Showing papers on "Electric power system published in 2002"
Book•
31 Aug 2002
TL;DR: Power Quality Enhancement Using Custom Power Devices as discussed by the authors considers the structure, control and performance of series compensating DVR, the shunt DSTATCOM and the SHunt with series UPQC for power quality improvement in electricity distribution.
Abstract: Power Quality Enhancement Using Custom Power Devices considers the structure, control and performance of series compensating DVR, the shunt DSTATCOM and the shunt with series UPQC for power quality improvement in electricity distribution. Also addressed are other power electronic devices for improving power quality in Solid State Transfer Switches and Fault Current Limiters. Applications for these technologies as they relate to compensating busses supplied by a weak line and for distributed generation connections in rural networks, are included. In depth treatment of inverters to achieve voltage support, voltage balancing, harmonic suppression and transient suppression in realistic network environments are also covered. New material on the potential for shunt and series compensation which emphasizes the importance of control design has been introduced. Power Quality Enhancement Using Custom Power Devices is appropriate for distribution engineers, graduate engineers and designers working in the area of power electronic applications for power systems. Sections of the book on power quality issues and generation connection make for a timely reference for undergraduates studying distribution engineering. Written for: Distribution engineers, graduate engineers and designers working in the area of power electronic applications for power systems, students
1,015 citations
TL;DR: In this paper, a model that can be used to represent all types of variable speed wind turbines in power system dynamics simulations is presented, and some results obtained after incorporation of the model in PSS/E, a widely used power system simulation software package, are presented and compared with measurements.
Abstract: A tendency to erect ever more wind turbines can be observed in order to reduce the environmental consequences of electric power generation. As a result of this, in the near future, wind turbines may start to influence the behavior of electric power systems by interacting with conventional generation and loads. Therefore, wind turbine models that can be integrated into power system simulation software are needed. In this contribution, a model that can be used to represent all types of variable speed wind turbines in power system dynamics simulations is presented. First, the modeling approach is commented upon and models of the subsystems of which a variable speed wind turbine consists are discussed. Then, some results obtained after incorporation of the model in PSS/E, a widely used power system dynamics simulation software package, are presented and compared with measurements.
1,001 citations
TL;DR: In this paper, a novel evolutionary algorithm-based approach to optimal design of multimachine power system stabilizers (PSSs) is proposed, which employs the particle swarm optimization (PSO) technique to search for optimal settings of PSS parameters.
Abstract: In this paper, a novel evolutionary algorithm-based approach to optimal design of multimachine power system stabilizers (PSSs) is proposed. The proposed approach employs the particle swarm optimization (PSO) technique to search for optimal settings of PSS parameters. Two elgenvalue-based objective functions to enhance system damping of electromechanical modes are considered. The robustness of the proposed approach to the initial guess is demonstrated. The performance of the proposed PSO-based PSS (PSOPSS) under different disturbances, loading conditions, and system configurations is tested and examined for different multimachine power systems. Eigenvalue analysis and nonlinear simulation results show the effectiveness of the proposed PSOPSSs to damp out the local as well as the interarea modes of oscillations and work effectively over a wide range of loading conditions and system configurations. In addition, the potential and superiority of the proposed approach over the conventional approaches are demonstrated.
684 citations
TL;DR: A number of functional operating constraints, such as branch flow limits, load bus voltage magnitude limits, and generator reactive capabilities, are included as penalties in the GA fitness function (FF).
Abstract: This paper presents an enhanced genetic algorithm (EGA) for the solution of the optimal power flow (OPF) with both continuous and discrete control variables. The continuous control variables modeled are unit active power outputs and generator-bus voltage magnitudes, while the discrete ones are transformer-tap settings and switchable shunt devices. A number of functional operating constraints, such as branch flow limits, load bus voltage magnitude limits, and generator reactive capabilities, are included as penalties in the GA fitness function (FF). Advanced and problem-specific operators are introduced in order to enhance the algorithm's efficiency and accuracy. Numerical results on two test systems are presented and compared with results of other approaches.
620 citations
TL;DR: Cascading failure in a simplified transmission system model as load power demand is increased is examined and it is found that operation near critical points can produce power law tails in the blackout size probability distribution similar to those observed.
Abstract: From the analysis of a 15-year time series of North American electric power transmission system blackouts, we have found that the frequency distribution of the blackout sizes does not decrease exponentially with the size of the blackout, but rather has a power law tail. The existence of a power tail suggests that the North American power system has been operated near a critical point. To see if this is possible, here we explore the critical points of a simple blackout model that incorporates circuit equations and a process through which outages of lines may happen. In spite of the simplifications, this is a complex problem. Understanding the different transition points and the characteristic properties of the distribution function of the blackouts near these points offers a first step in devising a dynamical model for the power transmission systems.
554 citations
10 Dec 2002
TL;DR: In this paper, the feasibility of direct current for the supply of offices and commercial facilities is analyzed by analyzing a case study, i.e., the supply to the Department of Electric Power Engineering, Chalmers University of Technology, Gothenburg, Sweden.
Abstract: This paper analyzes the feasibility of direct current for the supply of offices and commercial facilities. This is done by analyzing a case study, i.e. the supply to the Department of Electric Power Engineering, Chalmers University of Technology, Gothenburg, Sweden. Voltage drop calculations have been carried out for different voltage levels. A backup system for reliable power supply is designed based on commercially available batteries. Finally, an economic evaluation of AC versus DC is performed and protection of the proposed system is briefly addressed.
451 citations
TL;DR: In this paper, a hybrid methodology for solving dynamic economic dispatch (DED) is proposed, in such a way that a simple evolutionary programming (EP) is applied as a based level search, which can give a good direction to the optimal global region, and a local search sequential quadratic programming (SQP) is used as a fine tuning to determine the optimal solution at the final.
Abstract: Dynamic economic dispatch (DED) is one of the main functions of power generation operation and control. It determines the optimal settings of generator units with predicted load demand over a certain period of time. The objective is to operate an electric power system most economically while the system is operating within its security limits. This paper proposes a new hybrid methodology for solving DED. The proposed method is developed,in such a way that a simple evolutionary programming (EP) is applied as a based level search, which can give a good direction to the optimal global region, and a local search sequential quadratic programming (SQP) is used as a fine tuning to determine the optimal solution at the final. A ten-unit test system with nonsmooth fuel cost function is used to illustrate the effectiveness of the proposed method compared with those obtained from EP and SQP alone.
415 citations
TL;DR: Simulation and experimental results show how to operate this converter in order to maintain equal charge/discharge rates from the DC sources (batteries, capacitors, or fuel cells) in an HEV.
Abstract: This paper presents transformerless multilevel converters as an application for high-power hybrid electric vehicle (HEV) motor drives. Multilevel converters: (1) can generate near-sinusoidal voltages with only fundamental frequency switching; (2) have almost no electromagnetic interference or common-mode voltage; and (3) make an HEV more accessible/safer and open wiring possible for most of an HEV's power system. The cascade inverter is a natural fit for large automotive hybrid electric drives because it uses several levels of DC voltage sources, which would be available from batteries, ultracapacitors, or fuel cells. Simulation and experimental results show how to operate this converter in order to maintain equal charge/discharge rates from the DC sources (batteries, capacitors, or fuel cells) in an HEV.
384 citations
TL;DR: In this paper, a one-hour-ahead load forecasting method using the correction of similar day data is proposed, where the forecasted load power is obtained by adding a correction to the selected similar-day data.
Abstract: Load forecasting has always been the essential part of an efficient power system planning and operation. Several electric power companies are now forecasting load power based on conventional methods. However, since the relationship between load power and factors influencing load power is nonlinear, it is difficult to identify its nonlinearity by using conventional methods. Most of papers deal with 24-hour-ahead load forecasting or next day peak load forecasting. These methods forecast the demand power by using forecasted temperature as forecast information. But, when the temperature curves changes rapidly on the forecast day, load power changes greatly and forecast error would going to increase. In conventional methods neural networks uses all similar day's data to learn the trend of similarity. However, learning of all similar day's data is very complex, and it does not suit learning of neural network. Therefore, it is necessary to reduce the neural network structure and learning time. To overcome these problems, we propose a one-hour-ahead load forecasting method using the correction of similar day data. In the proposed prediction method, the forecasted load power is obtained by adding a correction to the selected similar day data.
TL;DR: In this paper, the onset of voltage collapse point is calculated based on the load characteristics and simulated voltage and current phasors measurements, which are provided by a network of phasor-measurement units.
Abstract: This paper presents a concept for local monitoring of the onset of voltage collapse, protective, and emergency control in the presence of voltage-sensitive loads. The onset of voltage collapse point is calculated based on the load characteristics and simulated voltage and current phasors measurements, which are provided by a network of phasor-measurement units. If the stability margin is small and the reactive-power reserves are nearly exhausted, then controls to steer the power system away from the critical point will be activated.
07 Nov 2002
TL;DR: In this article, the authors provide a tutorial introduction to phasor measurement units (PMU) when applied in a power system environment, provide an overview of communication alternatives for wide area measurement systems (WAMS), and compute the delay budget for each type of communication link.
Abstract: This paper provides a tutorial introduction to phasor measurement units (PMU) when applied in a power system environment, provides an overview of communication alternatives for wide area measurement systems (WAMS), and computes the delay budget for each type of communication link. The goal of this study is to provide data regarding the communication delay that can be incorporated into the analysis and simulation of WAMS.
TL;DR: In this paper, commercial supercapacitors from Saft, Maxwell, Panasonic, CCR, Ness, EPCOS, and Power Systems were tested under constant current and constant power discharges to assess their applicability for power-assist applications in hybrid electric vehicles (HEVs).
TL;DR: In this article, an agreement was concluded with Geological Survey of Canada (GSC) for sending a warning alert to the Network Control Centre (CCR) before any anticipated severe geomagnetic storms.
TL;DR: In this paper, the modeling of wind turbines for power system studies is investigated, and the results are verified by field measurements made on a stall-regulated fixed-speed wind turbine.
Abstract: In this paper, the modeling of wind turbines for power system studies is investigated. Complexities of various parts of a wind turbine model, such as aerodynamic conversion, drive train, and generator representation, are analyzed. The results are verified by field measurements made on a stall-regulated fixed-speed wind turbine. The modeling focuses on deriving a representation that is suitable for use in grid simulation programs.
08 May 2002
TL;DR: In this article, the authors investigated the opportunities and challenges associated with adopting a dc distribution scheme for indus- trial power systems and proposed a grounding scheme and showed that this scheme provides an ef- fective solution by keeping the neutral voltages low under normal conditions and by limiting the fault currents during fault condi- tions.
Abstract: This paper investigates the opportunities and chal- lenges associated with adopting a dc distribution scheme for indus- trial power systems. A prototype dc distribution system has been simulated to investigate the issues. One of the issues focused is the interaction between power converters that are used to convert ac to dc and dc to ac. Another challenging issue investigated is the system grounding. These issues become challenging mainly due to the neu- tral voltage shift associated with the power converters. The paper shows that converter interactions can be minimized with proper filtering and control on the converters. The paper also proposes a grounding scheme and shows that this scheme provides an ef- fective solution by keeping the neutral voltages low under normal conditions and by limiting the fault currents during fault condi- tions. With these features, dc distribution provides very reliable and high-quality power.
TL;DR: In this article, two simple, simple solidoxide fuel-cell (SOFC) power systems fed by hydrogen and methane, respectively, are examined and the energy and exergy at each node of the system are conducted and their respective values are normalized by the lower heating value of the fuel and its chemical exergy, respectively.
07 Nov 2002
TL;DR: In this article, the authors show that a "converter-per-module" approach offers many advantages including individual module maximum power point tracking, which gives great flexibility in module layout, replacement, and insensitivity to shading; better protection of PV sources, and redundancy in the case of source or converter failure.
Abstract: New residential scale photovoltaic (PV) arrays are commonly connected to the grid by a single DC-AC inverter connected to a series string of PV modules, or many small DC-AC inverters which connect one or two modules directly to the AC grid. This paper shows that a "converter-per-module" approach offers many advantages including individual module maximum power point tracking, which gives great flexibility in module layout, replacement, and insensitivity to shading; better protection of PV sources, and redundancy in the case of source or converter failure; easier and safer installation and maintenance; and better data gathering. Simple nonisolated per-module DC-DC converters can be series connected to create a high voltage string connected to a simplified DC-AC inverter. These advantages are available without the cost or efficiency penalties of individual DC-AC grid connected inverters. Buck, boost, buck-boost and Cuk converters are possible cascadable converters. The boost converter is best if a significant step up is required, such as with a short string of 12 PV modules. A string of buck converters requires many more modules, but can always deliver any combination of module power. The buck converter is the most efficient topology for a given cost. While flexible in voltage ranges, buck-boost and Cuk converters are always at an efficiency or alternatively cost disadvantage.
07 Aug 2002
TL;DR: In this article, the authors present a control technique for distributed generation (DG) plants that use feedback of only locally measurable variables, which allows correct system operation and switching between parallel and isolated modes without needing online communication of control signals between the generators.
Abstract: It is expected that dispersed generation (DG) will play an increasing role in electric power systems in the near future. Among the benefits that DG can give to the power system operators and to the electricity customers, one of the most attractive is the possibility of improving the continuity of power supply. DG plants can be designed to supply portions of the distribution grid in the event of an upstream supply outage. Techniques for controlling DG plants that use feedback of only locally measurable variables are presented. This solution allows correct system operation and switching between parallel and isolated modes without needing online communication of control signals between the generators. The control technique is described with particular reference to inverter-interfaced systems (micro-turbines, fuel cells). Simulations of sample cases including different size and type of generators are presented.
25 Jul 2002
TL;DR: In this paper, the impact of distributed generation technology and penetration level on the dynamics of a test system is investigated, and it is found that the effects of distributed generators on the dynamic behavior of a power system strongly depend on the technology of the distributed generators.
Abstract: It is expected that increasing amounts of new generation technologies will be connected to electrical power systems in the near future. Most of these technologies are of considerably smaller scale than conventional synchronous generators and are therefore connected to distribution grids. Further, many are based on technologies different from the synchronous generator, such as the squirrel cage induction generator and high or low speed generators that are grid coupled through a power electronic converter. When connected in small amounts, the impact of distributed generation on power system transient stability will be negligible. However, if its penetration level becomes higher, distributed generation may start to influence the dynamic behavior of the power system as a whole. In this paper, the impact of distributed generation technology and penetration level on the dynamics of a test system is investigated. It is found that the effects of distributed generation on the dynamics of a power system strongly depend on the technology of the distributed generators.
TL;DR: In this paper, the authors proposed a self-healing strategy to deal with catastrophic events when power system vulnerability analysis indicates that the system is approaching an extreme emergency state, and a load shedding scheme based on the rate of frequency decline is applied.
Abstract: This paper provides a self-healing strategy to deal with catastrophic events when power system vulnerability analysis indicates that the system is approaching an extreme emergency state. In the authors' approach, the system is adaptively divided into smaller islands with consideration of quick restoration. Then, a load shedding scheme based on the rate of frequency decline is applied. The proposed scheme is tested on a 179-bus, 20-generator sample system and shows very good performance.
07 Nov 2002
TL;DR: In this article, a fast voltage stability index (FVSI) was proposed to determine the maximum capacity limit before voltage collapse so that necessary precaution can be taken to avoid system capacity violation.
Abstract: Since a couple of decades ago, voltage stability assessment has received increasing attention due to the complexity of power systems. With the increase in power demand and limited power sources has caused the system to operate at its maximum capacity. Therefore, a study that is able to determine the maximum capacity limit before voltage collapse must be carried out so that necessary precaution can be taken to avoid system capacity violation. This paper presents a novel fast voltage stability index (FVSI) simplified from a pre-developed voltage stability index referred to a line initiated from the voltage quadratic equation at the sending end of a representation of a 2-bus system. The line index in the interconnected system in which the value that is closed to 1.00 indicates that the line has reached its instability limit which could cause sudden voltage drop to the corresponding bus caused by the reactive load variation. The formulated index was tested on the IEEE reliability test system in order to verify the performance of the proposed indicator. Results showed that the proposed technique is indicative in predicting the occurrence of system collapse and hence necessary action can be taken to avoid such incident.
Patent•
19 Mar 2002
TL;DR: In this article, a power distribution rack, and uninterruptible power supply rack and a plurality of equipment racks are installed in a building and a power cable is run from the distribution rack to each of the equipment racks using power cable tracks.
Abstract: Systems and method for installing computer equipment and power distribution equipment in facilities is provided. In one aspect, the present invention provides a power distribution rack, and uninterruptible power supply rack and a plurality of equipment racks. A plurality of power cables are run from the power distribution rack to each of the plurality of equipment racks using power cable tracks located on the roofs of the equipment racks.
TL;DR: The p-q-r theory as discussed by the authors provides two degrees of freedom to control the system currents by only compensating the instantaneous imaginary power without using any energy storage element, and the definition of powers maintains power conservation, and agrees well with the general understanding of power.
Abstract: This paper proposes a novel power compensation algorithm in three-phase four-wire systems by using p-q-r theory. The p-q-r theory is compared with two previous instantaneous power theories, p-q theory and cross vector theory. The p-q-r theory provides two-degrees of freedom to control the system currents by only compensating the instantaneous imaginary power without using any energy storage element. The definition of powers maintains power conservation, and agrees well with the general understanding of power. Simulation results show the superiority of p-q-r theory both in definition and compensation.
TL;DR: An expert system is presented that is able to classify different types of power system events to the underlying causes and offer useful information in terms of power quality and enables fast and accurate analysis of data from power quality monitors.
Abstract: This paper presents an expert system that is able to classify different types of power system events to the underlying causes (i.e., events) and offer useful information in terms of power quality. The expert system uses the voltage waveforms and distinguishes the different types of voltage dips (fault-induced, transformer saturation, induction motor starting), as well as interruptions (nonfault, fault induced). A method for event-based classification is used, where a segmentation algorithm is first applied to divide waveforms into several possible events. The expert system is tested using real measurements and the results show that the system enables fast and accurate analysis of data from power quality monitors.
TL;DR: In this paper, a supervisory level power system stabilizer (SPSS) using wide area measurements is proposed, which is capable of compensating for the nonlinear dynamic operation of power systems and uncertain disturbances.
Abstract: Conventional power system stabilizers (PSSs) are major local damping controllers acting through generator excitation systems. There are studies that suggest that remote signals could increase damping beyond that attainable by local signals. In this paper, a supervisory level power system stabilizer (SPSS) using wide area measurements is proposed. The robustness of the proposed controller is capable of compensating for the nonlinear dynamic operation of power systems and uncertain disturbances. The coordination of the robust SPSSs and local PSSs is implemented based on the principles of multiagent system theory. This theory is an active branch of applications in distributed artificial intelligence (DAI). The performance of the robust controller as a power system stability agent is studied using a 29-machine 179-bus power system example.
TL;DR: A novel DC-AC converter for applications in the area of distributed energy generation systems, e.g., solar power systems, fuel-cell power systems in combination with supercapacitor or battery energy storage, using an isolated multicell topology is presented.
Abstract: This paper presents a novel DC-AC converter for applications in the area of distributed energy generation systems, e.g., solar power systems, fuel-cell power systems in combination with supercapacitor or battery energy storage. The proposed converter is realized using an isolated multicell topology where the total AC output of the system is formed by series connection of several full-bridge converter stages. The DC links of the full bridges are supplied by individual DC-DC isolation stages which are arranged in parallel concerning the dc input of the. total system. Therefore, all switching cells of the proposed converter can be equipped with modern low-voltage high-current power MOSFETs, which results in an improved efficiency as compared to conventional isolated DC-AC converters. Furthermore, the cells are operated in an interleaved pulsewidth-modulation mode which, in connection with the low voltage level of each cell, significantly reduces the filtering effort on the AC output of the overall system. The paper describes the operating principle, analyzes the fundamental relationships which are relevant for component selection, and presents a specific circuit design. Finally, measurements taken from a 2-kW laboratory model are presented.