-fed induction generator (DFIG)-based wind turbines. A non-linear least squares support vector machines (LS-SVM)-based AGC regulator is proposed; this is trained from an off-line data set obtained from designing and implementing the robust controller to power a system under diverse operating conditions and area load changes. An investigation of time response plots reveal that the designed LS-SVM-based AGC regulator shows promising performance for power systems with governor dead-band non-linearity when compared to that obtained with multi-layer perceptron neural networks and conventional PI-based AGC regulators for a wide range of parametric uncertainties and area load disturbances occurring in the area of the power system. In their paper, M. Cresta, F. M. Gatta, A. Geri, M. Maccioni, A. Mantineo and M. Paulucci analyse possible strategies for the control and management of an LV network with distributed generation connected at LV (consisting in photovoltaic power plants equipped with the last generation of inverters) and electric vehicles charging stations (EVCSs). Various possible scenarios have been studied: the LV network as actually operated; the network operated with the EVCS and the network operated with the EVCS and the NAS storage system. The evolution of voltage levels at the LV busbar, of power-factors at the secondary substation and of energy losses in the LV network have been calculated. By analysing the results, it was found that the installation of the EVCS itself does not present any criticality for the considered distribution network. A proposed optimal power flow detects optimal strategies for the management of reactive power flow supplied by the PV inverter and for the control of charge/discharge cycles of the NAS. From an economic point of view, the installation of the NAS appears to be unjustifiable because of both the high investment cost and the increase in operating costs (due to the additional energy losses). Lastly, the “demand response” practice, applied to “secondary substation” customers does not provide significant benefits on the network operation. However, this practice may generally constitute a convenient and effective solution for the implementation of the “load shifting” along a daily load diagram.

Fuzzy Logic and Genetic Algorithm based Automatic Generation Control of Two-Area Deregulated Power Systems

This paper illustrates the automatic generation control (AGC) of an interconnected two-area power system under deregulated environment. Two controllers viz., a Hybrid Fuzzy-PI (HFPI) controller and Genetic Algorithm based PI (GAPI) controller are proposed to improve the dynamic response of the power systems. The conventional two-area AGC system is modified to take into account the effects of bilateral contracts on the dynamics. In the HFPI controller, the parameters of the conventional PI controller are modified according to the principles of fuzzy logic whereas in GAPI controller, tuning parameter design criteria is reformulated as an optimization problem and the general rules of genetic algorithm (GA) are applied. The convergence and performance of the system are studied for different operating cases and a comparison among conventional integral (CI) controller, HFPI controller and GAPI controller are presented. The simulation results show that the HFPI controller proposed in this paper perform better than the conventional integral and GAPI controllers in terms of settling time and overshoot.

Distributed Automatic Generation Control Using Flatness-Based Approach for High Penetration of Wind Generation

To allow for high penetration of distributed generation and alternative energy units, it is critical to minimize the complexity of generator controls and the need for close coordination across regions. We propose that existing controls be replaced by a two-tier structure of local control operating within a global context of situational awareness. Flatness as an extension of controllability for nonlinear systems is a key to enable planning and optimization at various levels of the grid in this structure. In this study, flatness-based control for automatic generation control (AGC) of a multi-machine system with high penetration of wind energy is investigated. The local control tracks the reference phase which is obtained through economic dispatch at the global control level. As a result of applying the flatness-based method, the n machine system is decoupled into n linear controllable systems in canonical form. Therefore, the control strategy results in a distributed AGC formulation which is significantly easier to design and implement compared to conventional AGC. Practical constraints such as generator ramping rates can be considered in designing the local controllers. The proposed strategy demonstrates promising performance in mitigating frequency deviations and the overall structure could facilitate operation of other nontraditional generators.

Automatic generation control scheme for frequency linked price signal followed in India

Indian electricity market has adopted a concept of frequency linked commercial tariff system, commonly referred to as availability-based tariff (ABT), where variation in system frequency is used as market signal to encourage utilities to change generation in real time operation. As frequency varies with real power imbalance, proper incentive is rewarded for automatic generation control (AGC) service provided by the generating utility for making up the real power mismatch. In ABT, the rate of unscheduled interchange (RUI) for AGC service is fixed depending upon the frequency condition prevailing at that time. The conventional AGC system though tries to bring the frequency error to zero but it would be an ineffective solution for participating generating utilities under ABT since incentive/penalty varies with frequency. This paper investigates the rules and advocacy of ABT more strategically and develops a model for AGC based on conventional if-then logics for load-frequency regulation scheme that will respond to the frequency-based price signal in a profitable manner. The proposed model is tested on IEEE 14 bus system and part of northern region grid of India.

Real-Time Central Demand Response for Primary Frequency Regulation in Microgrids

Providing ancillary services for future smart microgrid can be a challenging task because of lack of conventional automatic generation control (AGC) and spinning reserves, and expensive storage devices. In addition, strong motivation to increase the penetration of renewable energy in power systems, particularly at the distribution level, introduces new challenges for frequency and voltage regulation. Thus, increased attention has been focused on demand response (DR), especially in the smart grid environment, where two-way communication and customer participation are part of. This paper presents a comprehensive central DR algorithm for frequency regulation, while minimizing the amount of manipulated load, in a smart microgrid. Simulation studies have been carried out on an IEEE 13-bus standard distribution system operating as a microgrid with and without variable wind generation. Simulation results show that the proposed comprehensive DR control strategy provides frequency (and consequently voltage) regulation as well as minimizing the amount of manipulated responsive loads in the absence/presence of wind power generation.

Advanced Automatic Generation Control with Automatic Compensation of Tie-Line Losses

This article proposes the improvement of present-day common automatic generation control schemes by the simple addition of area tie-line loss compensation to the standard conventional control algorithm. Conventional automatic generation control regulators of interconnected power systems are developed, assuming the same tie-line power flows on both tie-line terminals. This assumption has the systematic (steady-state) output errors on controlled variables: the system frequency (and indirectly on the synchronous time) and areas tie-line exchanges. To eliminate large deviations of these variables outside of prescribed limits, their periodical corrections are necessary. This is achieved by simple modification of classical automatic generation control regulators, with the addition of corresponding tie-line losses to the area control error signal on standard automatic generation control regulator inputs. With such a modification, area automatic generation control regulators would attain better control performance, with less frequent operation switching from normal to the corrective mode. In addition, they become able to share tie-line power losses to interested parties by a simple adjustment of agreed participation coefficients set on corresponding automatic generation control regulators. The benefits obtained by such modified automatic generation control are paid by one additionally needed remote measurement per tie-line from their terminals in neighboring areas, while all other elements of existing automatic generation control schemes remain unchanged.

Load following in a bilateral market with local controllers

In this paper, the conventional Automatic Generation Control (AGC) of two-area interconnected power system is modified to take into account the effect of bilateral contracts between the supplier and customer. A load following controller on each generator involved in the bilateral contract is considered. A separate control scheme for generators taking part in load-following is proposed to share the uncontracted power demanded by some customers. Simulation studies show that both the control schemes are very effective for the generators taking part in load following.

Performance evaluation of evolutionary designed conventional AGC controllers for interconnected electric power system studies in a deregulated market environment

Electric power industry is currently in transition from vertically integrated utilities to an industry that will incorporate competitive companies. This increases the complexity of the load frequency issue and calls for more insight and research. In this context, the tuning of a multi-area automatic generation control (AGC) system after deregulation and furthermore, the effect of reheat turbines dynamics in the power system performance, are not yet discussed in depth and are studied in this work. The effect of bilateral contracts on the dynamics of the system is taken into account and the concept of DISCO participation matrix for these bilateral contracts is simulated. Genetic algorithms are adopted in order to obtain the optimal parameters of the load-frequency controllers as well as of the frequency biases of thermal systems with reheat turbines. Also, since the optimum parameter values of the classical AGC have been obtained in the literature by minimizing the popular integral of the squared errors criterion (ISE) only, an effort is made in this study to show that this criterion does not give always the best system performance especially in a deregulated environment. In this work, we investigate the optimum adjustment of the load frequency controllers using a set of performance indices which are various functions of error and time. In this way, someone can observe the various performances that such a kind of power system might have when a different performance index is used. It should be noted that to the extent of the authors' knowledge, this kind of optimization has not been done yet in the literature. The performances of the tuned two–area AGC system are obtained using appropriate Matlab/Simulink models. Finally, it is envisaged that the synthesis procedure highlighted in this paper could be of practical significance for tuning conventional AGC controllers for an interconnected thermal-electric power system in a deregulated environment. Keywords: AGC, load frequency control, power systems, deregulation, bilateral contracts, genetic algorithms

Automatic correction of the systematic error on AGC regulators due to tie‐line losses

AbstractThis paper considers the problems of automatic correction of systematic error appearing in conventional Automatic Generation Control (AGC) regulators, due to the ignorance of power losses, normally existing on all inter‐area tie‐lines. This is achieved with modification of input signals on AGC area regulators (the Area Control Error, ACE) by introducing the tie‐line losses, calculated by simple measurements of all area tie‐line flows at both (sending and receiving) line ends. The paper presents the theoretical development of the idea and proposes the new, modified, but cheap AGC scheme, proven by simulation tests on the example of two‐area interconnection. The benefit of applying the proposed AGC regulators is the better system performance and less frequent need for the synchronous time and inadvertent interchange error corrections. Copyright © 2007 John Wiley & Sons, Ltd.

GA application to optimization of AGC in three-area power system after deregulation

In this paper, genetic algorithm (GA), which is used for optimization of integral gains and bias factors, is applied to automatic generation control (AGC) in three-area power system after deregulation. The conventional three-area AGC system is modified to take into account the effect of bilateral contracts on the dynamics. In the considered power system, each area contains two GENCOs; GENCOs at the first and the second areas include steam turbines and GENCOs at the third area include hydro turbines as generating units. After deregulation, to describe bilateral contract for three-area AGC, DISCO participation matrix is used. The performance of the system is studied for different operating cases, in terms of the conventional controller gains and bias factors optimized using real coded GA.

AGC simulator for price-based operation. I. A model

This paper deals with automatic generation control (AGC) in a deregulated electric industry. Through the passage of new public utility regulatory policies, the Federal Energy Regulatory Commission (FERC) encourages an open market system for price based operation. The FERC has issued a notice of proposed rulemaking seeking comments on various ancillary services. One of these ancillary services is load following. This paper suggests the modifications required in the conventional AGC software to prepare students to study load following in price-based market operation. The details of implementing an academic power system are used to highlight the differences between the AGC operation in a vertically integrated industry (conventional paradigm) and a horizontally integrated industry (new paradigm). The future business environment for electric utilities is incompletely defined as of this writing. Therefore, a framework for price-based operation is developed to assist students in understanding AGC implementation in the new market structure. The proposed market structure is kept generic enough to capture all possibilities in marketing load following capability.

AGC simulator for price-based operation. II. Case study results

For pt.I see ibid., vol.12, no.2, p.527-32 (1997). This paper deals with an automatic generation control (AGC) problem in a deregulated industry. Through the passage of new public utility regulatory policies, the Federal Energy Regulatory Commission (FERC) encourages an open market system for price based operation. The FERC has issued a notice of proposed rulemaking seeking comments on various ancillary services. One of these ancillary services is load following. Part I describes the simulation models and software implementation of load following contracts in the new environment, and also developed a framework for new market structure to understand AGC implementation in the price-based operation. This paper reviews the case studies to show the modifications required of conventional AGC software for the new environment. Three sets of case study results are reported. The first and second case studies illustrate how to simulate bilateral and poolco based transactions respectively in the new market place. The third case study considers various (bilateral and poolco based) contracts existing simultaneously in the system. The simulation results illustrate that the tie-line flows due to increased number of various contracts will tend to cancel among each other.

Optimal AGC tuning with genetic algorithms

This paper deals with the application of genetic algorithms for optimizing the parameters of conventional automatic generation control (AGC) systems. A two-area nonreheat thermal system is considered to exemplify the optimum parameter search. A digital simulation is used in conjunction with the genetic algorithm optimization process. Several integral performance indices, or cost functions, are considered in the search for the optimal AGC parameters. The work is further extended to include the use of more elaborate feedback control strategies, such as the proportional-plus-integral type, within the decentralized frame. The results reported in this paper have not been obtained before and they demonstrate the effectiveness of the genetic algorithms in the tuning of the AGC parameters.

ACTIVE AND REACTIVE POWER FLOW FOR MULTIAREA SYSTEMS ON AUTOMATIC GENERATION CONTROL IN THE PRESENCE OF RAPIDLY CHANGING LOADS

ABSTRACT In this paper, the control area dynamics of power systems on automatic generation control are revisited. The role of reactive power flow between regions under automatic generation control is studied by review of simulations in which the reactive power flow is modeled/not modelled. The effect of transmission line loading is also studied. Reactive power control is accomplished in part by automatic voltage regulation, and reactive power resides in a control “loop” much in the same way as active power resides in conventional automatic generation control. An important observation of the analysis is that short term phenomena (e.g., peaks in tie line flow after a load disturbance ΔP = j ΔQ) require the reactive loop in the model in order to obtain accurate response. Long term phenomena are less sensitive to reactive power modelling. Although these observations are well known qualitatively, examples in this paper help to quantify the role of reactive power in power flow dynamics. The main lesson learned is that there are cases in which reactive power flow must be modelled in order to accurately study active power control and flow. An emphasis in the paper is rapidly changing, heavy industrial loads. The multiarea case is considered.

Automatic generation control: Decentralized area-wise optimal solution

A decentralized scheme is proposed for the design of automatic generation control (AGC) for interconnected power systems. This scheme uses the natural structural properties of interconnected power systems and gives a new method for decentralized AGC regulator design, using the existing theory of proportional-plus-integral linear regulators applied to each individual power area. It is shown that a decentralized design, based upon the expansion-contraction theory of large-scale systems with overlapping and modified linear regulators with incomplete subsystem feedback, is suitable to handle the design of AGC regulators for present-day interconnected power systems. The resulting AGC retains the autonomous area control concept and load distribution property of conventional AGC regulators, while at the same time allows for improved transients and stability margins for interconnected areas. The application of this decentralized AGC scheme is illustrated on a 17th-order model of a two-area interconnected power system.