Showing papers on "Electric power system published in 2001"

Optimal Location of Multi-Type FACTS Devices in a Power System by Means of Genetic Algorithms

Abstract: This paper presents a genetic algorithm to seek the optimal location of multi-type FACTS devices in a power system. The optimizations are performed on three parameters: the location of the devices, their types, and their values. The system loadability is applied as a measure of power system performance. Four different kinds of FACTS controllers are used and modeled for steady-state studies: TCSC, TCPST, TCVR, and SVC. Simulations are done on a 118-bus power system for several numbers of devices. Results show the difference of efficiency of the devices used in this context. They also show that the simultaneous use of several kinds of controllers is the most efficient solution to increase the loadability of the system. In all the cases (single-and multi-type FACTS devices), we observe a maximum number of devices beyond which this loadability cannot be improved.

Wide-area measurement based stabilizing control of large power systems-a decentralized/hierarchical approach

Abstract: The aim of this paper is to assess the capability of the emerging synchronized phasor measurement technology in improving the overall stability of the Hydro-Quebec transmission system through supplementary modulation of voltage regulators. Following a thorough singular value and eigenvalue analysis of the system dynamic interactions, five control sites consisting of four generators and one synchronous condenser are chosen to implement new power system stabilizers with a supplementary input from remote phasor measuring units, geographically spread over nine electrically coherent areas. Since the remote feedback loops are built on top of an existing decentralized control system, this design approach results in a decentralized/hierarchical control architecture with significant advantages in terms of reliability and operational flexibility. A systematic control and measurement pairing yielded four dominant natural loops, each associated with a significant open-loop inter-area oscillatory mode at 0.06, 0.4, 0.7 and 0.95 Hz respectively. These PSSs have a speed sensitive local loop operating in the usual way, and a wide-area measurement based global loop which involves a single differential frequency signal between two suitably selected areas. The tuning and coordination technique for these advanced multiple input signals PSSs is described. Their impacts on the system is assessed using both small-signal analysis and nonlinear simulations in a transient stability program. Wide-area stabilizing controllers have a significant potential in improving the dynamic performance of the Hydro-Quebec's existing power system.

Short-term hourly load forecasting using time-series modeling with peak load estimation capability

Abstract: This paper presents a new time series modeling for short term load forecasting, which can model the valuable experiences of the expert operators. This approach can accurately forecast the hourly loads of weekdays, as well as, of weekends and public holidays. It is shown that the proposed method can provide more accurate results than the conventional techniques, such as artificial neural networks or Box-Jenkins models. In addition to hourly loads, daily peak load is an important problem for dispatching centers of a power network. Most of the common load forecasting approaches do not consider this problem. It is shown that the proposed method can exactly forecast the daily peak load of a power system. Obtained results from extensive testing on the Iran's power system network confirm the validity of the developed approach.

Dynamic modelling of a wind turbine with doubly fed induction generator

Abstract: As a result of increasing environmental concern, more and more electricity is generated from renewable sources. One way of generating electricity from renewable sources is to use wind turbines. A tendency to erect more and more wind turbines can be observed. As a result of this, in the near future wind turbines may start to influence the behaviour of electrical power systems. Therefore, adequate models to study the impact of wind turbines on electrical power system behaviour are needed. In this paper, a dynamic model of an important contemporary wind turbine concept is presented, namely a doubly fed (wound rotor) induction generator with a voltage source converter feeding the rotor. This wind turbine concept is equipped with rotor speed, pitch angle and terminal voltage controllers. After derivation of the model, the wind turbine response to two measured wind sequences is simulated.

Application of tabu search to optimal placement of distributed generators

Abstract: Distributed generators (DGs) such as fuel cells, solar cells, wind mills and micro gas turbines, etc. are going to be installed on the demand side of power systems. Such distributed generators can reduce distribution loss if they are placed appropriately in the distribution system. In this paper, a tabu search application for finding the optimal allocation of DGs from a viewpoint of loss minimization is illustrated. In other words, the authors discuss about an implementation method of tabu search to find how much distribution loss can be reduced if DGs are optimally allocated at the demand side of a power system. Namely, locations and discrete capacities of DGs to minimize the distribution loss are determined by nested use of the tabu search algorithm. Numerical examples are shown to demonstrate the method.

Modeling and Analysis of Custom Power Systems by PSCAD/EMTDC

Abstract: This paper addresses the timely issue of modeling and analysis of custom power controllers, a new generation of power electronics-based equipment aimed at enhancing the reliability and quality of power flows in low-voltage, distribution networks [2],[3] The modeling approach adopted in this article is graphical in nature, as opposed to mathematical models embedded in code using a high-level computer language The well-developed graphic facilities available in an industry standard power system package, namely, PSCAD/EMTDC, are used to conduct all aspects of model implementation and to carry out extensive simulation studies Graphics-based models suitable for electromagnetic transient studies are presented for the following three custom power controllers: the distribution static compensator (D-STATCOM), the dynamic voltage restorer (DVR), and the solid-state transfer switch (SSTS) Comprehensive results are presented to assess the performance of each device as a potential custom power solution The paper is written in a tutorial style and aimed at the large PSCAD/EMTDC user base

An initial model fo complex dynamics in electric power system blackouts

Abstract: We define a model for the evolution of a long series of electric power transmission system blackouts. The model describes opposing forces, which have been conjectured to cause self-organized criticality in power system blackouts. There is a slow time scale representing the opposing forces of load growth and growth in system capacity and a fast time scale representing cascading line overloads and outages. The time scales are coupled: load growth leads to outages and outages lead to increased system capacity. The opposing forces result in a dynamic equilibrium in which blackouts of all sizes occur. The model is a means to study the complex dynamics of this dynamic equilibrium. The Markov property of the model is briefly discussed. The model dynamic equilibrium is illustrated using initial results from the 73-bus IEEE reliability test system.

Steady-State Performance of a Grid-Connected Rooftop Hybrid Wind-Photovoltaic Power System with Battery Storage

Abstract: This paper reports the performance of a 4 kW grid-connected residential wind-photovoltaic system (WPS) with battery storage located In Lowell, MA. The system was originally designed to meet a typical New England (TNE) load demand with a loss of power supply probability (LPSP) of one day in ten years, as recommended by the Utility Company. The data used in the calculation were wind speed and irradiance of Logan Airport Boston (LAB), obtained from the National Climate Center in North Carolina. The present performance study is based on two-year operation (May 1996 to April 1998) of the WPS. Unlike conventional generation, the wind and the sunrays are available at no cost and generate pollution-free electricity. At around noon the WPS satisfies its load and provides additional energy to the storage or to the grid. On-site energy production is undoubtedly accompanied with minimization of environmental pollution, reduction of losses in power systems transmission and distribution equipment, and supports the utility in demand side management (DSM). This paper includes discussions on system reliability, power quality, loss of supply, and effects of the randomness of the wind and the solar radiation on system design.

Understanding Power System Hannonics

Abstract: Harmonics – Past to Present Power systems are designed to operate at frequencies of 50 or 60Hz. However, certain types of loads produce currents and voltages with frequencies that are integer multiples of the 50 or 60 Hz fundamental frequency. These higher frequencies are a form of electrical pollution known as power system harmonics. Power system harmonics are not a new phenomenon. Concern over harmonic distortion has ebbed and flowed during the history of electric power systems. Steinmetz published a book in 1916 that devoted considerable attention to the study of harmonics in three-phase power systems. His main concern was third harmonic currents caused by saturated iron in transformers and machines, and he was the first to propose delta connections for blocking third harmonic currents. Later, with the advent of rural electrification and telephone service, power and telephone circuits were often placed on common rights-of-way. Harmonic currents produced by transformer magnetizing currents caused inductive interference with open-wire telephone systems. The interference was so severe at times that voice communication was impossible. This problem was studied and alleviated by filtering and by placing design limits on transformer magnetizing currents. Today, the most common sources of harmonics are power electronic loads such as adjustable-speed drives (ASDs) and switch-mode power supplies. These loads use diodes, silicon-controlled rectifiers (SCRs), power transistors, and other electronic switches to chop waveforms to control power or to convert 50/60Hz AC to DC. In the case of ASDs, the DC is then converted to variable-frequency AC to control motor speed. Example uses of ASDs include chillers and pumps. Due to tremendous advantages in efficiency and controllability, power electronic loads are proliferating and can be found at all power levels – from low voltage appliances to high voltage converters. Hence, power systems harmonics are once again an important problem.

Dc to dc converter and power management system

Abstract: A DC to DC Converter includes an electrical circuit that allows batteries and other electrical energy storage devices to be charged from or to discharge to a variable voltage DC bus. This electrical circuit also enables seamless integration with other energy storage devices and/or DC power sources, such as fuel cells, to provide DC power for a Power Management System. A Power Management System preferably provides both full power source management and power conditioning. The Power Management System is able to manage power flow to and from multiple, isolated power sources and energy storage devices to deliver high quality alternating current (“AC”) power to a load.

Operation of restructured power systems

Abstract: List of Acronyms. Preface. 1. Deregulation of the Electricity Supply Industry. 2. Power System Economic Operation Overview. 3. Power System Operation in Competitive Environment. 4. Transmission Open Access and Pricing Issues. 5. Ancillary Services Management. 6. Reliability and Deregulation. 7. Power Quality Issues: Voltage Dips and Other Disturbances. Index.

Global electric power reform, privatization and liberalization of the electric power industry in developing countries

Abstract: In many developing countries, and in particular those in Asia, the Middle East, and Africa, reform of the power sector starts from a market structure that is dominated by a state-owned national power utility with a legally endowed monopoly and a vertically integrated supply chain encompassing power generation, transmission, distribution, and customer services. The rationale for this structure is minimization of the costs of coordination between these functions and of financing the development of power systems. The pre-reform structure in other countries, notably in South America, places distribution and customer services with local companies, separate from national companies that provide power generation and transmission. Power reforms are designed to introduce competition where feasible, which is in the upstream production and downstream supply functions of the industry structure, and to use economic regulation of the wholesale and retail power markets to promote competition and protect consumer interests. Regulation of the power market is essential, as shown by the experience of New Zealand, which tried an approach without the amount of regulation used elsewhere. Their approach was based on mandatory separation of generation, transmission, and distribution, using general competition laws to deal with both the terms of interconnection and conduct generally in unbundled power networks.

Power Electronic Control in Electrical Systems

Abstract: Preface Electrical power systems - an overview Power systems engineering - fundamental concepts Transmission system compensation Power flows in compensation and control studies Power semiconductor devices and converter hardware issues Power electronic equipment Harmonic studies of power compensating plant Transient studies of FACTS and Custom Power equipment Examples, problems and exercises Appendix Bibliography Index

Optimal distributed generation allocation in MV distribution networks

Abstract: The necessity for flexible electric systems, changing regulatory and economic scenarios, energy savings and environmental impact are providing impetus to the development of distributed generation (DG), which is predicted to play an increasing role in the electric power system of the future. With so much new distributed generation being installed, it is critical that the power system impacts be assessed accurately so that DG can be applied in a manner that avoids causing degradation of power quality, reliability and control of the utility system. For these reasons, the paper proposes a new software procedure, based on a genetic algorithm, capable of establishing the optimal distributed generation allocation on an existing MV distribution network, considering all the technical constraints, like feeder capacity limits, feeder voltage profile and three-phase short circuit current in the network nodes.

Reliability/Cost Implications of PV and Wind Energy Utilization in Small Isolated Power Systems

Abstract: The application of renewable energy in electric power systems is growing rapidly due to enhanced public concerns for adverse environmental impacts and escalation in energy costs associated with the use of conventional energy sources. Photovoltaics and wind energy sources are being increasingly recognized as cost-effective generation sources in small isolated power systems primarily supplied by costly diesel fuel. The utilization of these energy sources can significantly reduce the system fuel costs but can also have considerable impact on the system reliability. A realistic cost/reliability analysis requires evaluation models that can recognize the highly erratic nature of these energy sources while maintaining the chronology and interdependence of the random variables inherent in them. This paper presents a simulation method that provides objective indicators to help system planners decide on appropriate installation sites, operating policies, and selection of energy types, sizes, and mixes in capacity expansion when utilizing PV and wind energy in small isolated systems.

Nonlinear control systems and power system dynamics

Abstract: Preface. 1. Introduction. 2. Basic Concepts of Nonlinear Control Theory. 3. Design Principles of Single-Input Single-Output Nonlinear Control Systems. 4. Design Principles of Multi-Input Multi-Output Nonlinear Control Systems. 5. Basic Mathematical Descriptions for Electric Power Systems. 6. Nonlinear Excitation Control of Large Synchronous Generators. 7. Nonlinear Steam Valving Control. 8. Nonlinear Control of HVDC Systems. 9. Nonlinear Control of Static Var Systems. 10. Nonlinear Robust Control of Power Systems. Index.

Power Systems Harmonics: Fundamentals, Analysis and Filter Design

Abstract: Contents: Introduction - Fundamentals of Harmonics - Causes of Harmonics in Power Systems - Effects of Harmonic Distortion on Power Systems - Mitigation of Power System Harmonics - Limits of Harmonic Distortion - Modelling of System Components for Harmonic Studies -Transformer Modelling - Modelling of Transmission Lines / Cables - A Simple Approach to Power System Harmonic Studies - Bibliography - Appendix A: A Review of Transformation and Symmetrical Components - Appendix B: Phase and Sequence Admittance Matrices for Three-Phase Transformers - Appendix C: Transmission Matrices for Three-Phase Transformers - Index.

System, method, rotating machine and computer program product for enhancing electric power produced by renewable facilities

Abstract: An electric power system provides a coordinated and controlled intercommunication and operation of power engineering equipment and converters, e.g., rotating AC machines, power electronic converters and transformers as well as power grids in order to enhance electric power produced by renewable facilities. As viewed from the power grid and its stakeholders' perspective, enhanced renewable facilities are more stiff than conventional renewable facilities, and produce power that is as commercially valuable and fungible as electric power produced by traditional plants such as fossil fuel power plants, hydroelectric plants, nuclear plants and the like. xMs and SMs, or more generally yMs, fulfill the demands of stiffness and reduced variability, which have conventionally limited the commercial usefulness of a large scale use of renewables delivering power to a power grid.

Modeling, control, and design of input-series-output-parallel-connected converter for high-speed-train power system

Abstract: In this paper, a charge control with an input voltage feedforward is proposed for an input-series-output-parallel-connected converter configuration for the high-speed-train power system application. This control scheme accomplishes the output current sharing. For the output-parallel-connected modules as well as the input voltage sharing for the input-series-connected modules for all operating conditions including the transients. It also offers the robustness for the input voltage sharing control according to the component value mismatches among the modules. This configuration enables the usage of a MOSFET for a high-voltage system allowing a higher switching frequency for a lighter system weight and smaller size. The performance of the proposed scheme is verified through the experimental results.

Power System Security Assessment Using Neural Networks: Feature Selection Using Fisher Discrimination

Abstract: One of the most important considerations in applying neural networks to power system security assessment is the proper selection of training features. Modem interconnected power systems often consist of thousands of pieces of equipment, each of which may have an affect on the security of the system. Neural networks have shown great promise for their ability to quickly and accurately predict the system security when trained with data collected from a small subset of system variables. This paper investigates the use of Fisher's linear discriminant function, coupled with feature selection techniques as a means for selecting neural network training features for power system security assessment. A case study is performed on the IEEE 50-generator system to illustrate the effectiveness of the proposed techniques.

Control Lyapunov Functions for Controllable Series Devices

Abstract: Summary form only given as follows. Controllable series devices (CSD), i.e. series-connected flexible AC transmission systems (FACTS) devices, such as unified power controller (UPFC), controllable series capacitor (CSC) and quadrature boosting transformer (QBT) with a suitable control scheme can improve transient stability and help to damp, electromechanical oscillations. For these devices, a general model, which is referred to as the injection model, is used. This model is valid for load flow and angle stability analysis and is helpful for understanding the impact of the CSD on power system stability. Also, based on Lyapunov theory a control strategy for damping of electromechanical power oscillations in a multi-machine power system is derived. Lyapunov theory deals with dynamic systems without inputs. For this reason, it has traditionally been applied only to closed-loop control systems, that is, systems for which the input has been eliminated through the substitution of a predetermined feedback control. However, in this paper, we use Lyapunov function candidates in feedback design itself by making the Lyapunov derivative negative when choosing the control. This control strategy is called control Lyapunov function (CLF) for systems with control inputs.

Capacitive components for power electronics

Abstract: As the consumer and industrial requirements for compact, high-power density electrical power systems grow substantially over the next decade, development of high power/energy density capacitor technology is a major enabling technology component element. For microsecond to fractional-second electrical energy storage, discharge, filtering, and power conditioning, capacitor technology is unequalled in flexibility and adaptability to meet a broad range of requirements in the future.

Optimal operation solutions of power systems with transient stability constraints

Abstract: The computation of an optimal operation point in power systems is a nonlinear optimization problem in functional space, which is not easy to deal with precisely, even for small-scale power systems. On the other hand, the emergence of competitive power markets makes optimal power flow (OPF) with transient stability constraints increasingly important because the conventionally heuristic evaluation for the operation point can produce a discrimination among market players in the deregulated power systems. Instead of directly tackling this tricky problem, in this paper, OPF with transient stability constraints (OTS) is equivalently converted into an optimization problem in the Euclidean space via a constraint transcription, which can be viewed as an initial value problem for all disturbances and solved by any standard nonlinear programming techniques adopted by OPF. The transformed OTS problem has the same variables as those of OPF in form, and is tractable even for the large-scale power systems with a large number of transient stability constraints. This paper also derives the Jacobian matrices of the transient stability constraints and gives two computation algorithms based on the relaxation scheme. The numerical simulation verified the effectiveness of the proposed approach.

Global Transient Stability and Voltage Regulation for Power Systems

Abstract: Summary form only given as follows. This paper is concerned with the global control of power systems. It arises from the practical concern that transient stability and voltage regulation are both important properties of power system control, but they are ascribed to different model descriptions and relate to different stages of system operation (i.e. transient period and post-transient period respectively). Earlier control results deal with the two problems separately, or employ a switching strategy of two different kinds of controllers, which causes a discontinuity of system behavior. We design in this paper a global controller to co-ordinate the transient stabilizer and voltage regulator. The designed controller is smooth and robust with respect to different transient faults. Simulations on a single-machine infinite bus power system have demonstrated better performances compared with existing controllers.

Optimization and Coordination of Damping Controls for Improving System Dynamic Performance

Abstract: This paper presents a global tuning procedure for FACTS device stabilizers (FDS) and power system stabilizers (PSS) in a multi-machine power system using a parameter-constrained nonlinear optimization algorithm implemented in a simulation program. This algorithm deals with such an optimization problem by solving a sequential quadratic programming using the dual algorithm. The main objective of this procedure is to simultaneously optimize pre-selected parameters of the FDSs and PSSs having fixed parameters in coping with the complex nonlinear nature of the power system. By minimizing a nonexplicit target function in which the oscillatory rotor modes of the generators involved and suing characteristics between areas are included, interactions among the FACTS controls under transient conditions in a multimachine power system are improved. A multimachine power system equipped with a TCSC and an SVC as well as three PSSs is applied to demonstrate the efficiency and robustness of the tuning procedure presented. The results obtained from simulations validate the improvement in damping of overall power oscillations in the system in an optimal and globally coordinated manner. The simulations also show that the stabilizers tuned are robust in providing adequate damping for a range of conditions in the system.

Transients in Power Systems

Abstract: Covering the fundamentals of electrical transients, this book should equip readers with the skills to recognise and solve transient problems in power networks and components. Starting with the basics of transient electrical circuit theory, and moving on to discuss the effects of power transience in all types of power equipment, it provides insight into this important field. Recent advances in measurement techniques, computer modelling and switchgear development are given comprehensive coverage for the first time. An electromagnetic transients calculation program is included and should prove valuable to both students and engineers in the field.

Solution for the crisis in electric power supply

Abstract: New techniques for grid monitoring, protection, and control have been perfected, and their judicious application can help reduce the frequency and severity of catastrophic failures. This article describes the development of an innovative multiagent approach to prevent and control catastrophic failures in large power systems. The research has created understanding of the origin and nature of catastrophic failures. This is achieved by an analysis of hidden failures in protection systems. Vulnerabilities associated with the power system, the information network, and the communication network are also evaluated. The approach is characterized by the extensive use of real-time information from diverse sources, coupled with the development of an evolving dynamic decision event tree. A novel multiagent based platform is used to evaluate system vulnerability to catastrophic events taking in account the market environment and competing entities. Several new concepts associated with wide-area measurements and controls, networked sensors, and adaptive self healing are used to reconfigure the network to minimize the system vulnerability. Approaches developed in this research will provide important solutions for power systems and other interconnected networks of the future.

Impact of renewable distributed generation on power systems

Abstract: The traditional approach in electric power generation is to have centralized plants distributing electricity through an extensive transmission & distribution network. Distributed generation (DG) provides electric power at a site closer to the customer, eliminating the unnecessary transmission and distribution costs. In addition, it can reduce fossil fuel emissions, defer capital cost, reduce maintenance investments and improve the distribution feeder voltage conditions. In the case of small residential photovoltaic (PV) and wind systems, the actual generator locations and DG penetration level are usually not apriori known. The following study attempts to calculate the boundaries of the impact of randomly placed distributed generators on a distribution feeder. Monte Carlo simulations are performed, and boundaries for overall improvements are determined. The study shows that the knowledge of total penetration of small PV systems is sufficient to estimate the effects of DG on the feeder.