Showing papers on "Power-flow study published in 2007"

Point Estimate Schemes to Solve the Probabilistic Power Flow

Abstract: This paper analyzes the behavior of Hong's point estimate methods to account for uncertainties on the probabilistic power flow problem. This uncertainty may arise from different sources as load demand or generation unit outages. Point estimate methods constitute a remarkable tool to handle stochastic power system problems because good results can be achieved by using the same routines as those corresponding to deterministic problems, while keeping low the computational burden. In previous works related to power systems, only the two-point estimate method has been considered. In this paper, four different Hong's point estimate schemes are presented and tested on the probabilistic power flow problem. Binomial and normal distributions are used to model input random variables. Results for two different case studies, based on the IEEE 14-bus and IEEE 118-bus test systems, respectively, are presented and compared against those obtained from the Monte Carlo simulation. Particularly, this paper shows that the use of the scheme provides the best performance when a high number of random variables, both continuous and discrete, are considered.

Particle Swarm Optimization Based Capacitor Placement on Radial Distribution Systems

Abstract: This paper presents a novel approach that determines the optimal location and size of capacitors on radial distribution systems to improve voltage profile and reduce the active power loss. Capacitor placement & sizing are done by loss sensitivity factors and particle swarm optimization respectively. The concept of loss sensitivity factors and can be considered as the new contribution in the area of distribution systems. Loss sensitivity factors offer the important information about the sequence of potential nodes for capacitor placement. These factors are determined using single base case load flow study. particle swarm optimization is well applied and found to be very effective in radial distribution systems. The proposed method is tested on 10,15, 34, 69 and 85 bus distribution systems.

An Improved Backward/Forward Sweep Load Flow Algorithm for Radial Distribution Systems

Abstract: This letter presents an improved backward/ forward sweep algorithm for three-phase load-flow analysis of radial distribution systems. In the backward sweep, Kirchhoff's Current Law and Kirchhoff's Voltage Law are used to calculate the upstream bus voltage of each line or a transformer branch. Then, the linear proportional principle is adopted to find the ratios of the real and imaginary components of the specified voltage to those of the calculated voltage at the substation bus. In the forward sweep, the voltage at each downstream bus is then updated by the real and imaginary components of the calculated bus voltage multiplying with the corresponding ratio. The procedure stops after the mismatch of the calculated and the specified voltages at the substation is less than a convergence tolerance. The proposed algorithm is tested with three IEEE benchmark distribution systems. Results show that the algorithm is accurate and computationally efficient in comparing with two other commonly used methods

Development of Three-Phase Unbalanced Power Flow Using PV and PQ Models for Distributed Generation and Study of the Impact of DG Models

Abstract: With the increased installations of distributed generators (DGs) within power systems, load flow analysis of distribution systems needs special models and algorithms to handle multiple sources. In this paper, the development of an unbalanced three-phase load flow algorithm that can handle multiple sources is described. This software is capable of switching the DG mode of operation from constant voltage to constant power factor. The algorithm to achieve this in the presence of multiple DGs is proposed. Shipboard power systems (SPS) have other special characteristics apart from multiple sources, which make the load flow difficult to converge. The developed software is verified for a distribution system without DG using the Radial Distribution Analysis Package (RDAP). The developed software analyzes an IEEE test case and an icebreaker ship system. System studies for the IEEE 37-node feeder without the regulator show the effect of different models and varying DG penetration related to the increase in loading. System losses and voltage deviations are compared.

Optimized Restoration of Unbalanced Distribution Systems

Abstract: A novel formulation for service restoration algorithm for unbalanced three phase distribution systems is described. This problem is a constrained multiobjective optimization formulated as a mixed integer non-linear programming problem. A comparison of the solutions with and without switch pairs has been made. The formulation was first validated using already developed three-phase unbalanced power flow software. The three-phase unbalanced power flow equations were embedded in the formulation, and hence separate calculations were not needed. Simulation results are presented for modified IEEE 13-node and IEEE 37-node test cases

Steady-State Model and Power Flow Analysis of Electronically-Coupled Distributed Resource Units

Abstract: This paper presents closed-form steady-state, fundamental-frequency models of power electronic converter systems for coupling distributed resource (DR) units to the utility power grid. Based on the developed models, the paper introduces a two-step power flow analysis approach that accurately and efficiently represents electronically-coupled DR units. A feature of the proposed approach is that it solves for the internal variables of each DR unit in a non-iterative fashion based on the presented closed-form DR models, and thus, enhances efficiency and accuracy of the solution. This papers provides the details for steady-state closed-form formulation of matrix converter and voltage-sourced ac-dc-ac converter for coupling DR units. However, the presented methodology is conceptually applicable to other types of converter systems. An application of the proposed power flow approach to a micro-grid that includes two electronically-coupled DR units is also presented

Hybrid robust predictive optimization method of power system dispatch

Abstract: A method of power system dispatch control solves power system dispatch problems by integrating a larger variety of generation, load and storage assets, including without limitation, combined heat and power (CHP) units, renewable generation with forecasting, controllable loads, electric, thermal and water energy storage The method employs a predictive algorithm to dynamically schedule different assets in order to achieve global optimization and maintain the system normal operation

Comparative Study of the IEEE 34 Node Test Feeder under Practical Simplifications

Abstract: The IEEE 34 node distribution test feeder incorporates all possible practical configurations and load profiles, such as three phase asymmetry, single phase laterals and distributed loads, among others. Simplifying assumptions leading to the balanced three phase main feeder and spot loads are common in the papers published in the literature on distribution system planning and operation. The purpose of this paper is to compare the results obtained using such simplifications with exact results given in the IEEE node test feeder data. Typical simplifying scenarios are assumed and the resulting balanced system analyzed. Comparison of voltage profiles and system losses validates the use of simplified balanced three phase system in the determination of equipment sizing, location and control parameters.

Applying Time Series to Power Flow Analysis in Networks With High Wind Penetration

Abstract: With high levels of variable renewable generation in distribution or transmission systems, the application of demand and generation time series to power flow analysis can be advantageous. Demand data are often available from historic measurements, while renewable generation such as wind turbine output may be recorded or can be derived from resource measurements over the corresponding period of time. Power flow solutions with hourly time steps over a year or more can then be used to produce load duration curves for system components. This paper shows, by example, how utilities can use the method to determine overload conditions or to specify non-firm connection agreements for new generators.

Electric Power Distribution, Automation, Protection, and Control

Abstract: * Each Chapter Provides an Introduction, Illustrative Examples, and a Summary Introduction to Distribution Automation Systems Historical Background Distribution System Topology and Structure Distribution Automation (DA) and Control Computational Techniques for Distribution Systems Complex Power Concepts Balanced Voltage to Neutral-Connected System Power Relationship for f Y-?-Connected System Per-Unit System Calculation of Power Losses Voltage Regulation Techniques Voltage-Sag Analysis and Calculation Equipment Modeling Components Modeling Distribution System Line Model Distribution Power Flow Analysis Distribution System Topology for Development of Load Flow Review of Classical Power Flow Methods Distribution Power Flow Methods Distribution System Protection and Control Single Line-to-Ground Fault Double Line-to-Ground Fault on Phase B and C Three-Phase Fault Analysis Line-to-Ground and Line-to-Line Faults Protection Systems Protective Relay Technology System Protection in General System Protection for Different Power System Zone Components Distribution System Reliability and Maintenance Reliability Evaluation Terminology/Definitions Reliability Indices Methods of Reliability Analysis Failure Modes and Effects Analysis (FMEA) Method Event-Tree Analysis Method Fault-Tree Analysis Method Unavailability of Power Calculations from the Cut Set Simulation Techniques for Reliability Analysis Simulation Methods Utilized for Distribution Reliability Analysis Evaluation of Distribution Reliability Analysis Method Reliability Database Design Maintenance and Reliability Maintenance of Distribution Systems Reliability-Centered Maintenance Security and Reliability-Centered Maintenance Implementation Plan for Various Component-Maintenance Techniques Distribution Automation and Control Functions Demand-Side Management Voltage/VAr Control Fault Detection (Distribution Automation Function) Trouble Calls Restoration Functions Reconfiguration of Distribution Systems Power Quality Optimization Techniques Intelligent Systems in Distribution Automation Distribution Automation Function Artificial Intelligence Methods Intelligent Systems in Distribution Automation Voltage/VAr Control Network Reconfiguration via AI Fault Detection, Classification, and Location in Distribution Systems Renewable Energy Options and Technology Distributed Generation Working Definition and Classification of Renewable Energy Renewable Energy Options Other Nonrenewable Energy Sources Fuel Cell Distributed Generation Concepts and Benefits Distribution Management Systems Functions of EMS SCADA (Supervisory Control and Data Acquisition) RTU (Remote Terminal Units) Distribution Management System (DMS) Automatic Meter Reading (AMR Cost-Benefit Analysis (CBA) in Distribution Systems Communication Systems for Distribution Automation Systems Telecommunication in Principle Data Communication in Power System Distribution Network Signal Representation Types of Telecommunication Media Communication Modulation Techniques Communication Networking Frame-Relay Communications Communication Standards Overview OSI Model Distribution Network Protocol (DNP) Utility Communication Architecture (UCA) Power-Line Carrier Communication Security in Telecommunications and Information Technology Epilogue Challenges to Distribution Systems for a Competitive Power Utility Environment Protection Demand Response Communication Advances Microgrid Standards and Institutional Barriers Pricing and Billing Glossary References Index

Control of combined storage and generation in distributed energy resources

Abstract: A microsource is provided, which includes an energy storage device, a power generation device, and a controller. The energy storage device is operably coupled for power transfer to a load through a first power bus. The power generation device is operably coupled for power transfer to the load through a second power bus. The controller determines a mode of operation for the energy storage device and the power generation device based on an energy level of the energy storage device and on the load; determines minimum power set points and maximum power set points for the energy storage device and the power generation device based on the determined mode of operation, on a storage output power measured at the first power bus, and on a generation output power measured at the second power bus; and controls an output power of the energy storage device and an output power of the power generation device based on the determined minimum and maximum power set points.

Enhancement of Power System Security through Optimal Placement of TCSC and UPFC

Abstract: In emerging electric power systems, increased transactions often lead to situations where system no longer remains in the secure operating region. The flexible AC transmission system (FACTS) controllers can play an important role in the power system security enhancement. However, due to high capital investment, it is necessary to locate these controllers optimally in the power system. In this paper, a sensitivity based approach has been proposed to decide optimal location of thyristor controlled series compensator (TCSC) and unified power flow controller (UPFC). These factors have been derived in terms of change in a real power flow performance index with respect to their control parameters. The effectiveness of the proposed controllers has been tested on IEEE 30 bus and a 246 bus practical Indian system.

A Kalman Filtering Approach to Rapidly Detecting Modal Changes in Power Systems

Abstract: This paper applies Kalman filtering techniques to the problem of detecting modal changes in large interconnected power systems Short term alarming procedures are developed based on the statistics of the power spectral density of the Kalman filter innovation The new technique is tested on both simulated data and real data obtained from power systems in normal operation The particular advantage of the new method is its ability to detect changes very quickly

Method and system for real-time prediction of power usage for a change to another performance state

Abstract: A method and system for real-time prediction of power usage for a change to another performance state provides input data for power management decision-making processes or for display to system operators. The unit(s) for which power usage is predicted may be a single processor in a uni-processor system or may extend up to the level of facilities within a complex of processing facilities. The method and system gather real-time data on the power consumption of the unit(s) and create a model, such as a regression model, of power versus performance. A resulting power usage change required by a prospective nominal performance state change is shown as display data, or is transmitted to a power budgeting controller to inform the controller as to potential changes that can enhance system operation, such as managing tradeoffs of power allocated to various sub-units of a processing system.

Synthesis and Integration of Future Electronic Power Distribution Systems

Abstract: Future advanced electric power systems will have practically all loads interfaced to energy sources through power electronics equipment. Furthermore, all alternative, sustainable, and distributed energy sources, as well as energy storage systems, can be only connected to electric grid through power electronics converters. This will require new concepts for electronic control of all power flows in order to improve energy availability, power density, and overall energy and power efficiency in all electrical systems, from portable devices to cars, airplanes, ships, homes, data centers, and the power grid. Starting from the example of a computer power system, the paper contemplates possible future ac and dc electronic power system architectures, which fully decouple the dynamics between sources, distribution system, and loads by using separate source-, load-, and distribution-converters. Several ideas and possible methodologies for modeling, analysis, and system-level design of such systems, including power flow control, protection, stability, and subsystem interactions, are presented.

Forecasting Electric Power Generation of Photovoltaic Power System for Energy Network

Abstract: Mitsuru Kudo Member (NTT Energy and Environment System Laboratories, kudo.mitsuru@lab.ntt.co.jp) Akira Takeuchi Member (NTT Energy and Environment System Laboratories, takeuchi.akira@lab.ntt.co.jp) Yousuke Nozaki Member (NTT Energy and Environment System Laboratories, nozaki.yousuke@lab.ntt.co.jp) Hisahito Endo Member (NTT Energy and Environment System Laboratories, endo.hisahito@lab.ntt.co.jp) Jiro Sumita Member (NTT FACILITES,INC., sumita22@ntt-f.co.jp)

Optimal Location and Parameter Setting of TCSC by Both Genetic Algorithm and Particle Swarm Optimization

Abstract: Flexible alternating current transmission systems (FACTS) devices are multi-functional control devices which can be used to effectively control the load flow distribution and the power transfer capability, to reduce active power losses, to improve stabilities of the power network, to decrease the cost of power production and to fulfill the other control requirements by controlling the power flow in the network. However to what extent the performance of FACTS devices can be brought out highly depends upon the location and the parameters of the FACTS devices. In this paper, two techniques, a genetic algorithm (GA) technique and a particle swarm optimization (PSO) technique are used to solve this problem. The present research of the paper aims to select the optimal location and the optimal parameter settings of thyristor controlled series capacitor (TCSC) so as to minimize the active power losses in the power network. To show the validity of the proposed techniques, simulations are carried out on several power systems, a three-bus power system, a five-bus power system, and an IEEE-14 bus power system. All the simulations show very encouraging results. The results are presented in the paper together with appropriate discussion.

Determination of Power System Voltage Stability Using Modal Analysis

Abstract: Voltage instability within the power system has severe consequences including a wide-spread low voltage profile and system blackout. The development and use of accurate methods to predict incipient voltage instability is crucial in preventing such voltage collapse situations. A comparison of the common steady-state methods for voltage stability analysis was undertaken, along with a brief examination into the dynamic approach. Special attention is given to the modal analysis technique presented in [2], which provides both a relative proximity of the system to instability, as well identifies the key contributing factors to instability. A PC-based MATLAB prototype application was developed to assist power system operators in the assessment and analysis of the voltage stability of a power network, at any given operating point, using the modal analysis technique, in addition to useful features such as power flow analysis and traditional V-P/V-Q analysis. Using multiple practical test cases on the IEEE 30 bus system the modal analysis technique was shown to provide an accurate estimate of the system proximity to the voltage stability limit, and to consistently and correctly predict the critical buses and the weakest branches in the transmission system. These results clearly demonstrate the suitability of modal analysis technique as applied to voltage stability analysis, and the need for closer analysis, possible refinement to the method and incorporation into more commercial analysis packages.

Electric power generation system with current-controlled power boost

Abstract: An electric power system includes a variable speed generator driven by an engine and an electrical energy storage device. The generator and the storage device are coupled to a variable voltage DC bus. An inverter converts DC electricity from the DC bus to AC electricity for one or more electrical loads. A detector is included to monitor electric current provided to the DC bus by the storage device and provide a corresponding signal. Control circuitry is responsive to this signal to regulate power output from the storage device to the DC bus.

Gradient non-linear adaptive power architecture and scheme

Abstract: Techniques related to a power module employing multiple power sub-modules are described. More specifically, an embodiment combines and controls multiple power sub- modules of varying characteristics to improve the overall efficiency of the power module across varying load currents, power outputs, input voltages, and other operating conditions. Moreover, the power module may employ an adaptive non-linear and non-uniform current /power sharing among its power sub-modules. Other embodiments are described and claimed.

Tracking maximum loadability conditions in power systems

Abstract: This paper deals with the problem of identifying emergency conditions during system operation in the case of voltage instability. A novel detection scheme is proposed based on measurement of the controlled voltage of bulk power delivery transformers equipped with load tap changers. The detection is based on the comparison of successive post-tap-change voltages. The detection scheme is purely local, even though it senses a system-wide emergency condition. It is shown that the condition detected is a precursor to maximum loadability and voltage instability.

An Optimal Reactive Power Dispatch Model for Deregulated Electricity Markets

Abstract: This paper proposes a reactive power dispatch model that takes into account both the technical and economical aspects associated with reactive power provision in the context of the new operating paradigms in deregulated electricity markets. The main objective of the proposed model is to minimize the total amount of dollars paid by the system operator to the generators for providing the required reactive power support. The real power generation is decoupled and assumed fixed during the reactive power dispatch procedures; however, due to the effect of reactive power on real power, real power generation is allowed be re-scheduled within given limits. The 32-bus CIGRE benchmark system is used to illustrate the proposed reactive power dispatch technique. The developed model is generic in nature and can be adopted for any electricity market structure.

Method and system to influence the power generation of an adjustable speed generator

Abstract: A method and a system to influence the power generation of at least one adjustable speed generator (9) are presented. The system comprises a first voltage source converter (4) connected to a local AC bus (2), where the local AC bus (2) is provided with power by the at least one adjustable speed generator (9), a second voltage source converter (6) connected to an AC grid (8), a DC link (5) connected between the first (4) and the second (6) voltage source converter, and at least one control unit (18) to control the first (4) and the second (6) voltage source converters. The at least one control unit (18) performs the method to control the AC voltage (Vloc) in the local AC bus (2) via the first voltage source converter (4) and to modify a reference value for the AC voltage magnitude (Vloc,ref) of the local AC bus (2) in dependence on the AC voltage magnitude (Vgrid) of the AC grid (8).

Optimal Power Flow to Manage Voltage Profiles in Interconnected Networks Using Expert Systems

Abstract: The optimal power flow issue is one of the most important problems faced by dispatching engineers regarding large scale power systems. It is a particular mathematical approach of the global power system optimization problem that aims at determining the least control movements to keep power system at the most desired state. Thus, it represents a flexible and powerful tool, which can address a wide range of planning and operation studies. However, the complexity of optimal power flow increases dramatically with large-scale networks, which often discourages the utilization of this powerful tool in many applications. This paper proposes a new intelligent approach to facilitate the implementation of the optimal power flow calculations to be utilized in various control centres. A main advantage of the proposed intelligent systems with real control centres is the possibility of controlling the system voltage profile in a tracking mode. The simulation results using this intelligent system when applied to the IEEE 30-bus power network emphasize the validity and effectiveness of the proposed technique.

Redundant power system having a photovoltaic array

Abstract: Systems and methods provide a redundant electrical power supply solution, where an AC power source is called upon when a photovoltaic subsystem is unavailable to meet the power consumption needs of telecommunications site equipment. In one aspect, a system for supplying electrical power includes a DC bus with which telecommunications site equipment is coupled, as well as a photovoltaic subsystem and a second power delivery circuit. The photovoltaic subsystem includes a solar photovoltaic array, a disconnect for controlling electrical connection between the solar photovoltaic array and the DC bus, as well as a DC/DC voltage converter. The second power delivery circuit includes a rectifier for converting incoming AC voltage from an AC power source to output DC voltage delivered at the DC bus upon sensing a condition where the photovoltaic subsystem delivers insufficient DC voltage to the DC bus.

Modeling of STATCOM and UPFC for power system steady state operation and control

Abstract: In recent years, energy, environment, deregulation of power utilities have delayed the construction of both generation facilities and new transmission lines. These problems have necessitated a change in traditional concepts and practices of power systems. There are emerging technologies available, which can help electric companies to deal with above problems. One of such technologies is flexible AC transmission systems (FACTS). Among the converter based FACTS devices static synchronous compensator (STATCOM) and unified power flow controller (UPFC) are the popular FACTS devices. Considering the practical application of the STATCOM and UPFC in power systems, it is of importance and interest to investigate the benefits as well as model these devices for power system steady state operation. We have performed the power flow study of a five bus study system without any FACTS devices and further analyzed it with the converter based FACTS controllers. Programming of the power flow studies stated above is implemented with MATLAB.

Shore power transfer switch

Abstract: A vehicle includes a mobile electric power generation system including a mobile power source such as a generator. An external power interface is included to connect to an external electrical power source. An AC electric power distribution bus is included to power electric loads of the vehicle and a power switch device is provided to selectively provide AC electric power on the power distribution bus from one of the respective power sources with a default to select one of the sources whenever it is present.

Dynamic Power Flow Controllers for transmission corridors

Abstract: The paper presents an approach to evaluate the benefits of a fast controllable power flow control device The device, called dynamic power flow controller (DPFC), is introduced together with its control scheme A generic corridor situation is analyzed for defining the conditions of a beneficial usage of a fast instead of a slow power flow controller The integration of such a fast controller into a market simulation is described A network situation from the UCTE system is chosen to calculate the economic benefits