Showing papers in "Electric Power Components and Systems in 2008"
TL;DR: Various distribution system load flow algorithms, based on the forward/backward sweeps, are reviewed, and their convergence ability is quantitatively evaluated for different loading conditions, R/X ratios, and sub-station voltage levels.
Abstract: Because of different characteristic features of distribution networks, such as radial structure and high R/X ratio, distribution system load flow analysis differs significantly from transmission systems. Accordingly, a number of methods that are specially designed for the solution of the power flow problem in radial distribution systems are found in the literature. Most of the developed methods are based on the forward/backward sweep processes for the solution of the ladder networks. In this article, various distribution system load flow algorithms, based on the forward/backward sweeps, are reviewed, and their convergence ability is quantitatively evaluated for different loading conditions, R/X ratios, and sub-station voltage levels. Moreover, the effects of static load modeling on the convergence characteristics of algorithms are also investigated.
167 citations
TL;DR: In this paper, the authors present an approach to solve the dynamic economic dispatch (DED) problem, including valve-point effects, using the differential evolution (DE) algorithm.
Abstract: This article presents the novel and efficient approach to solve the dynamic economic dispatch (DED) problem, including valve-point effects. The DED problem is an optimization problem with an objective to determine the optimal combination of power outputs for all committed generating units over a certain period of time in order to minimize the total fuel cost while satisfying dynamic operational constraints and load demand in each interval. The differential evolution (DE) algorithm is a powerful evolutionary algorithm for global optimization in real problems. In the proposed approach, the conventional economic load dispatch, for each time interval in a forward and reverse sequence, is independently performed using the DE algorithm with suitable modifications of the generation limits of the units due to the ramp-rate constraints of the generators. A certain load profile requires the traditional DED for a given set of committed units is determined by checking each interval in the scheduling horizon ...
104 citations
TL;DR: In this paper, a static synchronous series compensator (SSSC)-based damping controller is investigated for power system stability improvement by minimizing a timedomain-based objective function, in which the deviation in the oscillatory rotor speed of the generator is involved.
Abstract: Power-system stability improvement by a static synchronous series compensator (SSSC)-based damping controller is thoroughly investigated in this article. The design problem of the proposed controller is formulated as an optimization problem, and the particle swarm optimization technique is employed to search for the optimal controller parameters. By minimizing a time-domain-based objective function, in which the deviation in the oscillatory rotor speed of the generator is involved, stability performance of the system is improved. The performance of the proposed controller is evaluated under different disturbances for both a single-machine infinite-bus power system and a multi-machine power system. Results are presented to show the effectiveness of the proposed controller. It is observed that the proposed SSSC-based controller provides efficient damping to power-system oscillations and greatly improves the system voltage profile under various severe disturbances. Furthermore, the simulation result...
91 citations
TL;DR: In this paper, a new approach based on a constrained PS algorithm was proposed to solve various types of power system economic load dispatch (ELD) problems, such as ELD with valve point (EDVP) effects, multi-area ELD, companied economic-environmental dispatch, and cubic cost function economic dispatch.
Abstract: Direct search (DS) methods are evolutionary algorithms used to solve constrained optimization problems. DS methods do not require information about the gradient of the objective function when searching for an optimum solution. One such method is a pattern search (PS) algorithm. This study presents a new approach based on a constrained PS algorithm to solve various types of power system economic load dispatch (ELD) problems. These problems include economic dispatch with valve point (EDVP) effects, multi-area economic load dispatch (MAED), companied economic-environmental dispatch (CEED), and cubic cost function economic dispatch (QCFED). For illustrative purposes, the proposed PS technique has been applied to each of the above dispatch problems to validate its effectiveness. Furthermore, convergence characteristics and robustness of the proposed method has been assessed and investigated through comparison with results reported in literature. The outcome is very encouraging and suggests that PS methods may be very efficient when solving power system ELD problems.
74 citations
TL;DR: The development of an automatic fault data generation model using PSCAD and its application for training and testing of SVMs is developed and it is observed that an SVM with an RBF kernel provides better fault classification accuracy than that of an S VM with polynomial kernel.
Abstract: This article presents a new approach for fault classification in a two-terminal overhead transmission line using a support vector machine classifier. Wavelet transform is used for the decomposition of measured signals and for extraction of the most significant features (feature extraction), which facilitates training of the SVM, particularly in terms of getting better classification performance (high accuracy). After extracting useful features from the measured signals, a decision of fault or no-fault on any phase or multiple phases of a transmission line is carried out using three SVM classifiers. The ground detection task is carried out by a proposed ground index. Two kernel functions—polynomial and Gaussian radial basis function (RBF)—have been used, and performances of classifiers have been evaluated based on fault classification accuracy. In order to determine the optimal parametric settings of an SVM classifier (such as the type of kernel function, its associated parameter, and the regulari...
65 citations
TL;DR: Particle swarm optimization has emerged as a useful optimization tool for handling non-linear programming problems and various modifications to the basic method have been proposed with a view to enhance speed and robustness.
Abstract: Particle swarm optimization (PSO) has emerged as a useful optimization tool for handling non-linear programming problems. Various modifications to the basic method have been proposed with a view to enhance speed and robustness. This method has been applied successfully on some benchmark mathematical problems. A few PSO applications have been reported on real-world problems, such as network reconfiguration for loss reduction, load balancing, and even capacitor placement in distribution systems being discrete in nature. PSO is modified to discrete particle swarm optimization (DPSO). The results of DPSO are compared with the results of the genetic algorithm.
54 citations
TL;DR: The structures and operating principles are described first, and then the end-effect in the stator permanent magnet machines is investigated by a 3-D calculation, and a leakage factor reflecting end- effect is defined to modify the 2-D predicted results.
Abstract: This article investigates the static characteristics of both doubly-salient brushless machines having magnets in stator, namely the flux-switching permanent magnet machine (three-phase topology) and doubly-salient permanent magnet machines (including three-phase and two-phase structures), especially taking the influence of end-effect into account. The structures and operating principles are described first, and then the end-effect in the stator permanent magnet machines is investigated by a 3-D calculation, and a leakage factor reflecting end-effect is defined to modify the 2-D predicted results. The proposed approach is validated experimentally for the prototype machines.
41 citations
TL;DR: In this article, a hybrid energy system combining solar photovoltaic and wind turbine as a small-scale alternative source of electrical energy where conventional generation is not practical is proposed.
Abstract: This article proposes a hybrid energy system combining solar photovoltaic and wind turbine as a small-scale alternative source of electrical energy where conventional generation is not practical. A simple and cost-effective control technique has been proposed for maximum power point tracking from the photovoltaic array and wind turbine under varying climatic conditions without measuring the irradiance of the photovoltaic or the wind speed. The proposed system is attractive because of its simplicity, ease of control, and low cost. A complete description of the proposed hybrid system, along with detailed simulation results that ascertain its feasibility, are given to demonstrate the availability of the proposed system in this article. Simulation of the hybrid system under investigation was carried out using PSIM software.
41 citations
TL;DR: The proposed differential evolution algorithm to solve the unit commitment problem with ramp constraints shows competitive performance with the best of the similar methods proposed earlier.
Abstract: This article proposes a differential evolution algorithm to solve the unit commitment problem with ramp constraints. Two implementations of the proposed algorithm—the first one using the binary code, and the second one using the integer code—have been developed. Both of these implementations have been found to converge to the same optimum solution requiring a different number of generations and a different CPU time. The proposed algorithm shows competitive performance with the best of the similar methods proposed earlier.
41 citations
TL;DR: In this paper, the authors present 25 subjects, propose an index system, and discuss special issues for system operation reliability assessment, including probabilistic simulations of system dynamics, various operation measures and remedial actions in different timescales, and special requirements in input data and computing speed.
Abstract: Although considerable efforts have been devoted to reliability evaluation methods for power system planning in past years, very limited research work has been done for the probabilistic reliability assessment of power system operations. There are fundamental differences between reliability assessments for system planning and operations. After introducing the basic concepts, this article presents 25 subjects, proposes an index system, and discusses special issues for system operation reliability assessment. The major challenges in this area include probabilistic simulations of system dynamics, various operation measures and remedial actions in different timescales, and special requirements in input data and computing speed. The probabilistic reliability assessment of power system operations is an important task for power system researchers and engineers today and in the future.
38 citations
TL;DR: In this paper, the effect of voltage and frequency variation on the power output of the stall-and pitch-regulated fixed speed as well as the variable-speed wind-turbine generators was investigated.
Abstract: This article presents a study of the effect of voltage and frequency variation on the power output of the stall- and pitch-regulated fixed speed as well as the variable-speed wind-turbine generators (WGs). This study has been carried out using the steady-state model of each of these types of WGs. Each of these models facilitates the computation of the power output of the corresponding WG for a given voltage and frequency, considering the steady-state characteristics of the wind turbine, generator, and the controllers (where present). Simulation studies have been carried out to investigate the impact of frequency variation at nominal voltage and also the combined voltage and frequency variation.
TL;DR: In this paper, the rotor inertia is used as an energy storage component to mitigate the power fluctuations of wind turbines, and the proposed method is also modified to obtain better energy capturing efficiency.
Abstract: Due to wind speed variations, the output power of wind turbines fluctuates. This power fluctuation can cause frequency deviations and power outage, particularly when wind power penetration is significant. Energy storage devices, such as batteries, ultracapacitors, super inductors, and flywheels can be utilized in a hybrid system to solve this problem. These methods are effective, but they impose a significant additional cost to the system. This article presents a novel control method to mitigate the power fluctuations using the rotor inertia as an energy storage component. Therefore, the additional energy storage system is not required. The proposed method is also modified to obtain better energy capturing efficiency. The efficiency of the algorithm is evaluated based on developed equations. The energy extracting capability using this method is comparable to other methods such as the maximum power extraction algorithm. Simulation studies for various cases are performed on a permanent magnet synch...
TL;DR: In this article, the authors compared the performance of a low-speed doubly salient permanent magnet machine with a low speed flux-reversal machine for direct drive applications, using a genetic algorithm combined with the finite element method.
Abstract: The subject of this article is to optimize the design and to compare the performances of a low-speed doubly salient permanent magnet machine with those of a low-speed flux-reversal machine devoted to direct drive applications. The optimization, focused on the maximization of the machines mass-to-torque ratio, is done by a genetic algorithm combined with the finite-element method (FEM). The electromagnetic characteristics of the two optimized machines, including phase flux linkage, inductances, back-electromotive forces (EMFs), and static torque, obtained from FEM analysis, are then analyzed and compared. Finally, the torque cost and the torque density of the two machines are compared with those of other topologies.
TL;DR: In this article, a comprehensive study of the effect of the HNN parameters on the solution quality of the economic dispatch problem (EDP), as a case study, has been made.
Abstract: This article introduces some modifications to the conventional Hopfield neural network (HNN) to enhance its performance. A comprehensive study of the effect of the HNN parameters on the solution quality of the economic dispatch problem (EDP), as a case study, has been made. By investigating the describing curves, the best values for the HNN parameters are tuned. To further improve the solution quality, an adaptive correction factor is proposed and introduced to the EDP solution obtained by the HNN. To investigate the effect of the modifications on the solution quality of the EDP, three case studies are selected and solved. Comparisons of results are then made with others to prove the validity and effectiveness of the proposed modifications.
TL;DR: This article presents hybrid evolutionary programming, particle swarm optimization, and sequential quadratic programming methods to solve the dynamic economic dispatch problem (DEDP) of generating units considering non-convex features.
Abstract: This article presents hybrid evolutionary programming (EP), particle swarm optimization (PSO), and sequential quadratic programming (SQP) methods to solve the dynamic economic dispatch problem (DEDP) of generating units considering non-convex features. The non-convex feature considered is the valve-point effects, which is modeled in two different representations in the DEDP formulation. The proposed method is a two-phase optimizer. In the first phase, the candidates are treated by both the EP and PSO techniques to explore the solution space freely. In the second phase, the SQP method will be invoked when there is an improvement of solution (a feasible solution) in the first phase of the run. This hybrid optimization mechanism leads a better performance of the solution algorithm to effectively search the complex solution space. To validate the effectiveness of the proposed method, several non-convex DEDP test systems are studied and shown in general.
TL;DR: In this article, a smoothed wind-farm output power command is determined by wind condition and fuzzy neural network to reduce output power fluctuation of wind farms, and individual wind turbine generators are controlled by output power commands derived from wind-power command and coordination control for each wind turbine generator.
Abstract: There are concerns in regards to wind power generation as its output constantly, as well as considerably, varies. This article presents a control strategy for wind farms consisting of a wind turbine with variable pitch. In order to reduce output power fluctuation of wind farms, smoothed wind-farm output power command is determined by wind condition and fuzzy neural network. In addition, individual wind turbine generators are controlled by output power command derived from wind-farm output power command and coordination control for each wind turbine generator. Simulation results using an actual detailed model for wind-farm systems show the effectiveness of the proposed method.
TL;DR: In this paper, the authors proposed an enhanced method by reducing the number of unknown variables in the Newton-Raphson solution process, thus, much simpler and more computationally efficient.
Abstract: When transmission line parameters are not known, a two-terminal algorithm has been proposed in the past for pinpointing the fault location by utilizing voltage and current measurements during the fault. This article puts forth an enhanced method by reducing the number of unknown variables in the Newton-Raphson solution process. The new method is, thus, much simpler and more computationally efficient. In addition, a non-iterative fault location method that is feasible for all types of faults is developed. We have employed the electromagnetic transients program simulation studies to evaluate the performance of the approaches and have obtained quite encouraging results.
TL;DR: In this paper, a direct voltage control scheme was proposed to synchronize doubly-fed induction generators (DFIGs) to the grids. But the scheme requires less computational power and needs less tuning parameters, as compared with existing synchronization methods.
Abstract: This article delivers a novel direct voltage control scheme to synchronize doubly-fed induction generators (DFIGs) to the grids. The proposed scheme controls the stator terminal voltage of the DFIG, with the rotor converter operating at a constant frequency to track the grid voltage. The scheme requires less computational power and needs less tuning parameters, as compared with existing synchronization methods. The advantage of the proposed synchronization methodology is the minimization of possible transients that might arise when the DFIG is directly connected to the busbars without synchronization. Computer simulation and experimental results are presented to demonstrate the merits of the scheme.
TL;DR: In this article, a mathematical model of ultrasonic motors for speed control, which includes the nonlinearity and approximation of the dead-zone in control input, is presented, and the proposed speed model has been validated by experimental results.
Abstract: In this article, a mathematical model of ultrasonic motors for speed control, which includes the non-linearity and approximation of the dead-zone in control input, is presented. The intrinsic properties of ultrasonic motors (high torque for low speed, high static torque, compact in size, etc.) offer great advantages for industrial applications. However, the speed property of ultrasonic motors has a strong non-linear property as well as the dead-zone effect in control input associated with load torque. These properties present serious problems for accurate speed control. This article presents a mathematical model represented by a sinusoidal function, which includes these properties. The model is simple and has good approximation of the non-linearity and time varying properties. The proposed speed model has been validated by experimental results.
TL;DR: This article attempts to compare PI, fuzzy, and ANN controllers that are implemented in an embedded system for closed-loop speed control of DC drive fed by a buck-type DC–DC power converter and shows that ANN speed controllers provide a superior speed response in terms of rise time and the steady-state error compared to PI and FL controllers.
Abstract: Attempts are being made to enhance the drive performance by intelligent control using fuzzy logic (FL) and neural network techniques. One of the frequently discussed applications of artificial intelligence in control is the replacement of a standard proportional plus integral (PI) speed controller with an FL or artificial neural network (ANN) speed controller. Regardless of all the work, it appears that a thorough comparison of the drive behavior under PI, FL, and ANN speed control is necessary. This article attempts to compare PI, fuzzy, and ANN controllers that are implemented in an embedded system for closed-loop speed control of DC drive fed by a buck-type DC–DC power converter. The PI controller is designed based on the small signal modeling of the system. The PI-like fuzzy controller structure is considered for comparison. Two ANN controllers are designed. One controller uses training data obtained from the simulation of a fuzzy controller and the other uses training data from the simulatio...
TL;DR: In this paper, a fast decoupled power-flow (FDPF) technique based on line current flows in rectangular coordinates for radial distribution systems is presented, which uses a sparse constant sub-Jacobian matrix that needs to be factorized only once for both real and reactive sub-problems.
Abstract: This article presents a fast decoupled power-flow (FDPF) technique based on line current flows in rectangular coordinates for radial distribution systems. The line current flows, computed from the specified load powers and its functions, are rotated by appropriate line admittance angles for zeroing the off-diagonal blocks of the Jacobian and decoupling the power-flow problem into two sub-problems without making any assumptions. The approach is simple and uses a sparse constant sub-Jacobian matrix that needs to be factorized only once for both real and reactive sub-problems and is solved iteratively similar to the FDPF technique. Test results of 15-, 29-, and 69-node systems indicate that the proposed method is efficient, robust, accurate, and has great potential for on-line applications.
TL;DR: In this article, the authors proposed a competitive way to provide frequency regulation ancillary services through price-based and bilateral contracts between Gencos and Discos, and analyzed the dynamic performance of the charged-bilateral structure through a simulation of a step-load disturbance to examine its regulation capabilities for normal operating load and contract violation issues.
Abstract: Part I of this article focuses on the frequency regulation ancillary service and proposes a competitive way to provide this service through price-based and bilateral contracts between Gencos and Discos. The dynamic performance of the charged-bilateral structure is analyzed through a simulation of a step-load disturbance to examine its regulation capabilities for normal operating load and contract violation issues. Part II reports the design of the effective and robust controller for the Part I model and investigates for the integral, dual, and fuzzy controllers with an area control error (ACE)-linked pricing scheme. The simulation results show that fuzzy logic controller performance is better and more robust than the other controllers.
TL;DR: In this article, a power system stabilizer that alleviates generator shaft fatigue through the minimization of the maximum overshoot was proposed, and the levels of control signal, as well as controller parameters, have to be maintained within certain bounds imposed by physical and practical considerations.
Abstract: Power systems are subjected to severe repetitive oscillations that might cause generator shaft fatigue and, consequently, breakdown. In this article, we consider the problem of designing a power system stabilizer that alleviates generator shaft fatigue through the minimization of the maximum overshoot. Moreover, through our design, the levels of control signal, as well as controller parameters, have to be maintained within certain bounds imposed by physical and practical considerations. In this respect, a technique based on the particle swarm approach is proposed to identify the parameters of a fixed structure lead compensator through the solution of a min-max problem while satisfying systems constraints. To enhance the overall performance of the system under wide loading conditions, a set of operating points is considered within our approach. The proposed power system stabilizer is applied to a single-machine infinite-bus system at different loading conditions, and the results showed the effecti...
TL;DR: In this paper, the available transfer capability (ATCTC) of a single-area transmission system is evaluated using power transfer distribution factors in a combined economic emission dispatch environment, and multi-area ATC is calculated with the inclus...
Abstract: Deregulation of the electricity industry throughout the world aims at creating a competitive market to trade electricity, which generates a host of new technical challenges to market participants and power system researchers. For transmission systems, it requires non-discriminatory open access to transmission resources. Therefore, for better transmission services support and full utilization of transmission assets, one of the major challenges is to accurately gauge the transfer capability remaining in the system for further transactions, which is termed the available transfer capability (ATC). It is crucial to develop an appropriate ATC determination methodology that enables one to evaluate the realistic transmission transfer capability by accounting for all related important requirements. This article describes the evaluation of single-area ATC using power transfer distribution factors in a combined economic emission dispatch environment. In addition, multi-area ATC is calculated with the inclus...
TL;DR: In this paper, a technique is developed for the solution of load-frequency control (LFC) problems with state and/or control constraints via the solving of constrained linear quadratic problem (LQP).
Abstract: Load-frequency control (LFC) is one of the major problems when dealing with the design and/or operation of electric power systems. Moreover, due to practical and physical considerations, bounds are often imposed on the level of control signals as well as the maximum frequency deviation. Control strategies that satisfy systems constraints, and, at the same time, guarantee optimal systems performance, are often more difficult to achieve. In this article, a technique is developed for the solution of LFC problems with state and/or control constraints via the solution of constrained linear quadratic problem (LQP). After formulating the problem and deriving the necessary conditions of optimality, an iterative algorithm is proposed that leads to the optimal control strategy while satisfying systems constraints. In order to illustrate the effectiveness of this technique, one- and two-area constrained LFC problems are solved, and the results are demonstrated at the end of the paper.
TL;DR: In this article, a master-slave splitting iterative method is developed for solving the hybrid mixed power-flow problem, and several case studies are carried out, and the accuracy, convergence, efficiency, and reliability of the proposed method are validated.
Abstract: Traditionally, transmission and distribution power flows are studied and developed separately. In order to face keen competition in the market, the coordinated operation between transmission and distribution systems is required. Therefore, in order to balance the boundary mismatch between the transmission and distribution system models existing in the results of traditional power-flow methods, the transmission and distribution systems are studied as a whole in this article. A novel master–slave splitting iterative method is developed for solving the hybrid mixed power-flow problem. Several case studies are carried out, and the accuracy, convergence, efficiency, and reliability of the proposed method are validated.
TL;DR: In this paper, the damping of blade and shaft torsional oscillations of wind turbine generator system (WTGS) when a network disturbance occurs in the power system are analyzed.
Abstract: In this article, the blade and shaft torsional oscillations of wind turbine generator system (WTGS) when a network disturbance occurs in the power system are analyzed. Several reports are available in the literature, where the damping of shaft torsional oscillations of steam turbine generator system is discussed. Though a huge number of wind generators are going to be connected with the existing network, the damping of blade-shaft torsional oscillations of WTGS has so far not been reported. In this work, for the damping of blade-shaft torsional oscillations of WTGS, the voltage source converter (VSC) based three-level STATCOM is proposed. The six-mass drive train model of WTGS is used for the sake of precise analysis. Moreover, the damping of blade-shaft torsional oscillations of WTGS by using pitch controller is analyzed also, since a pitch controller is attached with most of the recent wind turbines. Both symmetrical and unsymmetrical faults are considered as the network disturbances. Simulatio...
TL;DR: In this paper, a direct torque control of doubly-fed induction generators with a space vector modulation scheme for wind energy conversion is presented, where the voltage acting on the rotor winding is directly computed from the differences between reference values and feedback quantities.
Abstract: This article presents a direct torque control of doubly-fed induction generators with a space vector modulation scheme for wind energy conversion. The scheme is to independently control the torque and reactive power flow of the doubly-fed induction generator and directly compute the voltage acting on the rotor winding from the differences between reference values and feedback quantities. As the proposed algorithm is more robust and has less harmonic distortion than the hysteresis direct torque control method, the algorithm will be of great interest to fellow researchers working on doubly-fed induction generators. Computer simulation and experimental results are reported as a validation of the scheme.
TL;DR: In this paper, a comprehensive survey on meter placement for monitoring a power system is provided, where different applications of meter placement, such as transmission, distribution, load, harmonics, and voltage sags, are discussed.
Abstract: The aim of this article is to provide a comprehensive survey on meter placement for monitoring a power system. The different applications of meter placement, such as transmission, distribution, load, harmonics, and voltage sags, are discussed. Algorithms that are used for power system state estimation optimum meter placement are discussed in detail. Comparative graphs are plotted for quantifying the research done in these areas. The authors are of the opinion that the scope of pursuing research in the area of state estimation meter placement is quite state-of-the-art and timely.
TL;DR: In this article, the issue of protection system coordination in reconfigurable distribution systems is dealt with, where the protection coordination requirement restricts the changes in the power flow direction through the distribution lines and drastically reduces the search space to be explored by the network reconfiguration algorithms.
Abstract: The issue of protection system coordination in reconfigurable distribution systems is dealt with in this article. The protection coordination requirement restricts the changes in the power-flow direction through the distribution lines and drastically reduces the search space to be explored by the network reconfiguration algorithms. Moreover, the protection system for the reconfigurable distribution network has to be designed considering all permissible configurations of the network. This article illustrates the protection design procedure through a test network and presents a network reconfiguration algorithm incorporating the protection coordination constraints.